RTKLIB is adapted for the use of the calibrated TEC during the single-frequency PPP. Among the PPP configurations, it is used the kinematic mode, a combined solution obtained by forward and backward filters, a cut-off angle of 10°, Earth tides corrections, the estimation of tropospheric delay during PPP, IGS precise ephemerides, satellite clock corrections with a 30 s rate (clk\_30s), global positioning system constellation, correction of the phase center variation of the antenna, phase wind up corrections, no strategy for ambiguity solution and corrections of the differential instrumental bias between the civil and precise codes (C1-P1) when P1 was not available. In general, three modes of PPP are analyzed: (1) using the ion-free observation (PPP/if); (2) using L1 and the ionospheric delay from GIMs from UQRG (UPC Quarter an hour Rapid GIM), identified as PPP/uqrg; and (3) using L1 and the calibrated TEC through the proposed method (PPP/tec). Indeed, the PPP/if solutions are obtained using the ion-free observation of the carrier phase, which means that a linear combination is carried out with the L1 and L2 frequencies to eliminate the first-order effect in the ionospheric delay. In the case of PPP/uqrg, the observation used in the PPP Kalman Filter is related to the L1

more easily seen when looking to the single-frequency PPP performance.

GPS satellite.

where the TEC is derived for each GNSS observation, that is, TEC is estimated with the same time resolution as the phase and code collection rate.

Two close GNSS stations located at Rio de Janeiro in Brazil have been selected to make the experiments. The TEC estimation procedure was performed in the station RIOD (lat. Mag. 36.47° S), and the ionospheric delay correction was applied in the station ONRJ, which is located 12 km away. Using the configuration of short distances apart, it is possible to mitigate the problems of spatial gradients of the ionosphere. In addition, the receivers and antennas are from different brands in order to avoid possible correlations between clock and ambiguities of the stations. In this way, it has been as much as possible to isolate the degradation of the ionospheric scintillations in the PPP results.

Prol et al. [95] evaluated the analysis of the performance of the new TEC calibration procedure when applied to PPP for 120 days with six distinct configurations of base and rover stations, and the TEC performance is assessed by applying the estimated TEC from the base station to correct the ionospheric delay in a nearby rover receiver. Just to show the potentiality of the new procedure, here are shown the results of the analysis for two specific days with and without ionospheric scintillations.

**Figure 2** shows an example of the calibrated TEC in RIOD during epochs with and without evidences of ionospheric scintillations. Each colored line represents the slant TEC calculated for a distinct satellite, that is, one colored line refers to the slant TEC of one GPS satellite. The Day Of Year (DOY) 005 of 2013 is shown in the top panel, which refers to the summer solstice in the south crest of EIA. On the other hand, DOY 191 of 2013 is referred to the winter. As it can be seen, the maximum of TEC in the summer solstice reaches around 150 TECU in the slant direction during the daytime. The magnitude of the TEC in daytime is reduced in the winter for up to 100 TECU, mainly due to the reduced intensity of the solar irradiation. However, TEC variability in the daytime is similar. In contrast, the nighttime between 22 and 04 LT presents a significant difference in terms of the TEC variability. The maximum TEC in the nighttime is reduced from 60 TECU in the solstice up to 30 TECU in the winter. Additionally, the high TEC variability evidenced between 22 and 04 LT is associated to the plasma depletions propagating trough the Brazilian region. In fact, the high magnitude of the TEC observations in comparison with the TEC variability makes the impact of the ionospheric GPS Scintillations and Total Electron Content Climatology in the Southern American Sector http://dx.doi.org/10.5772/intechopen.79218 59

being *TE Cij*

58 Accuracy of GNSS Methods

(RMS) maps. In addition, the satellite DCB *Δ b*

of the GNSS signal with the following equation:

time resolution as the phase and code collection rate.

the ionospheric scintillations in the PPP results.

without ionospheric scintillations.

DCB is related to the DCB referential frame defined by IGS.

*gim* the standard deviation of the initial TEC, which is derived from the Global

is obtained from GIMs. Therefore, as the satel-

Ionospheric Maps (GIMs) of the International GNSS Service (IGS) and their root-mean-square

lite DCB and the initial TEC are obtained from GIMs, it is expected that the estimated receiver

Once the ambiguity leveling (first step) and the receiver DCB estimation (second step) are done, the third step consists in the TEC estimation. TEC is directly calculated along the path

*TEC* = *F*[(*λ*1 *φ*1 − 2 *φ*2) − Δ*N* − *c*(Δ *bs* + Δ *br*)], (10)

where the TEC is derived for each GNSS observation, that is, TEC is estimated with the same

Two close GNSS stations located at Rio de Janeiro in Brazil have been selected to make the experiments. The TEC estimation procedure was performed in the station RIOD (lat. Mag. 36.47° S), and the ionospheric delay correction was applied in the station ONRJ, which is located 12 km away. Using the configuration of short distances apart, it is possible to mitigate the problems of spatial gradients of the ionosphere. In addition, the receivers and antennas are from different brands in order to avoid possible correlations between clock and ambiguities of the stations. In this way, it has been as much as possible to isolate the degradation of

Prol et al. [95] evaluated the analysis of the performance of the new TEC calibration procedure when applied to PPP for 120 days with six distinct configurations of base and rover stations, and the TEC performance is assessed by applying the estimated TEC from the base station to correct the ionospheric delay in a nearby rover receiver. Just to show the potentiality of the new procedure, here are shown the results of the analysis for two specific days with and

**Figure 2** shows an example of the calibrated TEC in RIOD during epochs with and without evidences of ionospheric scintillations. Each colored line represents the slant TEC calculated for a distinct satellite, that is, one colored line refers to the slant TEC of one GPS satellite. The Day Of Year (DOY) 005 of 2013 is shown in the top panel, which refers to the summer solstice in the south crest of EIA. On the other hand, DOY 191 of 2013 is referred to the winter. As it can be seen, the maximum of TEC in the summer solstice reaches around 150 TECU in the slant direction during the daytime. The magnitude of the TEC in daytime is reduced in the winter for up to 100 TECU, mainly due to the reduced intensity of the solar irradiation. However, TEC variability in the daytime is similar. In contrast, the nighttime between 22 and 04 LT presents a significant difference in terms of the TEC variability. The maximum TEC in the nighttime is reduced from 60 TECU in the solstice up to 30 TECU in the winter. Additionally, the high TEC variability evidenced between 22 and 04 LT is associated to the plasma depletions propagating trough the Brazilian region. In fact, the high magnitude of the TEC observations in comparison with the TEC variability makes the impact of the ionospheric

*si*

**Figure 2.** TEC estimation with the proposed procedure at RIOD station on 2013 for DOY 005 during the summer (top panel) and DOY 191 during the winter (bottom panel). Each colored line represents the slant TEC calculated for a distinct GPS satellite.

scintillation not so clearing TEC. However, the impact of the ionospheric scintillations is much more easily seen when looking to the single-frequency PPP performance.

RTKLIB is adapted for the use of the calibrated TEC during the single-frequency PPP. Among the PPP configurations, it is used the kinematic mode, a combined solution obtained by forward and backward filters, a cut-off angle of 10°, Earth tides corrections, the estimation of tropospheric delay during PPP, IGS precise ephemerides, satellite clock corrections with a 30 s rate (clk\_30s), global positioning system constellation, correction of the phase center variation of the antenna, phase wind up corrections, no strategy for ambiguity solution and corrections of the differential instrumental bias between the civil and precise codes (C1-P1) when P1 was not available. In general, three modes of PPP are analyzed: (1) using the ion-free observation (PPP/if); (2) using L1 and the ionospheric delay from GIMs from UQRG (UPC Quarter an hour Rapid GIM), identified as PPP/uqrg; and (3) using L1 and the calibrated TEC through the proposed method (PPP/tec). Indeed, the PPP/if solutions are obtained using the ion-free observation of the carrier phase, which means that a linear combination is carried out with the L1 and L2 frequencies to eliminate the first-order effect in the ionospheric delay. In the case of PPP/uqrg, the observation used in the PPP Kalman Filter is related to the L1 frequency but corrected from the ionospheric delay derived from UQRG GIMs. The PPP/tec is similar to PPP/uqrg, but the ionospheric delay is derived directly from Eq. (10). The reference coordinates of ONRJ has been obtained from the Sistema de Referencia Geocéntrico para las Américas (SIRGAS) final solutions at epoch 2013, where a time update was performed to make the coordinates consistent with the PPP solutions.

was 0.19 m with a standard deviation of 0.05 m and the RMSE of PPP/uqrg was 0.70 m with a standard deviation of 0.66 m. By itself, this is an outstanding result, since many researchers have already used single-frequency receivers and ionospheric corrections to obtain, in general, an absolute accuracy of 0.5 m in the horizontal and 1 m in vertical for the kinematic PPP [96–98]. Now, we are showing the possibility of obtaining the single-frequency PPP accuracy similar to that from dual-frequency PPP. The horizontal accuracy in the experiment for PPP/tec was 0.12 m in DOY 005 and 0.05 m in DOY 191 and the vertical accuracy was 0.15 m in DOY 005 and 0.07 m in DOY 191. These accuracies are compatible to the double-frequency solutions. Therefore, the unique consideration for a high accuracy in single-frequency PPP is that TEC needs to be sufficient precise, which was not realistic in some epochs of DOY 005 due to the ionospheric scintillations.

GPS Scintillations and Total Electron Content Climatology in the Southern American Sector

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61

A noticeable degradation of the PPP solution occurs between 00 and 04 hours LT in the summer solstice due to the high TEC variability. This PPP degradation is related to the ionospheric irregularities that impact GPS observations more effectively. At such instances, the uplifted ionosphere due to the pre-reversal drift produces high vertical gradients. It is believed that these gradients set the preconditions for plasma instability, controlling the generation of ionospheric irregularities. Therefore, the change of the GPS signal phase and amplitude imposed by ionospheric irregularities degrades the PPP solution. It is interesting to note that the PPP/if is sensitive, but not too much, to the ionospheric scintillations. In case of PPP/uqrg, it is hard to see the impact because of the high standard deviation in the PPP solution at other epochs. However, the impact of the scintillations is very evident in PPP/tec. This mainly happens because the estimated TEC was set to be very precise during the PPP, so that TEC was included with small values for standard deviation in the PPP Kalman filter. At epochs where only the first-order ionospheric delay is supposed to affect the GPS observations, the PPP/tec solution is very accurate. At epochs where the high-orders terms of the ionosphere delay impact the GPS signal, the

The ionospheric conditions are affected by electrodynamic processes that are driven by solar phenomena. During quiet geomagnetic periods, the effects are clearly associated with the seasonal variation of the solar illumination and with the 11-year solar radiation variation. These conditions can be strongly disturbed under the impact of CMEs (coronal mass ejections) and HSS (high-speed streams) in the magnetosphere producing the geomagnetic storms, which result in steeper electron density gradients and stronger irregularities. These irregularities are responsible for fluctuations in the amplitude and phase of GNSS signals, which can degrade the accuracy of the measurements. Therefore, the climatology of these irregularities is very

The investigation of ionospheric scintillations over South America has shown that they can occur at all longitudinal sectors during quiet geomagnetic periods, but they are stronger at post-sunset hours in the crest regions of the EIA (equatorial ionospheric anomaly), and seems to be more intense in the southern EIA crest, which is under the effect of the SAMA (South American Magnetic Anomaly) [24, 37, 81]. The scintillation occurrences strongly enhance with the increase of the solar activity [20, 21, 35, 37, 99], and during geomagnetic disturbed

important to define its spatial distribution and time of occurrence.

PPP degradation becomes evident.

**5. Conclusions**

periods [13, 38, 75, 93, 94].

**Figure 3** shows the performance of PPP/if, PPP/tec and PPP/uqrg in terms of the threedimensional (3D) error of the estimated coordinates. Each point represents the error of the PPP solution calculated in each processing epoch in kinematic mode. Since it was used a combined filter of forward and backward solution, there is no need for time convergence in the solution. Consequently, the remaining errors are related to the terms not efficiently mitigated and, as can be seen, the PPP/tec (blue points) was obtained with a high accuracy in many hours, except to the hours when is typically observed ionospheric scintillations.

In general, the proposed method allowed having the single-frequency PPP with a similar accuracy than the double-frequency PPP. The root mean square error (RMSE) obtained for PPP/if in DOY 191 was 0.04 m with a standard of 0.04 m, the RMSE of PPP/tec was 0.09 m with a standard deviation of 0.04 m and the RMSE of PPP/uqrg was 0.47 m with a standard deviation of 0.65 m. In the case of DOY 005, the RMSE of PPP/if was 0.04 m with a standard of 0.04 m, the RMSE of PPP/tec

**Figure 3.** 3D error of PPP at ONRJ station on 2013 for DOY 005 during summer (top panel) and DOY 191 during winter (bottom panel).

was 0.19 m with a standard deviation of 0.05 m and the RMSE of PPP/uqrg was 0.70 m with a standard deviation of 0.66 m. By itself, this is an outstanding result, since many researchers have already used single-frequency receivers and ionospheric corrections to obtain, in general, an absolute accuracy of 0.5 m in the horizontal and 1 m in vertical for the kinematic PPP [96–98]. Now, we are showing the possibility of obtaining the single-frequency PPP accuracy similar to that from dual-frequency PPP. The horizontal accuracy in the experiment for PPP/tec was 0.12 m in DOY 005 and 0.05 m in DOY 191 and the vertical accuracy was 0.15 m in DOY 005 and 0.07 m in DOY 191. These accuracies are compatible to the double-frequency solutions. Therefore, the unique consideration for a high accuracy in single-frequency PPP is that TEC needs to be sufficient precise, which was not realistic in some epochs of DOY 005 due to the ionospheric scintillations.

A noticeable degradation of the PPP solution occurs between 00 and 04 hours LT in the summer solstice due to the high TEC variability. This PPP degradation is related to the ionospheric irregularities that impact GPS observations more effectively. At such instances, the uplifted ionosphere due to the pre-reversal drift produces high vertical gradients. It is believed that these gradients set the preconditions for plasma instability, controlling the generation of ionospheric irregularities. Therefore, the change of the GPS signal phase and amplitude imposed by ionospheric irregularities degrades the PPP solution. It is interesting to note that the PPP/if is sensitive, but not too much, to the ionospheric scintillations. In case of PPP/uqrg, it is hard to see the impact because of the high standard deviation in the PPP solution at other epochs. However, the impact of the scintillations is very evident in PPP/tec. This mainly happens because the estimated TEC was set to be very precise during the PPP, so that TEC was included with small values for standard deviation in the PPP Kalman filter. At epochs where only the first-order ionospheric delay is supposed to affect the GPS observations, the PPP/tec solution is very accurate. At epochs where the high-orders terms of the ionosphere delay impact the GPS signal, the PPP degradation becomes evident.

#### **5. Conclusions**

frequency but corrected from the ionospheric delay derived from UQRG GIMs. The PPP/tec is similar to PPP/uqrg, but the ionospheric delay is derived directly from Eq. (10). The reference coordinates of ONRJ has been obtained from the Sistema de Referencia Geocéntrico para las Américas (SIRGAS) final solutions at epoch 2013, where a time update was performed to

**Figure 3** shows the performance of PPP/if, PPP/tec and PPP/uqrg in terms of the threedimensional (3D) error of the estimated coordinates. Each point represents the error of the PPP solution calculated in each processing epoch in kinematic mode. Since it was used a combined filter of forward and backward solution, there is no need for time convergence in the solution. Consequently, the remaining errors are related to the terms not efficiently mitigated and, as can be seen, the PPP/tec (blue points) was obtained with a high accuracy in many hours, except to the hours when is typically observed ionospheric scintillations.

In general, the proposed method allowed having the single-frequency PPP with a similar accuracy than the double-frequency PPP. The root mean square error (RMSE) obtained for PPP/if in DOY 191 was 0.04 m with a standard of 0.04 m, the RMSE of PPP/tec was 0.09 m with a standard deviation of 0.04 m and the RMSE of PPP/uqrg was 0.47 m with a standard deviation of 0.65 m. In the case of DOY 005, the RMSE of PPP/if was 0.04 m with a standard of 0.04 m, the RMSE of PPP/tec

**Figure 3.** 3D error of PPP at ONRJ station on 2013 for DOY 005 during summer (top panel) and DOY 191 during winter

(bottom panel).

make the coordinates consistent with the PPP solutions.

60 Accuracy of GNSS Methods

The ionospheric conditions are affected by electrodynamic processes that are driven by solar phenomena. During quiet geomagnetic periods, the effects are clearly associated with the seasonal variation of the solar illumination and with the 11-year solar radiation variation. These conditions can be strongly disturbed under the impact of CMEs (coronal mass ejections) and HSS (high-speed streams) in the magnetosphere producing the geomagnetic storms, which result in steeper electron density gradients and stronger irregularities. These irregularities are responsible for fluctuations in the amplitude and phase of GNSS signals, which can degrade the accuracy of the measurements. Therefore, the climatology of these irregularities is very important to define its spatial distribution and time of occurrence.

The investigation of ionospheric scintillations over South America has shown that they can occur at all longitudinal sectors during quiet geomagnetic periods, but they are stronger at post-sunset hours in the crest regions of the EIA (equatorial ionospheric anomaly), and seems to be more intense in the southern EIA crest, which is under the effect of the SAMA (South American Magnetic Anomaly) [24, 37, 81]. The scintillation occurrences strongly enhance with the increase of the solar activity [20, 21, 35, 37, 99], and during geomagnetic disturbed periods [13, 38, 75, 93, 94].

It was presented the potentiality of a new procedure for TEC calibration, showing a useful tool to correct the first-order ionospheric delay that improves the traditional single-frequency PPP solutions. Additionally, the results show a high-sensitive solution of PPP/tec to the ionospheric scintillations, even more sensitive in comparison with the impact of the ionospheric scintillation in the TEC level, which indicates that this kind of procedures are emerging as having potential for a wide range of applications for those measuring and predicting the ionospheric scintillations.

[2] Prolss GW. Ionospheric storms at mid-latitude: A short review. In: Kintner PM Jr, Coster AJ, Fuller-Rowell T, Mannucci AJ, Mendillo M, Heelis R, editors. Midlatitude Ionospheric Dynamics and Disturbances, Geophysical Monograph Series. Vol. 181. Washington, D.C:

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63

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[6] Yizengaw E, Dyson PL, Essex EA, Moldwin MB. Ionosphere dynamics over the southern hemisphere during the 31 march 2001 severe magnetic storm using multi instrument measurement data. Annales Geophysicae. 2005;**23**:707-721. DOI: 10.5194/angeo-23-707-2005 [7] Mendillo M. Storms in the ionosphere: Patterns and processes for total electron content.

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[11] Horvath I, Lovell BC. Storm-enhanced plasma density and polar tongue of ionization development during the 15 May 2005 super storm. Journal of Geophysical Research-

[12] Prikryl P, Ghoddousi-Fard R, Weygand JM, Viljanen A, Connors M, Danskin DW, Jayachandran PT, Jacobsen KS, Andalsvik YL, Thomas EG, Ruohoniemi JM, Durgonics T, Oksavik K, Zhang Y, Spanswick E, Aquino M, Sreeja V. GPS phase scintillation at high latitudes during the geomagnetic storm of 17-18 March 2015. Journal of Geophysical

[13] Correia E, Spogli L, Alfonsi L, Cesaroni C, Gulisano AM, Thomas EG, Ramirez RFH, Rodel AA. Ionospheric F-region response to the 26 September 2011 geomagnetic storm in the Antarctica American and Australian sectors. Annales Geophysicae. 2017;**35**:1113-

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Space. 2013;**118**:1180-1189. DOI: 10.1002/jgra.50116

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1129. DOI: 10.5194/angeo-35-1113-2017

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AGU; 2008. pp. 9-24. DOI: 10.1029/181GM03

DOI: 10.1023/A:1005107532631

DOI: 10.1029/2003JA010342

#### **Acknowledgements**

EC thanks the National Council for Research and Development (CNPq) for individual research support (processes nos. 556872/2009-6, 406690/2013-8, 303299/2016-9) and the National Institute for Space Research (INPE/MCTI). MTAHM thanks the support from CNPq through grant no. 429885/2016-4. FSP and POC are grateful to CNPq (grant no. 309924/2013-8), Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP grant no. 2015/15027-7) and to Faculdade de Ciências e Tecnologia of UNESP (FCT/UNESP).

#### **Conflict of interest**

The authors declare that they have no conflict of interest.

#### **Author details**

Emília Correia1,2\*, Marcio Tadeu de Assis Honorato Muella3 , Lucilla Alfonsi4 , Fabricio dos Santos Prol5 and Paulo de Oliveira Camargo5

#### **References**

[1] Prolss GW.Ionospheric F-region storms. In: Volland H, editor. Handbook of Atmospheric Electrodynamics. Florida: CRC Press; 1995. pp. 195-248

[2] Prolss GW. Ionospheric storms at mid-latitude: A short review. In: Kintner PM Jr, Coster AJ, Fuller-Rowell T, Mannucci AJ, Mendillo M, Heelis R, editors. Midlatitude Ionospheric Dynamics and Disturbances, Geophysical Monograph Series. Vol. 181. Washington, D.C: AGU; 2008. pp. 9-24. DOI: 10.1029/181GM03

It was presented the potentiality of a new procedure for TEC calibration, showing a useful tool to correct the first-order ionospheric delay that improves the traditional single-frequency PPP solutions. Additionally, the results show a high-sensitive solution of PPP/tec to the ionospheric scintillations, even more sensitive in comparison with the impact of the ionospheric scintillation in the TEC level, which indicates that this kind of procedures are emerging as having potential for a wide range of applications for those measuring and predicting the

EC thanks the National Council for Research and Development (CNPq) for individual research support (processes nos. 556872/2009-6, 406690/2013-8, 303299/2016-9) and the National Institute for Space Research (INPE/MCTI). MTAHM thanks the support from CNPq through grant no. 429885/2016-4. FSP and POC are grateful to CNPq (grant no. 309924/2013-8), Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP grant no. 2015/15027-7)

, Lucilla Alfonsi4

,

and to Faculdade de Ciências e Tecnologia of UNESP (FCT/UNESP).

The authors declare that they have no conflict of interest.

Emília Correia1,2\*, Marcio Tadeu de Assis Honorato Muella3

\*Address all correspondence to<EMAIL_ADDRESS>
2 CRAAM-Presbiterian Mackenzie University, São Paulo, Brazil

and Paulo de Oliveira Camargo5

[1] Prolss GW.Ionospheric F-region storms. In: Volland H, editor. Handbook of Atmospheric

1 National Institute for Space Research - INPE, São José dos Campos, Brazil

3 University of Vale do Paraíba - UNIVAP, São José dos Campos, Brazil 4 National Institute of Geophysics and Vulcanology - INGV, Rome, Italy

5 Universidade Estadual Paulista-UNESP, Presidente Prudente, Brazil

Electrodynamics. Florida: CRC Press; 1995. pp. 195-248

ionospheric scintillations.

62 Accuracy of GNSS Methods

**Acknowledgements**

**Conflict of interest**

**Author details**

**References**

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**Chapter 5**

**Provisional chapter**

**Evaluation of GNSS Data with Internet Based Services:**

**Evaluation of GNSS Data with Internet Based Services:**

Nowadays, as the Internet services are developed, it becomes possible to offer services for many applications in the engineering field online via the Internet. One of these services is the evaluation of online GPS data. The most important feature of Internet-based applications is that these services are free and easy to use. In this study, the data of Global Navigation Satellite Systems (GNSS) of different periods belonging to newly established HRUH permanent GNSS station in Harran University were evaluated through Internetbased services. The evaluation strategy of GNSS data was conducted in 1-, 2-, 6-, 12-, and 24-h campaigns, and the results were compared between different Internet site solution results. When the results obtained are examined, it can be said that the accuracy of the data obtained from these services can be used in many applications requiring precision

**Keywords:** PPP, GNSS, RINEX, internet-based GNSS evaluation services, positioning

Recently, web-based GNSS positioning services have begun to be developed as an additional option to classical evaluation methods. Such services produce solutions automatically by using some of the GNSSS observations loaded via the web interface over the Internet. GNSS observations collected in the field are recorded in standard data formats such as Receiver INdependent EXchange (RINEX) and then uploaded to web-based positioning services, allowing location coordinates of observation points to be obtained in short time and free of

in centimeter levels and is capable of satisfying the expectancies.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

DOI: 10.5772/intechopen.79064

**The Case of HRUH Station**

**The Case of HRUH Station**

http://dx.doi.org/10.5772/intechopen.79064

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

Mustafa Ulukavak

Mustafa Ulukavak

**Abstract**

accuracy

**1. Introduction**

charge [1–3].

#### **Evaluation of GNSS Data with Internet Based Services: The Case of HRUH Station Evaluation of GNSS Data with Internet Based Services: The Case of HRUH Station**

DOI: 10.5772/intechopen.79064

#### Mustafa Ulukavak Mustafa Ulukavak

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79064

#### **Abstract**

Nowadays, as the Internet services are developed, it becomes possible to offer services for many applications in the engineering field online via the Internet. One of these services is the evaluation of online GPS data. The most important feature of Internet-based applications is that these services are free and easy to use. In this study, the data of Global Navigation Satellite Systems (GNSS) of different periods belonging to newly established HRUH permanent GNSS station in Harran University were evaluated through Internetbased services. The evaluation strategy of GNSS data was conducted in 1-, 2-, 6-, 12-, and 24-h campaigns, and the results were compared between different Internet site solution results. When the results obtained are examined, it can be said that the accuracy of the data obtained from these services can be used in many applications requiring precision in centimeter levels and is capable of satisfying the expectancies.

**Keywords:** PPP, GNSS, RINEX, internet-based GNSS evaluation services, positioning accuracy

#### **1. Introduction**

Recently, web-based GNSS positioning services have begun to be developed as an additional option to classical evaluation methods. Such services produce solutions automatically by using some of the GNSSS observations loaded via the web interface over the Internet. GNSS observations collected in the field are recorded in standard data formats such as Receiver INdependent EXchange (RINEX) and then uploaded to web-based positioning services, allowing location coordinates of observation points to be obtained in short time and free of charge [1–3].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Web-based positioning services have been considered as an alternative to scientific or commercial software for 15 years. Wherever the Internet access is available, it is easier to evaluate RINEX data using such services. Another reliable aspect of preferring web-based GNSS software is the use of reliable scientific software (Bernese, Gamit, GIPSY/OASIS II, etc.) running in the background of these systems. These services also provide many advantages to the user by reducing the cost of many software, hardware, tools, personnel and transportation services. The results of evaluations of GNSS observations uploaded to these services also provide many advantages such as the possibility of downloading results from the web interface or sending the results to the users via e-mail. The results from these services are in the form of a summary or detailed report. The standard deviation values of these points are sent together with the estimated point coordinates in the incoming reports. Some services send out summary reports in the form of short summary information, while some services provide detailed reports with detailed and graphical presentations. Many of these services are free and some of them require free membership for accessing with a user name and password while using. In general, these services use the data and products of the high accurate and precise International GNSS Service (IGS). IGS provides these products with high precision of GPS/GLONASS ephemeris, satellite and station clocks, earth orientation parameters (ERP), IGS stations coordinates and velocities, and atmospheric parameters to users. These services provided by IGS have led to the emergence of new approaches and new evaluation methods in positioning with the accuracy increase in data processing, orbit determination, and acquisition of clock information in satellite geodesy [4].

1-, 2-, 6-, 12-, and 24-h GNSS observations of the HRUH permanent GNSS station which is established on the roof of the GNSS Laboratory of Harran University Geomatics Engineering Department are evaluated for each web-based positioning service. Then, the same GNSS observations of this station are compared with the analysis results (coordinates and standard deviations) with the scientific GNSS-Inferred Positioning System and Orbit Analysis

Evaluation of GNSS Data with Internet Based Services: The Case of HRUH Station

http://dx.doi.org/10.5772/intechopen.79064

75

The widespread use of satellite and space techniques has become an indispensable tool in satellite positioning. Nowadays, by using developed techniques and methods, highly accurate position information is obtained with the help of positioning algorithms. These techniques often differ according to the data collection method. Absolute and relative positioning methods from the earliest times of use of positioning systems are the most preferred techniques for application purposes. The relative positioning technique requires at least two receivers to be used by simultaneous GNSS observations. However, PPP is a method that can be applied by removing this necessity. The PPP technique is based on the evaluation of the code and phase measurements collected from a single receiver. In this technique, the receiver position is directly determined by using precise orbits and clock corrections issued by IGS and similar organizations [5, 6]. The success of the positioning with the PPP technique depends largely on the determination of precise orbit changes of GPS satellites. Therefore, in PPP solutions, it is important to obtain precise orbit (ultra-rapid, rapid, and final) and satellite clock information instead of orbital information broadcast from satellites. Accuracy, broadcast latency, update and sample interval for accurate GPS satellite orbits and clock corrections published by IGS

Nowadays, as the accuracy of precise satellite orbits and clock products published by organizations such as IGS, CODE, and JPL advances, the use of PPP technique is gradually increas-

The ionosphere-independent observation equations of pseudorange and carrier phase measurements include receiver location, clock offset, tropospheric delay, carrier phase unknown

*r* + *εp*

are the ionosphere-independent combination of the code and phase measure-

is the ionospheric signal delay between the satellite and the receiver; *λ* is

*r* + *εϕ*

(1)

is the tropospheric

*p* = *ρ* + *c*(*dt* − *dT*) + *Tr* + *I*

*N* is the integer ambiguity of the ionosphere-independent carrier phase; *Tr*

 *l ϕ* = *ρ* + *c*(*dt* − *dT*) + *N* + *Tr* + *I*

ments, respectively; *dt* is the receiver clock offset which is the difference between receiver time (receiver clock) and system time (GPS); *dT* is the satellite clock offset which is the difference between satellite time (satellite clock) and system time (GPS); *c* is the speed of light in space;

Simulation Software (GIPSY/OASIS II) developed by NASA's JPL laboratory.

**2. Precise point positioning (PPP)**

are given in **Table 1**.

where *l p* and *l ϕ*

signal delay, and *I*

ing in determining the point positions.

parameters, and observation errors:

*r*

*l*

Web-based positioning services have introduced two different types of solutions. The first is the relative positioning approach and the second is the precise point positioning (PPP) solution approach. In this study, web-based precise point positioning solution will be mentioned. The services that are mainly used for the PPP solution approach use only GPS or GPS + GLONASS products such as orbits and clock corrections. The data flow for both webbased positioning services is shown in **Figure 1**.

In this study, four different web-based PPP services, which are most well known and widely used, general properties of services, accessing addresses and analysis results are examined.

**Figure 1.** Schematic presentation of web-based positioning services.

1-, 2-, 6-, 12-, and 24-h GNSS observations of the HRUH permanent GNSS station which is established on the roof of the GNSS Laboratory of Harran University Geomatics Engineering Department are evaluated for each web-based positioning service. Then, the same GNSS observations of this station are compared with the analysis results (coordinates and standard deviations) with the scientific GNSS-Inferred Positioning System and Orbit Analysis Simulation Software (GIPSY/OASIS II) developed by NASA's JPL laboratory.

#### **2. Precise point positioning (PPP)**

Web-based positioning services have been considered as an alternative to scientific or commercial software for 15 years. Wherever the Internet access is available, it is easier to evaluate RINEX data using such services. Another reliable aspect of preferring web-based GNSS software is the use of reliable scientific software (Bernese, Gamit, GIPSY/OASIS II, etc.) running in the background of these systems. These services also provide many advantages to the user by reducing the cost of many software, hardware, tools, personnel and transportation services. The results of evaluations of GNSS observations uploaded to these services also provide many advantages such as the possibility of downloading results from the web interface or sending the results to the users via e-mail. The results from these services are in the form of a summary or detailed report. The standard deviation values of these points are sent together with the estimated point coordinates in the incoming reports. Some services send out summary reports in the form of short summary information, while some services provide detailed reports with detailed and graphical presentations. Many of these services are free and some of them require free membership for accessing with a user name and password while using. In general, these services use the data and products of the high accurate and precise International GNSS Service (IGS). IGS provides these products with high precision of GPS/GLONASS ephemeris, satellite and station clocks, earth orientation parameters (ERP), IGS stations coordinates and velocities, and atmospheric parameters to users. These services provided by IGS have led to the emergence of new approaches and new evaluation methods in positioning with the accuracy increase in data processing, orbit determination, and acquisition of clock information in satellite geodesy [4]. Web-based positioning services have introduced two different types of solutions. The first is the relative positioning approach and the second is the precise point positioning (PPP) solution approach. In this study, web-based precise point positioning solution will be mentioned. The services that are mainly used for the PPP solution approach use only GPS or GPS + GLONASS products such as orbits and clock corrections. The data flow for both web-

In this study, four different web-based PPP services, which are most well known and widely used, general properties of services, accessing addresses and analysis results are examined.

based positioning services is shown in **Figure 1**.

74 Accuracy of GNSS Methods

**Figure 1.** Schematic presentation of web-based positioning services.

The widespread use of satellite and space techniques has become an indispensable tool in satellite positioning. Nowadays, by using developed techniques and methods, highly accurate position information is obtained with the help of positioning algorithms. These techniques often differ according to the data collection method. Absolute and relative positioning methods from the earliest times of use of positioning systems are the most preferred techniques for application purposes. The relative positioning technique requires at least two receivers to be used by simultaneous GNSS observations. However, PPP is a method that can be applied by removing this necessity. The PPP technique is based on the evaluation of the code and phase measurements collected from a single receiver. In this technique, the receiver position is directly determined by using precise orbits and clock corrections issued by IGS and similar organizations [5, 6]. The success of the positioning with the PPP technique depends largely on the determination of precise orbit changes of GPS satellites. Therefore, in PPP solutions, it is important to obtain precise orbit (ultra-rapid, rapid, and final) and satellite clock information instead of orbital information broadcast from satellites. Accuracy, broadcast latency, update and sample interval for accurate GPS satellite orbits and clock corrections published by IGS are given in **Table 1**.

Nowadays, as the accuracy of precise satellite orbits and clock products published by organizations such as IGS, CODE, and JPL advances, the use of PPP technique is gradually increasing in determining the point positions.

The ionosphere-independent observation equations of pseudorange and carrier phase measurements include receiver location, clock offset, tropospheric delay, carrier phase unknown parameters, and observation errors:

$$\begin{aligned} \text{errors:}\\ l\_p &= \rho + c(dt - dT) + T\_r + I\_r + \varepsilon\_p\\ l\_q &= \rho + c(dt - dT) + N\lambda + T\_r + I\_r + \varepsilon\_q \end{aligned} \tag{1}$$

where *l p* and *l ϕ* are the ionosphere-independent combination of the code and phase measurements, respectively; *dt* is the receiver clock offset which is the difference between receiver time (receiver clock) and system time (GPS); *dT* is the satellite clock offset which is the difference between satellite time (satellite clock) and system time (GPS); *c* is the speed of light in space; *N* is the integer ambiguity of the ionosphere-independent carrier phase; *Tr* is the tropospheric signal delay, and *I r* is the ionospheric signal delay between the satellite and the receiver; *λ* is

**Table 1.** Accurate GPS satellite orbits and clock corrections issued by IGS.

the wavelength; *εp* and *εϕ* are the noise components including the signal reflection [5, 6]. The geometric distance between satellite (*XS* , *YS* , *ZS* ) and receiver (*XR* , *YR* , *ZR* ) is defined as: (*XS* − *XR*)2 + (*YS* − *YR*)2 + (*ZS* − *ZR*)2 (2)

$$\rho = \sqrt{(X^{\mathbb{S}} - \overline{X\_{\mathbb{R}}})^2 + \left(Y^{\mathbb{S}} - \overline{Y\_{\mathbb{R}}}\right)^2 + \left(Z^{\mathbb{S}} - \overline{Z\_{\mathbb{R}}}\right)^2} \tag{2}$$

more training-, information-, and experience-related requirements. In such software, different parameters used in the evaluation can provide a different significance in the results. A third type of software that can process GNSS observations is web-based positioning services. In this service, it is necessary to have only one GNSS receiver and an Internet connection in order to be able to generate the point position information if the observations in the GNSS receiver are aggregated in whatever manner the observations are aggregated in static or kinematic methods. There is no need for any additional financing or equipment other than these equipment. Web-based GNSS services are simple to use and require no additional software knowledge. The data in the RINEX format obtained from the GNSS receivers are processed by uploading them to the web interface of web-based positioning services. Depending on the service to be used, some services require additional information such as the receiving antenna brand and antenna height. At the end of the evaluation process initiated after the uploading process of the GNSS observations, the final report of the relevant GNSS observations is presented to the user via e-mail or a link that can be downloaded from the web interface. The Internet addresses of the web-based positioning services that can process GNSS observations accord-

php?locale=en

https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.

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77

http://gaps.gge.unb.ca/submitadvanced.php

http://apps.gdgps.net/apps\_file\_upload.php

https://magicgnss.gmv.com/user/ppp

All of the services mentioned in **Table 2** have limited use. However, they use scientific and academic software in the background to determine the station coordinates. These services present the resultant product using the commonly accepted parameters of the data processing methods for coordinate production from GNSS observations in the literature. The web-based

Canadian Spatial Reference System Precise Point Positioning (CSRS-PPP) is a web-based GPS observations processing service provided by the Natural Resources Canada (NRCAN). This service works with a membership system that has the ability to process GNSS observations

ing to the PPP method and provide them to the users are given in **Table 2**.

**PPP service name Organizations Web pages (March, 2018)**

Natural Resources Canada (NRC)

University of New Brunswick (UNB)

NASA- Jet Propulsion Laboratory (JPL)

**Table 2.** Online services using PPP solution approach.

GMV Aerospace and Defence S.A.U.

CSRS-PPP: Canadian Spatial Reference System- Precise Point Positioning

GAPS: GPS Analysis and Positioning Software

APPS: Automatic Precise Positioning Service

magicGNSS: magic Precise Point Positioning

Solution

**3.1. CSRS-PPP: Canadian spatial reference system-precise point positioning**

positioning services used in this study are:

PPP technology has different software options such as Bernese, Gamit, GIPSY/OASIS II to determine the position.

#### **3. GNSS measurements processing software**

Today, we can classify software that can evaluate GNSS measurements in three different groups. The first of these is commercial software. Commercial software is a software that is bundled with the GNSS set, which is often used in practical engineering applications and is usually purchased by customer companies. These are the more preferred software by institutions and organizations that best determine the solutions offered by the company in order to avoid any problems from the users. Other software that can process GNSS measurements are scientific software. Scientific software has been fully developed at research centers and universities for use in academic and scientific studies. The use of scientific software is more complex than commercial software and web-based data processing services. For this reason, there are

**Table 2.** Online services using PPP solution approach.

the wavelength; *εp*

76 Accuracy of GNSS Methods

determine the position.

and *εϕ*

Sat. and Stn. clocks

Sat. and Stn. clocks

**Table 1.** Accurate GPS satellite orbits and clock corrections issued by IGS.

**3. GNSS measurements processing software**

geometric distance between satellite (*XS*

*ρ* = √

are the noise components including the signal reflection [5, 6]. The

, *YR* , *ZR*

(*XS* − *XR*)2 + (*YS* − *YR*)2 + (*ZS* − *ZR*)2 (2)

) is defined as:

**interval**

5 min

Sat.: 30s Stn.:5 min

) and receiver (*XR*

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_

PPP technology has different software options such as Bernese, Gamit, GIPSY/OASIS II to

Today, we can classify software that can evaluate GNSS measurements in three different groups. The first of these is commercial software. Commercial software is a software that is bundled with the GNSS set, which is often used in practical engineering applications and is usually purchased by customer companies. These are the more preferred software by institutions and organizations that best determine the solutions offered by the company in order to avoid any problems from the users. Other software that can process GNSS measurements are scientific software. Scientific software has been fully developed at research centers and universities for use in academic and scientific studies. The use of scientific software is more complex than commercial software and web-based data processing services. For this reason, there are

, *YS* , *ZS*

**Type Accuracy Latency Updates Sample**

Broadcast Orbits ~100 cm Real time --- Daily

~2.5 ns SDev Ultra-rapid (predicted) Orbits ~5 cm Real time At 03, 09, 15, 21 UTC 15 min

~1.5 ns SDev Ultra-rapid (observed) Orbits ~3 cm 3–9 h At 03, 09, 15, 21 UTC 15 min

~50 ps SDev Rapid Orbits ~2.5 cm 17–41 h At 17 UTC daily 15 min

> ~75 ps RMS ~25 ps SDev

> ~75 ps RMS ~20 ps SDev

Final Orbits ~2.5 cm 12–18 days Every Thursday 15 min

Sat. clocks ~5 ns RMS

Sat. clocks ~3 ns RMS

Sat. clocks ~150 ps RMS

more training-, information-, and experience-related requirements. In such software, different parameters used in the evaluation can provide a different significance in the results. A third type of software that can process GNSS observations is web-based positioning services. In this service, it is necessary to have only one GNSS receiver and an Internet connection in order to be able to generate the point position information if the observations in the GNSS receiver are aggregated in whatever manner the observations are aggregated in static or kinematic methods. There is no need for any additional financing or equipment other than these equipment. Web-based GNSS services are simple to use and require no additional software knowledge. The data in the RINEX format obtained from the GNSS receivers are processed by uploading them to the web interface of web-based positioning services. Depending on the service to be used, some services require additional information such as the receiving antenna brand and antenna height. At the end of the evaluation process initiated after the uploading process of the GNSS observations, the final report of the relevant GNSS observations is presented to the user via e-mail or a link that can be downloaded from the web interface. The Internet addresses of the web-based positioning services that can process GNSS observations according to the PPP method and provide them to the users are given in **Table 2**.

All of the services mentioned in **Table 2** have limited use. However, they use scientific and academic software in the background to determine the station coordinates. These services present the resultant product using the commonly accepted parameters of the data processing methods for coordinate production from GNSS observations in the literature. The web-based positioning services used in this study are:

#### **3.1. CSRS-PPP: Canadian spatial reference system-precise point positioning**

Canadian Spatial Reference System Precise Point Positioning (CSRS-PPP) is a web-based GPS observations processing service provided by the Natural Resources Canada (NRCAN). This service works with a membership system that has the ability to process GNSS observations from single- or dual-frequency receivers based on static or PPP techniques. CSRS-PPP uses precise GPS orbit and clock products provided by the IGS. The solutions of PPP coordinates are represented in both NAD83 and ITRF14 data with detailed graphical analysis reports. This service has actively processed GLONASS data from October 4, 2011 and accepted userprovided ocean tidal loading (OTL) correction files from February 14, 2012.

#### **3.2. GAPS: GPS analysis and positioning software**

GPS analysis and positioning software (GAPS) is a web-based processing service for GPS observations provided by the University of New Brunswick (UNB). It is a service that does not require membership registration. This service uses IGS's rapid and final orbit and clock products during the process of GPS observations. GAPS is a service that delivers GNSS solutions to users via e-mail. The coordinate solutions of GAPS are represented in ITRF14 datum.

#### **3.3. APPS: automatic precise positioning service**

Automatic precise positioning service (APPS) is a web-based GPS evaluation service operated by NASA Jet Propulsion Laboratory (JPL) and the California Institute of Technology. In the background of this service, the scientific software GIPSY/OASIS II developed in this institution is also run. The system also uses real-time, daily and weekly GPS orbit and clock products produced by JPL. The results of the evaluation can be obtained shortly after the options in the service interface (antenna height, antenna type, e-mail address, etc.) are checked and the GNSS observations are loaded. The solutions of PPP coordinates are represented in ITRF08 datum with detailed analysis reports. APPS is a web-based positioning service that requires membership and offers the use of ftp services for industrial users.

was selected for the accuracy analysis. The GPS data segmented into 1-, 2-, 6-, 12-, and 24-h sessions were collected by HRUH station in static mode on April 18, 2018 (DOY 108). The data sampling interval of the GNSS receiver was 30 s. As a result of this study, we have compared the analysis results obtained by using CSRS-PPP, GAPS, APPS, MagicGNSS services, and scientific software (GIPSY/OASIS II) which produce solutions based on PPP technique. All services including GIPSY/OASIS II scientific software (except APPS) use coordinate solutions at ITRF14 datum. In order to be able to compare the analysis results of all services in the same datum, APPS coordinate solutions in ITRF08 datum have been converted to the coordinates of ITRF14 datum with the help of URL [7]. **Table 3** gives the coordinates and standard deviation results in the Cartesian coordinate system according to the 1-, 2-, 6-, 12-, and 24-h GPS

*X(m) Y(m) Z(m) σX*(*m*) *σY*(*m*) *σZ*(*m*)

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0.0460 0.0386 0.0347

0.0065 0.0065 0.0060

0.0035 0.0031 0.0031

0.0025 0.0022 0.0023

0.0018 0.0015 0.0016

1 h 3,954,667.2472 3,202,680.8771 3,833,020.8337

2 h 3,954,667.2465 3,202,680.8640 3,833,020.8351

6 h 3,954,667.2430 3,202,680.8621 3,833,020.8269

12 h 3,954,667.2426 3,202,680.8609 3,833,020.8263

24 h 3,954,667.2418 3,202,680.8605 3,833,020.8310

**Table 3.** HRUH station hourly coordinates and standard deviations.

The aim of the study was to determine how consistent results from web-based positioning services are. GPS observations for 1-, 2-, 6,- 12-, and 24-h on the same day (DOY 108) belonging to the same station were separated and loaded into each individual web-based positioning system and results were obtained. Apart from the results obtained during the 1-h observation period, the best coordinate precision and accuracy are understood from the results of the APPS service. The consistency between the GIPSY/OASIS II scientific software and the solutions of the GAPS web-based positioning systems is close together. MagicGNSS service provides only the coordinate points, the related standard deviations are not added to the figures. **Figures 2**–**6** show the results of the coordinates and standard deviation values of the Cartesian coordinate system for 1-, 2-, 6-, 12-, and 24-h GPS observations of the HRUH

When the solutions of 1-h GPS observations of the HRUH station in **Figure 2** are examined, the standard deviation values for the CSRS-PPP, GAPS, APPS, and GIPSY/OASIS II coordinate solutions range from 0.01 to 0.1 m. Standard deviation values of the coordinate components

observations of the HRUH station with GIPSY/OASIS II scientific software.

**HRUH GNSS station Observation duration**

station produced by the web-based positioning services, respectively.

#### **3.4. MagicGNSS: magic precise point positioning solution**

Magic Precise Point Positioning Solution is an Internet service created by Spanish GMV Company. MagicGNSS is a positioning service that uses accurate positioning detection technology. The most important advantage of the service is that it can analyze GPS and GLONASS observations together. This system can process both static and kinematic observations. The PPP module of this service uses accurate clock and precise orbit products which are provided by the IGS. The system supports RINEX and all compressed observation formats and offers free 1-GB disk space for member users. The service provides users with a detailed graphical analysis report along with positioning solutions. The solutions of PPP methods are represented in both ETRS89 and ITRF14 data. The service works by downloading or e-mailing the result files from the service's Internet interface.

#### **4. Experimental study**

This study provides the accuracy analysis of the web-based online services using PPP solution approaches. For this purpose, HRUH permanent reference station which located on top of the roof of Geomatics Engineering Department's GNSS Laboratory in Harran University Evaluation of GNSS Data with Internet Based Services: The Case of HRUH Station http://dx.doi.org/10.5772/intechopen.79064 79

**Table 3.** HRUH station hourly coordinates and standard deviations.

from single- or dual-frequency receivers based on static or PPP techniques. CSRS-PPP uses precise GPS orbit and clock products provided by the IGS. The solutions of PPP coordinates are represented in both NAD83 and ITRF14 data with detailed graphical analysis reports. This service has actively processed GLONASS data from October 4, 2011 and accepted user-

GPS analysis and positioning software (GAPS) is a web-based processing service for GPS observations provided by the University of New Brunswick (UNB). It is a service that does not require membership registration. This service uses IGS's rapid and final orbit and clock products during the process of GPS observations. GAPS is a service that delivers GNSS solutions to users via e-mail. The coordinate solutions of GAPS are represented in ITRF14 datum.

Automatic precise positioning service (APPS) is a web-based GPS evaluation service operated by NASA Jet Propulsion Laboratory (JPL) and the California Institute of Technology. In the background of this service, the scientific software GIPSY/OASIS II developed in this institution is also run. The system also uses real-time, daily and weekly GPS orbit and clock products produced by JPL. The results of the evaluation can be obtained shortly after the options in the service interface (antenna height, antenna type, e-mail address, etc.) are checked and the GNSS observations are loaded. The solutions of PPP coordinates are represented in ITRF08 datum with detailed analysis reports. APPS is a web-based positioning service that requires

Magic Precise Point Positioning Solution is an Internet service created by Spanish GMV Company. MagicGNSS is a positioning service that uses accurate positioning detection technology. The most important advantage of the service is that it can analyze GPS and GLONASS observations together. This system can process both static and kinematic observations. The PPP module of this service uses accurate clock and precise orbit products which are provided by the IGS. The system supports RINEX and all compressed observation formats and offers free 1-GB disk space for member users. The service provides users with a detailed graphical analysis report along with positioning solutions. The solutions of PPP methods are represented in both ETRS89 and ITRF14 data. The service works by downloading or e-mailing the

This study provides the accuracy analysis of the web-based online services using PPP solution approaches. For this purpose, HRUH permanent reference station which located on top of the roof of Geomatics Engineering Department's GNSS Laboratory in Harran University

provided ocean tidal loading (OTL) correction files from February 14, 2012.

**3.2. GAPS: GPS analysis and positioning software**

78 Accuracy of GNSS Methods

**3.3. APPS: automatic precise positioning service**

membership and offers the use of ftp services for industrial users.

**3.4. MagicGNSS: magic precise point positioning solution**

result files from the service's Internet interface.

**4. Experimental study**

was selected for the accuracy analysis. The GPS data segmented into 1-, 2-, 6-, 12-, and 24-h sessions were collected by HRUH station in static mode on April 18, 2018 (DOY 108). The data sampling interval of the GNSS receiver was 30 s. As a result of this study, we have compared the analysis results obtained by using CSRS-PPP, GAPS, APPS, MagicGNSS services, and scientific software (GIPSY/OASIS II) which produce solutions based on PPP technique. All services including GIPSY/OASIS II scientific software (except APPS) use coordinate solutions at ITRF14 datum. In order to be able to compare the analysis results of all services in the same datum, APPS coordinate solutions in ITRF08 datum have been converted to the coordinates of ITRF14 datum with the help of URL [7]. **Table 3** gives the coordinates and standard deviation results in the Cartesian coordinate system according to the 1-, 2-, 6-, 12-, and 24-h GPS observations of the HRUH station with GIPSY/OASIS II scientific software.

The aim of the study was to determine how consistent results from web-based positioning services are. GPS observations for 1-, 2-, 6,- 12-, and 24-h on the same day (DOY 108) belonging to the same station were separated and loaded into each individual web-based positioning system and results were obtained. Apart from the results obtained during the 1-h observation period, the best coordinate precision and accuracy are understood from the results of the APPS service. The consistency between the GIPSY/OASIS II scientific software and the solutions of the GAPS web-based positioning systems is close together. MagicGNSS service provides only the coordinate points, the related standard deviations are not added to the figures. **Figures 2**–**6** show the results of the coordinates and standard deviation values of the Cartesian coordinate system for 1-, 2-, 6-, 12-, and 24-h GPS observations of the HRUH station produced by the web-based positioning services, respectively.

When the solutions of 1-h GPS observations of the HRUH station in **Figure 2** are examined, the standard deviation values for the CSRS-PPP, GAPS, APPS, and GIPSY/OASIS II coordinate solutions range from 0.01 to 0.1 m. Standard deviation values of the coordinate components

**Figure 2.** Standard deviations of HRUH station coordinates (1 h).

obtained from the CSRS-PPP service were determined as σx = ±0.092 m, σy = ±0.079 m, and σz = ±0.071 m, respectively. Standard deviation values of the coordinate components obtained from the GAPS service are σx = ±0.021 m, σy = ±0.033 m, and σz = ±0.026 m, respectively, and the standard deviation values of the coordinate components obtained from the APPS service are σx = ±0.038 m, σy = ±0.033 m, and σz = ±0.026 m. Standard deviation values of the coordinate components obtained by GIPSY/OASIS II scientific software are calculated as σx = ±0.046 m, σy = ±0.038 m, and σz = ±0.034 m, respectively.

When the solutions of the 2-h GPS observations of the HRUH station in **Figure 3** are examined, the standard deviation values of the CSRS-PPP, GAPS, APPS, and GIPSY/OASIS II coordinate solutions range from 0.005 to 0.056 m. Standard deviation values of the coordinate components obtained from the CSRS-PPP service were determined as σx = ±0.056 m, σy = ±0.035 m, and σz = ±0.037 m, respectively. Standard deviation values of coordinate components obtained from GAPS service are σx = ±0.014 m, σy = ±0.006 m, and σz = ±0.008 m, respectively and the standard deviation values of coordinate components obtained from APPS service are σx = ±0.005 m, σy = ±0.005 m, and σz = ±0.005 m. Standard deviation values of the coordinate components obtained by GIPSY/OASIS II scientific software were calculated as σx = ±0.006 m, σy = ±0.006 m, and σz = ±0.006 m, respectively.

When the solutions of the 6-h GPS observations of the HRUH station in **Figure 4** are examined, the standard deviation values for the CSRS-PPP, GAPS, APPS, and GIPSY/OASIS II coordinate solutions range from 0.002 to 0.027 m. Standard deviation values of the coordinate components obtained from CSRS-PPP service were determined as σx = ±0.027m, σy = ±0.017m, and σz = ±0.018m, respectively. Standard deviation values of coordinate components obtained from GAPS service are σx = ±0.005 m, σy = ±0.003 m, and σz = ±0.003 m, respectively, and the standard deviation values of coordinate components obtained from APPS service are σx = ±0.003 m, σy = ±0.003 m, and σz = ±0.003 m. Standard deviation values of the coordinate components obtained by GIPSY/OASIS II scientific software were calculated as σx = ±0.003 m, σy = ±0.003 m, and σz = ±0.003 m, respectively.

When the solutions of the 12-h GPS observations of the HRUH station are examined in **Figure 5**, the standard deviation values of the CSRS-PPP, GAPS, APPS, and GIPSY/OASIS II coordinate solutions range from 0.002 to 0.015 m. Standard deviation values of the coordinate components obtained from the CSRS-PPP service were determined as σx = ±0.0147 m, σy = ±0.0128 m, and σz = ±0.0125 m, respectively. Standard deviation values of coordinate components obtained from GAPS service are σx = ±0.0026 m, σy = ±0.0024 m, and σz = ±0.0021 m,

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**Figure 3.** Standard deviations of HRUH station coordinates (2 h).

**Figure 4.** Standard deviations of HRUH station coordinates (6 h).

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**Figure 3.** Standard deviations of HRUH station coordinates (2 h).

obtained from the CSRS-PPP service were determined as σx = ±0.092 m, σy = ±0.079 m, and σz = ±0.071 m, respectively. Standard deviation values of the coordinate components obtained from the GAPS service are σx = ±0.021 m, σy = ±0.033 m, and σz = ±0.026 m, respectively, and the standard deviation values of the coordinate components obtained from the APPS service are σx = ±0.038 m, σy = ±0.033 m, and σz = ±0.026 m. Standard deviation values of the coordinate components obtained by GIPSY/OASIS II scientific software are calculated as σx = ±0.046 m,

When the solutions of the 2-h GPS observations of the HRUH station in **Figure 3** are examined, the standard deviation values of the CSRS-PPP, GAPS, APPS, and GIPSY/OASIS II coordinate solutions range from 0.005 to 0.056 m. Standard deviation values of the coordinate components obtained from the CSRS-PPP service were determined as σx = ±0.056 m, σy = ±0.035 m, and σz = ±0.037 m, respectively. Standard deviation values of coordinate components obtained from GAPS service are σx = ±0.014 m, σy = ±0.006 m, and σz = ±0.008 m, respectively and the standard deviation values of coordinate components obtained from APPS service are σx = ±0.005 m, σy = ±0.005 m, and σz = ±0.005 m. Standard deviation values of the coordinate components obtained by GIPSY/OASIS II scientific software were calculated as σx = ±0.006 m,

When the solutions of the 6-h GPS observations of the HRUH station in **Figure 4** are examined, the standard deviation values for the CSRS-PPP, GAPS, APPS, and GIPSY/OASIS II coordinate solutions range from 0.002 to 0.027 m. Standard deviation values of the coordinate components obtained from CSRS-PPP service were determined as σx = ±0.027m, σy = ±0.017m, and σz = ±0.018m, respectively. Standard deviation values of coordinate components obtained from GAPS service are σx = ±0.005 m, σy = ±0.003 m, and σz = ±0.003 m, respectively, and the standard deviation values of coordinate components obtained from APPS service are σx = ±0.003 m, σy = ±0.003 m, and σz = ±0.003 m. Standard deviation values of the coordinate components obtained by GIPSY/OASIS II scientific software were calculated as σx = ±0.003 m, σy = ±0.003 m, and σz = ±0.003 m, respectively.

σy = ±0.038 m, and σz = ±0.034 m, respectively.

**Figure 2.** Standard deviations of HRUH station coordinates (1 h).

80 Accuracy of GNSS Methods

σy = ±0.006 m, and σz = ±0.006 m, respectively.

**Figure 4.** Standard deviations of HRUH station coordinates (6 h).

When the solutions of the 12-h GPS observations of the HRUH station are examined in **Figure 5**, the standard deviation values of the CSRS-PPP, GAPS, APPS, and GIPSY/OASIS II coordinate solutions range from 0.002 to 0.015 m. Standard deviation values of the coordinate components obtained from the CSRS-PPP service were determined as σx = ±0.0147 m, σy = ±0.0128 m, and σz = ±0.0125 m, respectively. Standard deviation values of coordinate components obtained from GAPS service are σx = ±0.0026 m, σy = ±0.0024 m, and σz = ±0.0021 m,

**Figure 5.** Standard deviations of HRUH station coordinates (12 h).

respectively, and the standard deviation values of coordinate components obtained from APPS service are σx = ±0.0022 m, σy = ±0.0019 m, and σz = ±0.0019 m. Standard deviation values of the coordinate components obtained by GIPSY/OASIS II scientific software are calculated as σx = ±0.0025 m, σy = ±0.0022 m, and σz = ±0.0023 m, respectively.

When the solutions of the 24-h GPS observations of the HRUH station are examined in **Figure 6**, the standard deviation values of the CSRS-PPP, GAPS, APPS, and GIPSY/OASIS II coordinate solutions range from 0.001 to 0.009 m. Standard deviation values of the coordinate components obtained from CSRS-PPP service were determined as σx = ±0.0096 m, σy = ±0.0086 m, and σz = ±0.0084 m, respectively. Standard deviation values of coordinate components obtained from GAPS service are σx = ±0.0017 m, σy = ±0.0015 m, and σz = ±0.0015 m, respectively, and the standard deviation values of coordinate components obtained from APPS service are σx = ±0.0015 m, σy = ±0.0013 m, and σz = ±0.0014 m. Standard deviation values of the coordinate components obtained by GIPSY/OASIS II scientific software are calculated as σx = ±0.0018 m, σy = ±0.0015 m, and σz = ±0.0016 m, respectively.

If the result in **Figures 2**–**6** will be interpreted graphically, the most sensitive results for the results of different observation periods of each coordinate component evaluated in the webbased positioning services are GAPS service for 1 h observation period; APPS service for 2-, 6-, 12-, and 24-h observation periods. The CSRS-PPP service was at the forefront of all evaluations.

After obtaining the standard deviations of each coordinate component in the Cartesian coordinate system of the web-based positioning services, the obtained coordinates were compared with the coordinates obtained in GIPSY/OASIS II scientific software. The calculated web-based coordinate results were subtracted from the coordinates obtained from GIPSY/ OASIS II scientific software and classified according to web-based positioning services and GPS observation times (**Figures 7**–**10**).

In **Figure 7**, the differences between the CSRS-PPP web-based positioning service and the coordinate solutions of different GPS observation times obtained by the GIPSY/OASIS II scientific software are calculated. The differences of the coordinate solutions of 1 h GPS observation time are calculated as ΔX = 0.039 m, ΔY = 0.095 m, and ΔZ = 0.115 m. The differences of the coordinate solutions of the 2-h GPS observation time were calculated as ΔX = −0.020 m, ΔY = 0.091 m, and ΔZ = 0.058 m. The differences of the coordinate solutions of the 6-h GPS observation

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**Figure 7.** Coordinate differences between CSRS-PPP solution and GIPSY/OASIS II solution.

**Figure 6.** Standard deviations of HRUH station coordinates (24 h).

Evaluation of GNSS Data with Internet Based Services: The Case of HRUH Station http://dx.doi.org/10.5772/intechopen.79064 83

**Figure 6.** Standard deviations of HRUH station coordinates (24 h).

respectively, and the standard deviation values of coordinate components obtained from APPS service are σx = ±0.0022 m, σy = ±0.0019 m, and σz = ±0.0019 m. Standard deviation values of the coordinate components obtained by GIPSY/OASIS II scientific software are calculated

When the solutions of the 24-h GPS observations of the HRUH station are examined in **Figure 6**, the standard deviation values of the CSRS-PPP, GAPS, APPS, and GIPSY/OASIS II coordinate solutions range from 0.001 to 0.009 m. Standard deviation values of the coordinate components obtained from CSRS-PPP service were determined as σx = ±0.0096 m, σy = ±0.0086 m, and σz = ±0.0084 m, respectively. Standard deviation values of coordinate components obtained from GAPS service are σx = ±0.0017 m, σy = ±0.0015 m, and σz = ±0.0015 m, respectively, and the standard deviation values of coordinate components obtained from APPS service are σx = ±0.0015 m, σy = ±0.0013 m, and σz = ±0.0014 m. Standard deviation values of the coordinate components obtained by GIPSY/OASIS II scientific software are calculated

If the result in **Figures 2**–**6** will be interpreted graphically, the most sensitive results for the results of different observation periods of each coordinate component evaluated in the webbased positioning services are GAPS service for 1 h observation period; APPS service for 2-, 6-, 12-, and 24-h observation periods. The CSRS-PPP service was at the forefront of all evaluations. After obtaining the standard deviations of each coordinate component in the Cartesian coordinate system of the web-based positioning services, the obtained coordinates were compared with the coordinates obtained in GIPSY/OASIS II scientific software. The calculated web-based coordinate results were subtracted from the coordinates obtained from GIPSY/ OASIS II scientific software and classified according to web-based positioning services and

as σx = ±0.0025 m, σy = ±0.0022 m, and σz = ±0.0023 m, respectively.

**Figure 5.** Standard deviations of HRUH station coordinates (12 h).

82 Accuracy of GNSS Methods

as σx = ±0.0018 m, σy = ±0.0015 m, and σz = ±0.0016 m, respectively.

GPS observation times (**Figures 7**–**10**).

**Figure 7.** Coordinate differences between CSRS-PPP solution and GIPSY/OASIS II solution.

In **Figure 7**, the differences between the CSRS-PPP web-based positioning service and the coordinate solutions of different GPS observation times obtained by the GIPSY/OASIS II scientific software are calculated. The differences of the coordinate solutions of 1 h GPS observation time are calculated as ΔX = 0.039 m, ΔY = 0.095 m, and ΔZ = 0.115 m. The differences of the coordinate solutions of the 2-h GPS observation time were calculated as ΔX = −0.020 m, ΔY = 0.091 m, and ΔZ = 0.058 m. The differences of the coordinate solutions of the 6-h GPS observation

**Figure 8.** Coordinate differences between GAPS solution and GIPSY/OASIS II solution.

period were calculated as ΔX = −0.001 m, ΔY = 0.074 m, and ΔZ = 0.049 m. The differences of the coordinate solutions of the 12-h GPS observation period were calculated as ΔX = 0.031 m, ΔY = 0.058 m, and ΔZ = 0.058 m. The differences of the coordinate solutions for the 24-h GPS observation period were calculated as ΔX = 0.042 m, ΔY = 0.052 m, and ΔZ = 0.053 m.

In **Figure 8**, the differences between the GAPS web-based positioning service and the coordinate solutions of different GPS observation times obtained by the GIPSY/OASIS II scientific software are calculated. The differences of the coordinate solutions of the 1 h GPS observation period were calculated as ΔX = 0.033 m, ΔY = 0.019 m, and ΔZ = 0.045 m. The differences in coordinate solutions for the 2-h GPS observation period were calculated as ΔX = 0.058 m, ΔY = 0.034 m, and ΔZ = 0.064 m. The differences of the coordinate solutions of the 6-h GPS observation period were calculated as ΔX = 0.037 m, ΔY = 0.032 m, and ΔZ = 0.057 m. The differences of the coordinate solutions of the 12-h GPS observation period were calculated as ΔX = 0.033 m, ΔY = 0.030 m, and ΔZ = 0.053 m. The differences of coordinate solutions for the 24-h GPS observation period were calculated as ΔX = 0.039 m, ΔY = 0.039 m, and ΔZ = 0.053 m.

In **Figure 9**, the differences between the coordinate solutions of different GPS observation times obtained by the APPS web-based positioning service and GIPSY/OASIS II scientific software are calculated. The differences of the coordinate solutions of 1 h GPS observation time are calculated as ΔX = 0.050 m, ΔY = 0.008 m, and ΔZ = 0.039 m. The differences of the coordinate solutions of the 2-h GPS observation period were calculated as ΔX = 0.054 m, ΔY = 0.040 m, and ΔZ = 0.055 m. The differences of the coordinate solutions of the 6-h GPS observation period were calculated as ΔX = 0.052 m, ΔY = 0.042 m, and ΔZ = 0.054 m. The differences of the coordinate solutions for the 12-h GPS observation period were calculated as ΔX = 0.048 m, ΔY = 0.039 m, and ΔZ = 0.052 m. The differences in the coordinate solutions of the 24-h GPS observation period were calculated as ΔX = 0.048 m, ΔY = 0.040 m, and ΔZ = 0.053 m.

In **Figure 10** the differences between the coordinate solutions of different GPS observation times obtained by the MagicGNSS web-based positioning service and GIPSY-OASIS scientific software are calculated. The differences of the coordinate solutions of 1 h GPS observation time are calculated as ΔX = 0.026 m, ΔY = 0.033 m, and ΔZ = 0.013 m. The differences of coordinate solutions for the 2-h GPS observation time are calculated as ΔX = 0.035 m, ΔY = 0.026 m,

**Figure 10.** Coordinate differences between MagicGNSS solution and GIPSY/OASIS II solution.

**Figure 9.** Coordinate differences between APPS solution and GIPSY/OASIS II solution.

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**Figure 9.** Coordinate differences between APPS solution and GIPSY/OASIS II solution.

**Figure 8.** Coordinate differences between GAPS solution and GIPSY/OASIS II solution.

84 Accuracy of GNSS Methods

period were calculated as ΔX = −0.001 m, ΔY = 0.074 m, and ΔZ = 0.049 m. The differences of the coordinate solutions of the 12-h GPS observation period were calculated as ΔX = 0.031 m, ΔY = 0.058 m, and ΔZ = 0.058 m. The differences of the coordinate solutions for the 24-h GPS

In **Figure 8**, the differences between the GAPS web-based positioning service and the coordinate solutions of different GPS observation times obtained by the GIPSY/OASIS II scientific software are calculated. The differences of the coordinate solutions of the 1 h GPS observation period were calculated as ΔX = 0.033 m, ΔY = 0.019 m, and ΔZ = 0.045 m. The differences in coordinate solutions for the 2-h GPS observation period were calculated as ΔX = 0.058 m, ΔY = 0.034 m, and ΔZ = 0.064 m. The differences of the coordinate solutions of the 6-h GPS observation period were calculated as ΔX = 0.037 m, ΔY = 0.032 m, and ΔZ = 0.057 m. The differences of the coordinate solutions of the 12-h GPS observation period were calculated as ΔX = 0.033 m, ΔY = 0.030 m, and ΔZ = 0.053 m. The differences of coordinate solutions for the 24-h GPS observation period were calculated as ΔX = 0.039 m, ΔY = 0.039 m, and ΔZ = 0.053 m. In **Figure 9**, the differences between the coordinate solutions of different GPS observation times obtained by the APPS web-based positioning service and GIPSY/OASIS II scientific software are calculated. The differences of the coordinate solutions of 1 h GPS observation time are calculated as ΔX = 0.050 m, ΔY = 0.008 m, and ΔZ = 0.039 m. The differences of the coordinate solutions of the 2-h GPS observation period were calculated as ΔX = 0.054 m, ΔY = 0.040 m, and ΔZ = 0.055 m. The differences of the coordinate solutions of the 6-h GPS observation period were calculated as ΔX = 0.052 m, ΔY = 0.042 m, and ΔZ = 0.054 m. The differences of the coordinate solutions for the 12-h GPS observation period were calculated as ΔX = 0.048 m, ΔY = 0.039 m, and ΔZ = 0.052 m. The differences in the coordinate solutions of the 24-h GPS

observation period were calculated as ΔX = 0.042 m, ΔY = 0.052 m, and ΔZ = 0.053 m.

observation period were calculated as ΔX = 0.048 m, ΔY = 0.040 m, and ΔZ = 0.053 m.

**Figure 10.** Coordinate differences between MagicGNSS solution and GIPSY/OASIS II solution.

In **Figure 10** the differences between the coordinate solutions of different GPS observation times obtained by the MagicGNSS web-based positioning service and GIPSY-OASIS scientific software are calculated. The differences of the coordinate solutions of 1 h GPS observation time are calculated as ΔX = 0.026 m, ΔY = 0.033 m, and ΔZ = 0.013 m. The differences of coordinate solutions for the 2-h GPS observation time are calculated as ΔX = 0.035 m, ΔY = 0.026 m, and ΔZ = 0.037 m. The differences of the coordinate solutions of the 6-h GPS observation period were calculated as ΔX = 0.036 m, ΔY = 0.026 m, and ΔZ = 0.045 m. The differences in coordinate solutions for the 12-h GPS observation period were calculated as ΔX = 0.035 m, ΔY = 0.028 m, and ΔZ = 0.045 m. The differences of the coordinate solutions of the 24-h GPS observation period were calculated as ΔX = 0.035 m, ΔY = 0.038 m, and ΔZ = 0.043 m.

evaluated according to the PPP technique is directly related to the accuracy of the IGS orbit

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In such systems, many outcome products can be obtained without the need for GNSS expertise other than basic level. When using web-based positioning services, choosing the solution parameters appropriate to the data structure and the measurement method can bring the coordinate accuracy to the highest level. Applications for scientific research should indicate that such services are not suitable for applications that require expertise, such as ionospheric and tropospheric models, deformation analysis studies, earth orienta-

The results from web-based location services show that there is not much difference between the results of software that solves with scientific PPP technique when there is enough observation period in GNSS sessions. This is rather obvious in the precision results given in **Figures 2**–**6**. In the application where PPP services are evaluated, it is seen that the results are directly related to the observation period. Accuracy is increased by increasing the observation time from 1 to 24 h, but the results are still at several centimeters. Precision results given in **Figures 2**–**6** are very similar to those published by the IGS. In order to be able to obtain accuracy results similar to those of precision results, one needs to adopt equal processing strategy for all software used here but unfortunately this was impossible

The user needs to select the observation period on the point according to the expected accuracy level. The results obtained from such services, which provide a great gain in terms of time and cost, are sufficient to give the position information for many engineering applications.

The author thanks to International GNSS Service (IGS) for product supports, and to organizations, which present web-based online services (CSRS-PPP, GAPS, APPS, MagicGNSS). Special thanks to Research Assistants Ali Hasan DOĞAN and Mustafa Fahri KARABULUT in Yildiz Technical University (YTU) for their help in assisting at the post processing stage of GPS observations by using GIPSY-OASIS II scientific software with PPP technique. NASA JPL's software GIPSY/OASIS II is licensed to Department of Geomatic Engineering of YTU.

and clock information.

tion parameters, and so on.

throughout this study.

**Acknowledgements**

**Author details**

Mustafa Ulukavak

Address all correspondence to<EMAIL_ADDRESS>
Harran University, Sanliurfa, Turkey

APPS uses GIPSY/OASIS II in the background. However, the difference in the results between GIPSY/OASIS II and APPS is slightly larger than the difference in results between GIPSY/ OASIS II and MagicGNSS. This can be ascribed to the fact that APPS results are based on the ITRF08 but not the ITRF14 on which both GIPSY/OASIS II and MagicGNSS rely.

In **Figures 7**–**10**, the differences between the coordinate values of the HRUH permanent GNSS station produced by the web-based positioning services for different GPS observation times and the coordinate solutions obtained by the GIPSY/OASIS II scientific software are examined.

In **Figure 7**, when the coordinate solutions obtained from the CSRS-PPP web-based positioning service are compared with the coordinate solutions obtained from the GIPSY/OASIS II scientific software, the coordinate differences between 1- and 2-h observation periods are found to be around 10 cm, coordinate differences for 6- and 12-h observation periods are around 5 cm, and for 24-h observation periods, coordinate differences are less than 5 cm.

In **Figure 8**, when the coordinate solutions obtained from the GAPS web-based positioning service are compared with the coordinate solutions obtained from the GIPSY/OASIS II scientific software, the coordinate differences between 1-h observation period is found to be less than 5 cm, coordinate differences for 2-, 6-, 12-, and 24-h observation periods are around 5 cm.

In **Figure 9**, when the coordinate solutions obtained from the APPS web-based positioning service are compared with the coordinate solutions obtained from the GIPSY/OASIS II scientific software, the coordinate differences between 1-h observation period is found to be less than 5 cm, coordinate differences for 2-, 6-, 12-, and 24-h observation periods are around 5 cm.

In **Figure 10**, when the coordinate solutions obtained from the MagicGNSS web-based positioning service are compared with the coordinate solutions obtained from the GIPSY/OASIS II scientific software, the coordinate differences between 1-, 2-, 6-, 12-, and 24-h observation period is found to be less than 5 cm.

#### **5. Conclusion**

Today, PPP technology is becoming increasingly important. With its many advantages, it poses a serious alternative to positioning methods. However, the use of web-based positioning services, which analyze using PPP technology, is becoming widespread. The PPP technique is feasible in the measurement and evaluation process with only one GNSS receiver, and providing these services to the user free of charge on the Internet makes these systems advantageous in many applications. It should not be forgotten that the reliability of the results evaluated according to the PPP technique is directly related to the accuracy of the IGS orbit and clock information.

In such systems, many outcome products can be obtained without the need for GNSS expertise other than basic level. When using web-based positioning services, choosing the solution parameters appropriate to the data structure and the measurement method can bring the coordinate accuracy to the highest level. Applications for scientific research should indicate that such services are not suitable for applications that require expertise, such as ionospheric and tropospheric models, deformation analysis studies, earth orientation parameters, and so on.

The results from web-based location services show that there is not much difference between the results of software that solves with scientific PPP technique when there is enough observation period in GNSS sessions. This is rather obvious in the precision results given in **Figures 2**–**6**. In the application where PPP services are evaluated, it is seen that the results are directly related to the observation period. Accuracy is increased by increasing the observation time from 1 to 24 h, but the results are still at several centimeters. Precision results given in **Figures 2**–**6** are very similar to those published by the IGS. In order to be able to obtain accuracy results similar to those of precision results, one needs to adopt equal processing strategy for all software used here but unfortunately this was impossible throughout this study.

The user needs to select the observation period on the point according to the expected accuracy level. The results obtained from such services, which provide a great gain in terms of time and cost, are sufficient to give the position information for many engineering applications.

#### **Acknowledgements**

and ΔZ = 0.037 m. The differences of the coordinate solutions of the 6-h GPS observation period were calculated as ΔX = 0.036 m, ΔY = 0.026 m, and ΔZ = 0.045 m. The differences in coordinate solutions for the 12-h GPS observation period were calculated as ΔX = 0.035 m, ΔY = 0.028 m, and ΔZ = 0.045 m. The differences of the coordinate solutions of the 24-h GPS

APPS uses GIPSY/OASIS II in the background. However, the difference in the results between GIPSY/OASIS II and APPS is slightly larger than the difference in results between GIPSY/ OASIS II and MagicGNSS. This can be ascribed to the fact that APPS results are based on the

In **Figures 7**–**10**, the differences between the coordinate values of the HRUH permanent GNSS station produced by the web-based positioning services for different GPS observation times and the coordinate solutions obtained by the GIPSY/OASIS II scientific software are examined. In **Figure 7**, when the coordinate solutions obtained from the CSRS-PPP web-based positioning service are compared with the coordinate solutions obtained from the GIPSY/OASIS II scientific software, the coordinate differences between 1- and 2-h observation periods are found to be around 10 cm, coordinate differences for 6- and 12-h observation periods are around

In **Figure 8**, when the coordinate solutions obtained from the GAPS web-based positioning service are compared with the coordinate solutions obtained from the GIPSY/OASIS II scientific software, the coordinate differences between 1-h observation period is found to be less than 5 cm, coordinate differences for 2-, 6-, 12-, and 24-h observation periods are around 5 cm. In **Figure 9**, when the coordinate solutions obtained from the APPS web-based positioning service are compared with the coordinate solutions obtained from the GIPSY/OASIS II scientific software, the coordinate differences between 1-h observation period is found to be less than 5 cm, coordinate differences for 2-, 6-, 12-, and 24-h observation periods are around 5 cm. In **Figure 10**, when the coordinate solutions obtained from the MagicGNSS web-based positioning service are compared with the coordinate solutions obtained from the GIPSY/OASIS II scientific software, the coordinate differences between 1-, 2-, 6-, 12-, and 24-h observation

Today, PPP technology is becoming increasingly important. With its many advantages, it poses a serious alternative to positioning methods. However, the use of web-based positioning services, which analyze using PPP technology, is becoming widespread. The PPP technique is feasible in the measurement and evaluation process with only one GNSS receiver, and providing these services to the user free of charge on the Internet makes these systems advantageous in many applications. It should not be forgotten that the reliability of the results

observation period were calculated as ΔX = 0.035 m, ΔY = 0.038 m, and ΔZ = 0.043 m.

ITRF08 but not the ITRF14 on which both GIPSY/OASIS II and MagicGNSS rely.

5 cm, and for 24-h observation periods, coordinate differences are less than 5 cm.

period is found to be less than 5 cm.

**5. Conclusion**

86 Accuracy of GNSS Methods

The author thanks to International GNSS Service (IGS) for product supports, and to organizations, which present web-based online services (CSRS-PPP, GAPS, APPS, MagicGNSS). Special thanks to Research Assistants Ali Hasan DOĞAN and Mustafa Fahri KARABULUT in Yildiz Technical University (YTU) for their help in assisting at the post processing stage of GPS observations by using GIPSY-OASIS II scientific software with PPP technique. NASA JPL's software GIPSY/OASIS II is licensed to Department of Geomatic Engineering of YTU.

#### **Author details**

Mustafa Ulukavak Address all correspondence to<EMAIL_ADDRESS>Harran University, Sanliurfa, Turkey

### **References**

[1] Ghoddousi-Fard R, Dare P. Online GPS processing services: An initial study. GPS Solutions. 2006;**10**:12-20. DOI: 10.1007/s10291-005-0147-5

**Chapter 6**

Provisional chapter

**Comparative Study of Some Online GNSS Post-**

Comparative Study of Some Online GNSS Post-

Olalekan Adekunle Isioye, Mefe Moses and

Olalekan Adekunle Isioye, Mefe Moses

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79924

**in Nigeria**

in Nigeria

Lukman Abdulmumin

Abstract

accuracy

and Lukman Abdulmumin

**Processing Services at Selected Permanent GNSS Sites**

DOI: 10.5772/intechopen.79924

Many applications in surveying and mapping have been made simpler and more precise due to the advent of GNSS, and thus, the demand for using cutting-edge GNSS techniques in surveying and mapping applications has become indispensable. Online GNSS postprocessing services are now available to provide support for users in need of precise point positioning or conventional differential positioning services and without requiring a prior knowledge of GNSS processing software. This study evaluates the performance of some online GNSS facilities with emphasis on observation duration (i.e. 1hr, 2hr, 6hr 12hr and 24hr observations). Three of these online facilities (AUSPOS, GAPS and magic-GNSS) were chosen based on their mode of operation and were evaluated at the location of five permanent GNSS stations in Nigeria. The study cut across two epochs in the year 2014 (i.e. seven days each in the months of January and July). Results in this study indicate that users can expect reliable results from these online services and their accuracy is within allowable limits for mapping applications in Nigeria. The similarity of the results between all of the services used is amazing, thus further demonstrates the robustness of the

Keywords: Global Navigation Satellite System (GNSS), continuously operating reference stations (CORS), precise point positioning (PPP), GNSS online processing, positioning

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

algorithms and processes employed by the different online facilities.

Processing Services at Selected Permanent GNSS Sites

#### **Comparative Study of Some Online GNSS Post-Processing Services at Selected Permanent GNSS Sites in Nigeria** Comparative Study of Some Online GNSS Post-Processing Services at Selected Permanent GNSS Sites in Nigeria

DOI: 10.5772/intechopen.79924

Olalekan Adekunle Isioye, Mefe Moses and Lukman Abdulmumin Olalekan Adekunle Isioye, Mefe Moses and Lukman Abdulmumin

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79924

#### Abstract

**References**

88 Accuracy of GNSS Methods

[1] Ghoddousi-Fard R, Dare P. Online GPS processing services: An initial study. GPS

[2] El-Mowafy A. Analysis of web-based GNSS post-processing services for static and kinematic positioning using short data spans. Survey Review. 2011;**43**:535-549. DOI: 10.1179

[3] Gakstatter E. A Comparison of Free GPS Online Post-Processing Services GPS World [Internet]. 2013. Available from: http://gpsworld.com/a-comparison-of-free-gps-online-

[4] Ocalan T, Erdogan B, Tunalioglu N. Analysis of web-based online services for GPS relative and precise point positioning techniques. Boletim de Ciências Geodésicas.

[5] Zumberge JF, Heflin MB, Jefferson DC, Watkins MM, Webb FH. Precise point positioning for the efficient and robust analysis of GPS data from large networks. Journal of

[6] Dach R, Hugentobler U, Fridez P, Meindl M. Manual of bernese GPS Software Version

[7] Transformation Parameters from ITRF08 to ITRF2014 [Internet]. 2018. Available from: http://itrf.ign.fr/doc\_ITRF/Transfo-ITRF2014\_ITRFs.txt [Accessed: Apr 28, 2018]

Solutions. 2006;**10**:12-20. DOI: 10.1007/s10291-005-0147-5

post-processing-services/ [Accessed: Apr 19, 2018]

2013;**19**(2):191-207. DOI: 10.1590/S1982-21702013000200003

5.0. University of Bern: Astronomical Institute; 2007. 612 p

Geophysical Research. 1997;**102**(3):5005-5017. DOI: 10.1029/96JB03860

/003962611X13117748892074

Many applications in surveying and mapping have been made simpler and more precise due to the advent of GNSS, and thus, the demand for using cutting-edge GNSS techniques in surveying and mapping applications has become indispensable. Online GNSS postprocessing services are now available to provide support for users in need of precise point positioning or conventional differential positioning services and without requiring a prior knowledge of GNSS processing software. This study evaluates the performance of some online GNSS facilities with emphasis on observation duration (i.e. 1hr, 2hr, 6hr 12hr and 24hr observations). Three of these online facilities (AUSPOS, GAPS and magic-GNSS) were chosen based on their mode of operation and were evaluated at the location of five permanent GNSS stations in Nigeria. The study cut across two epochs in the year 2014 (i.e. seven days each in the months of January and July). Results in this study indicate that users can expect reliable results from these online services and their accuracy is within allowable limits for mapping applications in Nigeria. The similarity of the results between all of the services used is amazing, thus further demonstrates the robustness of the algorithms and processes employed by the different online facilities.

Keywords: Global Navigation Satellite System (GNSS), continuously operating reference stations (CORS), precise point positioning (PPP), GNSS online processing, positioning accuracy

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited. © 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### 1. Introduction

Global Navigation Satellite Systems (GNSS) is generic term for a composition of different satellite navigation technologies such as American GPS (Global Positioning System); its Russian equivalent, GLONASS (GLObal Navigation Satellite System); the Chinese system, BeiDou; the Japanese regional system, QZSS; the Indian regional system IRNSS (Indian Regional Navigation Satellite System); finally, is the European Galileo system. The GPS and GLONASS has since attained full operational status. The BeiDou, is expected to achieve completion for worldwide service in 2020, although a limited version of its signal has already been available since December 2012. The QZSS, is at present providing a limited service in the form of an augmented signal for GPS, but should be progressively upgraded and achieve full impartiality in 2023. The IRNSS, is at a final point operation as well. The Galileo system is expected to attain full operational capability in 2020 [1, 2].

GNSS processing services. These services provide GNSS processing results to the user free of charge and with unlimited access. The user sends a Receiver Independent Exchange Format (RINEX) file to the service and within a short period of time, the estimated position of the receiver used to collect the RINEX data is sent back to the user. Organisations that provide these free services include: Geohazards Division of Geoscience Australia, the Geodetic Survey Division (GSD) in Canada, the United States' National Geodetic Survey (NGS), Scripps Orbit and Permanent Array Center (SOPAC) at the University of California and the Jet Propulsion

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The only requirement for using these services is a computer having an internet connection and web browser. These services are designed to be as simple as possible for the user and with minimal input. Users of such systems have to perform uploading/sending of their collected data in RINEX format by using the web site of these services, e-mail or ftp sites to the system and selecting a few processing options. Some of these services process not only the GPS but also the data of other systems, particularly those of GLONASS, and provide resilience and a