source can be modeled as cyclostationary Napolitano (2020). Pulsars have
already been successfully modeled as cyclostationary sources Demorest (2011).

The fraction-of-time distribution of the detected particles can exhibit
periodic or almost-periodic behavior. This behavior can be evidenced by first-
order cyclostationary analysis (Napolitano, 2019, Chapter 2).

###  6.3 The data ontology

The CREDO ambition concerning data quality and access policy is being
gradually implemented since the first unique data of scientific value were
recorded, stored in the CREDO central system and made public via web services,
i.e. since the middle of 2018. With the growing data set volume and with the
development and improvement of the data mining and interpretation tools, more
and more effort was dedicated to maintain the compatibility of the available
data with international standards. This effort is presently centered around
implementing solutions concerning the data ontology.

The CREDO project is already gathering and integrating detections data
originating from user’s devices running the CREDO Detector app, but also from
further sources, and further data, e.g. produced by processing and analysis.
One of the visions of CREDO is also to make this data available for
exploitation to the research community, but also to citizen scientists coming
from the general public. This goal is already partly fulfilled by the CREDO
data API described above. However, the current trend in open data publishing
is to make the data a first class web citizen by publishing it in semantic
formats on the Linked Open Data (LOD) Bizer et al. (2009) network333As of July
2020, the LOD network featured at least 1260 datasets from domains such as
geography, life sciences, linguistics, and many others, as documented by the
LOD Cloud lod .. For this, a suitable ontology (also sometimes called linked
data vocabulary) needs to be used, that provides semantic schema for the data.
Such ontologies are usually developed in OWL (Web Ontology Language) OWL  and
published on the web. The data is then translated in to the RDF (Resource
Description Framework) RDF  format using classes and properties defined in the
ontology. Larger datasets are often made accessible via SPARQL endpoints – web
interfaces by which users and applications may directly query the data using
the SPARQL querying language SPA .

The CREDO Ontology cre  is the first step towards making CREDO data available
through the LOD network. The CREDO ontology is a lightweight OWL ontology. The
current version features 20 classes, 14 object properties (that represent
relations between classes) and 40 data properties (that represent data
attributes). A simplified schema of the ontology is depicted in Figure 20.

Figure 20: Simplified schema of the CREDO Ontology. Classes appear as ovals,
data types appear as boxes. Properties of classes appear as solid arrows,
while the subclass relation appears as dashed arrows with triangular heads.
For legibility reasons the prefix credo: is omitted from classes and property
names.

One part of the classes provides schema for the raw detection data that is
produced by the CREDO Detector app and other sources and is currently
available at the CREDO servers. Instances of the credo:Detection class capture
data associated with each detection. Some of these are directly expressed
using data properties, however the data about the user, their device, the
image captured and the location of the detection are associated as instances
of the respective class credo:User, credo:Device, credo:Location, and
credo:Image.

In addition, the ontology features classes that do not directly correspond to
raw data recorded during detections, but rather they are intended to capture
information derived from the analysis of these data. This includes the class
credo:Shape and its four (mutually disjoint) subclasses credo:Dot, credo:Line,
credo:Worm, and credo:OtherShape. These are used to classify the artefacts
found in the detection images based on their geometric shape analysis.

Finally, if scientific analysis of the detected artefacts, their time frames
and shapes identify that they signify a manifestation of a physical
phenomenon, such phenomena can be captured under the credo:Phenomenon class
and its subclasses, for example credo:Particle, credo:AirShower,
credo:TemporalCluster, and others.

While the CREDO data is currently available in a non-semantic format via the
CREDO API as described above, the full utility of the CREDO ontology will be
reached once the data is also available in the semantic format via a SPARQL
endpoint. This is part of our ongoing efforts.

##  7 Building the scale: public engagement as a scientific need

As explained in more details in Ref. Homola and et al. (2020) (CREDO Collab.),
since a planetary scale and massive, geographically spread data acquisition
with even small detectors such as smartphones are essential for the CREDO
mission, the CREDO Collaboration considers an active engagement in the project
of non-expert science enthusiasts as a methodological must: beneficial both
for the project and for the contributors, and making science experts and non-
professionals just one community, working hand-in-hand towards common goals.
The unprecedented cosmic-ray data set to be collected and processed by CREDO
will require a continuous overlook and vigilance of many people. Thus public
engagement must be planned on many levels: from passive data taking with
smartphones, through simple data monitoring, mining and analysis via the
Internet, to more advanced activities. In practice, it means that CREDO will
offer long-lasting educational and developmental paths for individuals who
became amazed after their first, very close and active contact with science,
and who will be ready for more. If the scale of the CREDO network is as large
as planned, our format must bring benefits not only to the whole science
community but also to the society. Universally useful educational and mind
formation opportunities together with the availability of indirect and
immediate participation in a top-science project for the so-far-excluded
countries, regions and individuals, should contribute to the overall,
sustainable civilizational development of society.

One of the basic (very simple) trigger concepts related to CRE and public
engagement potential concerns global cosmic ray patterns, is illustrated in
Fig. 10, using an example toy CRE simulation (arbitrarily dense and wide
particle front arriving to the Earth from geographical North) and some random
noise. The simulations are thrown on top of a global network of cosmic-ray
detectors which, for simplicity, detect all the particles. One sees that a
strong enough CRE signal can give a visible, global pattern built of the
stations that see particles within some predefined time window. The pattern
can be visualized by putting the locations of the active stations on the globe
map and color-coding average arrival times of all particles hitting the
detectors (top panel of Fig. 21). One can also show the arrival time scatter
plot (bottom-left) or/and average arrival times for the stations located
within a certain territory (bottom-right – here within the 10 degree wide
latitudinal belts). A random pattern is expected to give the average values
located, within the uncertainties, in the middle of the considered time
window, while the CRE-like signal should be visible as a departure from the
“randomness line”. So the pattern classification is based on a distinction
between “flat line in the middle of the window” and “deviations from the flat
line in the middle”. This fundamental simplicity is then similar e.g. to the
popular citizen science project designed to search for new planets, Planet
Hunters Fischer et al. (2012), where the light curves of stars are exposed to
a crowd-sourced classification and the users are asked to look for “transits”
visible as periodic reduction of the received star light. This kind of pattern
recognition is of course easily performed with simple algorithms or neural
networks, nevertheless humans are still needed to classify the images “on the
edge” or “super strange” – seen for the first time and thus obviously not
included in the training sets. In Planet Hunters the number of images suitable
for human-based classification is large, and one expects even larger data load
in the CREDO citizen science interfaces dedicated to global patterns: Private
Particle Detective (still in the prototype phase) Dark Universe Welcome Dar ,
both powered by Zooniverse zoo , the platform which also hosts Planet Hunters.
Thus in both cases the involvement of a large number of users is not just a
funny outreach option, it is a must of fundamental importance: there might be
only a few really important observations (the most Earth-like planets in the
case of Planet Hunters or the clearly non-random super-preshowers in the case
of Dark Universe Welcome) and we do not want to miss them. All hands
(smartphones, other detectors) are needed on board.

Figure 21: The concept of the CRE global pattern detection/alerting. See the
text for details. Homola and et al. (2020) (CREDO Collab.)

Apart from the central public engagement effort there is and will be a number
of peripheral and potentially beneficial activities initiated by both
professionals and non-expert participants of the CREDO program. The room for
having and developing one’s own initiatives and ideas that can be potentially
available and useful to the whole CREDO community has already been proven to
serve as an efficient public attractor. Example results of non-expert
peripheral activities related to CREDO include e.g. Windows/Linux applications
using cameras as radiation detectors CRE ; Cre , or a set of Python and SQL
tools for basic data visualization and analysis Win ; PyC  (see an example
screenshot in Fig. 22).

Figure 22: A basic visualization of the geographical locations of CREDO
detections performed by a script developed by one of the non-expert CREDO
participants.

A very promising direction, both in terms of data acquisition and public
engagement, is a detector application that can be run using a web browser
independently of the operating system of the device. The project named “CREDO-
web-detector” is now being developed by the students of Cracow University of
Technology. It is an attempt to recreate the Android version of the CREDO
Detector mobile application in a web browser environment. Web browsers offer a
good opportunity to reach new participants, as their implementations are
present in all popular operating systems. If a web-browser-based detector
application is used in future, CREDO can be universally opened to Microsoft
Windows, Apple IOS or Linux users. The trial version of CREDO-web-detector
application is available in the public CREDO software repository cre .

Another way of public engagement stimulation and improving the user retention
rate that has already been implemented in CREDO is based on introducing
gamification and edutainment components into scientific projects. For example,
smartphone data acquisition and particle identification studies are noticeably
supported by the prototype team competition in particle detection named
Particle Hunter League hun . During the initial phase of operation advertised
mostly among teachers in southern Poland the competition attracted around 2000
pupils from $\sim$100 teams (schools), and it is now being planned to
internationalize the format beginning from the 17 CREDO member countries.

Apart from a set of easy access solutions CREDO offers also higher level
opportunities like virtual summer practices, supervision of bachelor, master
and PhD projects, and also openness of the scientific teams dedicated to
specific tasks reflecting the central CREDO agenda. More advanced CREDO
participants and users oriented mostly on software development can also
benefit from the fact that CREDO operates using open source codes under the
MIT license mit . This kind of openness enables healthy competition among the
teams of software developers in a hackathon-like style, leading hopefully to a
“natural” evolution of the software solutions within the CREDO program,
although to make use of such non-central software activities a regular quality
and functionality assessment will have to be implemented centrally, with
redirecting the most promising developers and their work to the further
stages, with larger scale funding.

The above highlights and examples well illustrate the societal ambition of
CREDO which can directly be inferred from the deep and novel sense of the
scientific research described above, where the active and massive
participation of the public is rather a necessity than an option. Based on how
the first CREDO users reacted to our concept, and how hungry they were to
participate in a deeply important scientific project as meaningful members –
we are ambitious to ignite a new era in science based on a deep public
engagement in conducting a scientific research, by using smartphones in the
quest for understanding the Universe to the deepest, fundamental level, hence
bringing the worlds of science professionals and “just” enthusiasts closer to
each other than ever.

##  8 Outlook

Figure 23: The CREDO potential contributions to the Time Domain Astronomy
Coordination Hub (TACH), a new NASA initiative. The CREDO logo has been
positioned in two distinct places on top of the slide by Judith Racusin, NASA,
from her invited talk mul  at the New Era of Multi-Messenger Astrophysics
Conference, Groningen, March 2019.

The current status of the Cosmic Ray Extremely Distributed Observatory
described above as well as the dynamics of the progress being made by the
CREDO Collaboration allows an optimistic outlook regarding the future
perspective of further development and the resulting accomplishment of the
ambitious scientific objectives. However, the apparently bright and
scientifically exciting future of the CREDO mission still requires attention
and care today. Apart from the already functional, fast growing own original
data acquisition system which provides first scientific results the CREDO
concept needs to attract more intensely the wide astroparticle physics
community to make an optimum use of the available infrastructures, data
reservoirs and expertise resources – as must be required by any global
approach to the observation and studies on cosmic ray ensembles. This need
naturally does not imply any reorientation or renaming of the existing
scientific collaborations and programs, it just defines a chance for synergy
leading to new observations in the field of astroparticle physics within an
unprecedentedly wide energy regime, including the highest energies known. One
of the pillars of the awaited success is tightly connected with the principles
of Open Science Woelfle et al. (2011) focused on making scientific research
(including publications, data, physical samples, and software) and its
dissemination accessible to all levels of an inquiring society. One of the
advantages of the Open Science research is a potential contained in the inter-
collaborative effort dedicated to multi-messenger and multi-mission projects,
reflected e.g. in the recent NASA initiative named Time Domain Astronomy
Coordination Hub (TACH) Smale et al. (2020), see Fig. 23. CREDO directly
addresses the TACH perspective, although the possible inter-cooperative
activities might have different faces. One of the example directions that have
been already explored is based on the expectations the gamma rays collected by
CTA might be components of Cosmic-Ray Ensembles that CREDO has argued in the
aforementioned Ref. Almeida Cheminant and et al. (2020) (CREDO Collab.), and
there might me more direct links to the other ESFRI ESF  infrastructures. For
example, the unwanted muon background received by KM3NeT Kou (2017) (or any
other underwater neutrino observatory!) might serve as a signal for the CRE-
oriented strategies, and E-ELT Gilmozzi and Spyromilio (2007) (and other
telescopes as well!) can contribute to CREDO by sharing their unwanted cosmic-
ray “artifacts” recorded with the CCD cameras in the “dark frame” mode or
during regular operation. And these are only selected examples given to
illustrate the “connectivity” of the CRE research. We indicate places where
the planned CREDO multimessenger and multimission contributions can be made on
top of the NASA perspective in Figure 23: 1) high energy cosmic rays and
cosmic-ray ensemble alerts provided by CREDO can naturally contribute to TACH
via the Astrophysical Multimessenger Observatory Network (AMON) amo  dedicated
to high energy astroparticle physics phenomena, and 2) the alerts on transient
anomalies in secondary cosmic-ray radiation detection rate can be sent
directly to the Multimission Transient Database. CREDO will of course benefit
also from receiving alerts from TACH which will expand and enrich the scope of
scientific research opportunities (enabling e.g. also studies on the sub-
threshold level) available to the CREDO participants and users. The planned
connection to AMON, and further to the TACH network, will give an opportunity
to further enhance the credibility of the CREDO data, increase its scientific
potential, and stimulate the CREDO infrastructure development adequately to
the expected scientific and societal interest.

It is worthwhile to stress that the multi-mission CREDO potential might
connect the astronomy and astroparticle physics communities with other fields
and create inter- and transdisciplinary opportunities that might turn out to
be of vital everyday life importance for a large fraction of humanity. We list
here a potential for studying correlations of transient anomalies in detection
rates of low energy secondary cosmic rays with seismic effects. The search for
such correlations will be carried out based on multi-messenger signals
received by global networks of detectors, including cosmic-ray sensitive
devices operated by CREDO. Mass movements inside the Earth that lead to
earthquakes simultaneously cause temporary changes in the gravitational and
geomagnetic field. These changes are propagating at the speed of light and can
therefore perhaps be observed on the surface earlier than earthquakes, for
example by registering changes in the frequency of detection of cosmic
radiation, which is very sensitive to geomagnetic conditions. Confirming of
such correlations would give hope for a warning system, and an effort in this
direction has a motivation described in the literature Morozova et al. (2000);
Foppiano et al. (2008); Romanova et al. (2015); Pıša et al. (2010); He and
Heki (2018), however no infrastructure suitable for global studies has been
available.

Another interesting interdisciplinary line of work with CREDO is Space Weather
(and Space Climate over long periods of time). Besides a lot of possibilities
for specialists, CREDO can be used as an excellent introduction to space
weather for the general public since cosmic rays are a fundamental part of the
space environment. Until now, the classic experiment that served as an
introduction to space weather for the general public was the counting of
sunspots with a modest telescope Muñoz-Jaramillo and Vaquero (2019). However,
the generalization of mobiles makes CREDO an ideal instrument to engage the
general public interested in Space Weather.

Another interdisciplinary opportunity is global monitoring of the locations
and arrival times of extensive air showers. Average doses from cosmic ray
radiation are known to be significantly lower than those due to local and
natural radiation, but it is yet unknown what impact on biological systems
comes from irradiation by very energetic EAS, especially their central
regions. Particle mass composition, density and energy distributions there
contribute to a single radiation dose which is hard or infeasible to mimic in
laboratories, and thus not available for direct reflecting/projecting in basic
laboratory research. The CREDO infrastructure will enable this sort of pioneer
investigation by connecting geographic coordinates and arrival times of
energetic EAS cores with the locations of humans engaged in the project,
providing the data for long-term studies on possible correlations between
cosmic radiation and our health. Such studies will potentially lead to
explaining the causes of some diseases of unknown aetiologies, with hope for
new therapies and/or preventive examination strategies. This interdisciplinary
research will go beyond the existing research frameworks both in the fields of
the physics of cosmic radiation itself and concerning the knowledge about the
possible biological response of the human body to this radiation. Our studies
will be conducted in accordance with the global trends in understanding the
impact of low doses of radiation on living organisms in terms of the
possibility of the occurrence of both positive phenomena (e.g. increasing the
immunity of organisms) and negative ones (e.g. some types of cancer) Kreuzer
et al. (2018). These studies may shed light on interesting facts that still
cannot be explained as the strong inverse correlation found in Italy between
high solar activity and incidence of schizophrenia and bipolar disorder
Ventriglio et al. (2011).

##  9 Summary and Conclusions

With CREDO we are going to explore a new observation channel of the Universe,
the CRE channel. The width and complexity of the scope of the studies point to
a long-term research perspective, and to the need of engaging wide communities
of both professional scientists and non–expert science enthusiasts. The
outcome of this program will tell whether the CRE channel broadcasts with New
Physics or “just” new upper limits to astrophysical and cosmological scenarios
based on null CRE results. If CRE are observed, they could point us back to
the interactions at energies close to the GUT scale and lead us to a
breakthrough in physics. If CRE are not observed, we will set the new upper
limits constraining selected theories, e.g. the SHDM models, which will point
to a new way to narrow the search for a breakthrough in science. You are
welcome to join us!

conceptualization, P.H., T.W.; methodology, D.Be., N.D., P.G., K.G., M.H.,
P.H., M.Kar., R.K., S.K., M.M., J.W.M., A.N., M.N., C.O., K.O., M.Pa., K.Sme.,
O.S., T.W.; software, Ł.Bi., M.B., D.Bu., A.Ć., N.D., A.R.D., P.G., M.Kn.,
S.K., M.M., J.Mę., M.N., K.O., M.Pa., M.Pi., B.P., S.S., O.S.; validation,
M.B., P.H., J.Mę., B.P., S.S., O.S.; formal analysis, J.P., W.S., T.W.,
K.W.W.; investigation, M.B., K.A.C., N.D., P.H., J.Mę., B.P., J.P., W.S.,
S.S., O.S., T.W., K.W.W.; resources, P.H., M.Kn., M.M., M.N., B.O., K.O.,
M.Pa., M.R., J.Su.; data curation, N.D., M.H., Z.H., O.S., S.S.; data science,
Ł.Bi., M.Pi., K.Rz.; theoretical studies, Ł.Br., D.E.A.C., N.D., D.G., J.J.,
M.V.M., Y.J.N, J.Z.-S., A.T.; writing–original draft preparation, D.Be.,
Ł.Br., D.E.A.C., K.A.C., N.D., P.G., K.G., D.G., A.C.G., J.J., S.K., M.H.,
P.H., R.K., M.Kn., M.V.M., J.W.M., A.N., C.O., K.O., M.Pa., J.P., K.R.,
J.Z.-S., K.Sme., W.S., S.S., O.S., A.T., T.W., K.W.W.; writing–review and
editing, D.Be., G.B., Ł.Br., N.B., K.A.C., D.E.A.C., P.D., A.R.D., K.G.,
A.C.G., M.H., P.H., M.Kas., R.K., P.K., B.Ł., A.M., M.V.M., J.Mi., V.N.,
Y.J.N, B.O., G.O., M.Pa., M.R., K.R., J.Z.-S., K.Sme., K.Smo., J.St., S.S.,
O.S., M.S., A.T., K.T., J.M.V., T.W.; visualization, M.Kn., S.S., Z.H.;
supervision, Ł.Bi., A.R.D., P.H., D.G., R.K., J.W.M., M.R., K.R., S.S., J.Su.,
T.W., K.W.W.; project administration, P.H., R.K., M.M., S.S.; funding
acquisition, M.H., R.K., A.T.

This research was partly funded by the International Visegrad grant No.
21920298. N. Budnev acknowledges partial support from The Russian Federation
Ministry of Education and Science (Tunka shared core facilities – unique
identifier RFMEFI59317X0005), J. Zamora-Saa acknowledges support by FONDECYT
(Chile), grant No. 3180032, M.V. Medvedev acknowledges partial support via the
NSF grant No. PHY-2010109, the DOE EPSCOR grant No. DE-SC0019474 and the DOE
grant No. DE-SC0016368, and Martin Homola is supported by Slovak VEGA grant
No. 1/0778/18. J.M. Vaquero acknowledges support from Junta de Extremadura-
Fondo Social Europeo (GR18097).

###### Acknowledgements.

We acknowledge the leading role in the CREDO Collaboration and the commitments
to this research made by the Institute of Nuclear Physics Polish Academy of
Science. This research has been supported in part by PLGrid Infrastructure and
we warmly thank the staff at ACC Cyfronet AGH-UST for their always helpful
supercomputing support. We thank Steven Carlip, Roger Clay, Bohdan Hnatyk,
Qingdi Wang, and Henryk Wilczyński for valuable remarks and discussions. The
authors declare no conflict of interest. The following abbreviations are
frequently used in this manuscript:
CR | Cosmic Ray(s)
---|---
CRE | Cosmic Ray Ensemble(s)
CREDO | Cosmic Ray Extremely Distributed Observatory
EAS | Extensive Air Shower(s)
UHECR | Ultra-High Energy Cosmic Rays
References yes

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