provides an overview of preflight ground testing and instrument characterization, as well as inflight calibration routines. Section \[sec:merging\] presents the algorithm used to combine the FIELDS magnetometer data into a merged product with optimal signal to noise characteristics. Section \[sec:inflight\] provides a summary of our in-flight verification of the calibration and a quantitative analysis of the performance of the merged survey data, and discusses merging survey rate data with DFB burst data [@Malaspina2016].

FIELDS Calibration {#sec:cal}
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Fluxgate Magnetometers (MAG)
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The two fluxgate magnetometers, designed and fabricated at NASA/GSFC, measure DC and low frequency fluctuating magnetic fields. They are placed 1.9 and 2.7 meters from the spacecraft and are respectively referred to as the inboard (MAGi) and outboard (MAGo) sensors. The heritage of the PSP/FIELDS MAGs dates to the 1960’s NASA [*[Explorer 33]{}*]{} mission [@Ness1971; @Acuna1974; @Acuna2002]. Many iterations of the instrument currently operate on both NASA heliophysics and planetary science missions [@Lepping1995; @Acuna2002; @Acuna2008; @Kletzing2013; @Connerney2015; @Connerney2017]. The PSP fluxgate magnetometers have a maximum survey mode sample rate of $f_{svy}^{max}=292.969$ Sa/s. The MAG data is typically downsampled by factors of two with anti-aliasing performed with a Bartlett filter. Generally, MAGi is run at a lower sample rate in 