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Satellite multi-detector cross-track scanners, such as MODIS (Moderate Resolution Imaging Spectroradiometer) and
VIIRS (Visible-Infrared Imaging Radiometer Suite), require synchronization of optical and orbital characteristics to avoid
gaps in Earth coverage between scans. Prelaunch tests have revealed that such scan-to-scan gaps will occur near nadir in
VIIRS observations from the future JPSS-1 (Joint Polar Satellite System) and JPSS-2 satellites. Our analysis of VIIRS
geolocation products shows that the gaps do not occur for the instrument currently on orbit onboard the S-NPP (Suomi
National Polar-orbiting Partnership) spacecraft. When the same analysis is applied to the MODIS data products, it reveals
that small, near-nadir gaps exist in MODIS observations from both Aqua and Terra satellites. Although magnitude of the
MODIS scan overlap gaps (up to 100 m for Terra and 25/175 m for Aqua) is quite small in comparison to the 1-km pixels,
it is rather significant for the bands with the 250-m and 500-m pixels. Despite the size of the gaps, it appears that their
effects on scientific analyses (e.g., NDVI) have not been reported since launch of the MODIS instruments. Because the
gaps currently predicted for the JPSS-1 and -2 VIIRS are similar in size to the ones occurring for MODIS, one can expect
that their effects on science data will be similarly negligible. A model that uses S-NPP orbit data as well as the S-NPP
VIIRS telescope’s focal length and scan rate predicts the overlap that agrees very well with the analysis of the geolocation
data. For JPSS-1/-2 VIIRS focal length and scan rate, the model predicts scan overlap gaps of more than 100 m. With a
shorter focal length and a faster scan rate than for the JPSS-1/-2 VIIRS, the scan overlap gaps are expected to be avoided
altogether for VIIRS on the future JPSS-3 and -4 satellites.
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