JPSS-2 VIIRS Prelaunch Geometric Performance and Characterization

The NASA/NOAA Visible Infrared Imaging Radiometer Suite (VIIRS) is a key instrument in the JPSS missions (SNPP, JPSS-1-4). VIIRS data will be used by the science research community to continue long-term measurements of geophysical variables and by the operational community for weather forecasting and disaster relief and other applications. Being part of the calibration and validation process, JPSS-2 VIIRS prelaunch geometric performance assessment focuses on the sensor’s spatial response, band-to-band co-registration, and geolocation accuracy. In general, JPSS-2 VIIRS’ prelaunch geometric performance is very good, and consistent with SNPP and JPSS-1 VIIRS. This paper highlights some specific key findings from the JPSS-2 VIIRS’ prelaunch tests. We first show motor axis rework reduced JPSS-2 VIIRS half-angle mirror (HAM) side difference from 10% (about 20 arcsec) mis-registration of an M-band sample to 0.01% at both 0- and 23-degree tested scan angles. Another finding from the prelaunch test is that JPSS-2 VIIRS has relatively larger band-to-band co-registration errors between VisNIR and LWIR bands in the scan direction, which was corrected using timing adjustments. In the end, we discuss the unsymmetrical Day Night Band (DNB) scandirection Line Spread Function (LSF) of JPSS-2 VIIRS at different gain stages and aggregation modes. The magnitude of the side lobe at one sample is closely correlated with illumination strength, specifically the form of a logarithmic function of the maximum raw sensor output in digital number (DN). As a result, this unsymmetrical LSF will affect the radiometric outputs in the neighboring pixels. We generate simulated JPSS2 VIIRS DNB images using SNPP image and a logarithm fitted model, which help the science community to evaluate how this side lobe effect may impact their applications