JPSS-4 VIIRS prelaunch geometric calibration and characterization status

The NASA/NOAA Visible Infrared Imaging Radiometer Suite (VIIRS) is a key instrument in the JPSS missions (SNPP, JPSS-1-4). Being part of the calibration and validation process, JPSS-4 VIIRS prelaunch geometric performance assessment focuses on the sensor’s spatial response, band-to-band co-registration (BBR), and pointing knowledge. In general, JPSS-4 VIIRS’ prelaunch geometric performance is very good, and consistent with SNPP and JPSS-1-2-3 VIIRS. This paper highlights some specific key findings from the JPSS-4 VIIRS’ prelaunch tests. We first show that with timing adjustments, JPSS-4 VIIRS scan BBR error between VisNIR and SMWIR and LWIR bands has been reduced from 0.11/0.04 M-band sampling intervals to around 0.01 M-band sampling intervals, respectively. Focal Plane Assembly (FPA) rotations are about 0.03 degree in VisVIR, 0.08 degree in SMWIR and LWIR. Another finding from the prelaunch test is that JPSS-4 VIIRS track direction band-to-band co-registration errors between VisNIR and SMWIR and LWIR bands have been improved when compared to JPSS-3. This BBR mis-registration increases when aft‐optics assembly (AOA) temperature decreases. During TVAC cold performance test (AOA temperature is 253K), the track BBR mis-registration is about 0.04 M-band sampling intervals between VisNIR and SMWIR bands, and 0.03 M-band sampling intervals between VisNIR and LWIR bands. By comparison, the track BBR mis-registration in JPSS-3 is 0.10/0.08 M sampling intervals between VisNIR and SMWIR/LWIR bands, respectively. The unsymmetrical Day Night Band (DNB) scan-direction Line Spread Function (LSF) of JPSS-2 VIIRS at different gain stages and aggregation modes have been corrected in J4 VIIRS. Lastly, to correct the scan-to-scan underlaps in J1/J2, the scan rate of J4 VIIRS is increased to 3.546 rad/sec, compared to 3.510 rad/sec of J2. As a result, NOAA IDPS will reduce from 85.35 sec to 85.00 secs in each 48-scan granule, and NASA LSIPS will increase the number of scans from 202 scans in J2 to 204 scans in J4 in each 6-minute granule.