Case #:PM_NPP_L1B_20017  Opening date: 01/17/20  Last update: 01/21/20 |
There has been an anomaly in the VIIRS SDR reflective bands calibration for both NOAA-20 and S-NPP because of incorrect solar vector calculations since about 2020-01-16 0:00 UTC. NOAA has stated that for S-NPP VIIRS SDR, both radiance and reflectance products are affected because the RSB calibration coefficients have not been updated since 2020-01-16 0:00 UTC. For NOAA-20 VIIRS SDR, radiance products should not be affected by this anomaly, but the reflectance products are affected because of the solar zenith angle errors.
However, any direct impact of this on the NASA LandSIPS L1B calibration will be minimal as the calibration of L1B radiance products in LandSIPS is not dependent on the solar vector. The impact on the L1B reflectance products should also be small of around 0.1%, mainly coming from errors in the Earth-Sun distance. The NASA LandSIPS downstream land products will be impacted however, through any impact on the cloud mask and from inaccurate day/night delineation and compositing of values in L3 downstream products, based on the high sun angle. This issue will also directly impact the active fire products, where false fires have been observed.
***** NOTE 01.21.20 *****
A corrected LUT, containing the fix for the planetary ephemeris LUT, was delivered by VCST and was put in place for NRT processing from 01/18/2020 processing from:
2020.017.2218 - AS 5001 - S-NPP
2020.017.2218 - AS 5000 - S-NPP
2020.018.1236 - AS 5200 J1/N20.
All L1/L2 and downstream products are now considered to be nominal.
LandSIPS Forward Processing:
Additionally, the corrected LUT containing the fix for the planetary ephemeris LUT, was put in place for Land SIPS Forward Processing from 01/17/2020 (S-NPP; AS 5000/AS 5110) and from 01/18/2020 (J1; AS 5200). The exact timings, when the corrected L1B LUT was put into place are
J1 AS 5200: 2020.018.0948
S-NPP AS 5110: 2020.017.1112
S-NPP AS 5000: 2020.017.1000.
Hence, all data from forward processing will be nominal from day 01/18/2020 for C1 S-NPP (AS 5000, AS 5110) and from day 01/19/2020 for C2 J1 (AS 5200). This note will be updated when the reprocessing has occurred.
The global browse example images below from the Near Real Time processing stream show the initial downstream impacts to the L2 Surface Reflectance product, Snow product, and Ice Surface Temperature that are expected during this calibration anomaly period. In the examples below DOY 2020.015 is shown on the left for comparison prior to the calibration anomaly. The images on the right, show how the downstream products are impacted, specifically effect on day/night delineation in the high latitudes.
Occurrence: All products S-NPP and N20 archives during the specified time period.
PGE: Land SIPS