Abstract
The NOAA-20 spacecraft (formerly JPSS-1) executed a series of yaw maneuvers on January 25 and 26, 2018 designed to validate / characterize the transmittance functions of the Visible Infrared Imager Radiometer Suite (VIIRS) instrument solar diffuser (SD) and solar diffuser stability monitor (SDSM) views. On orbit, only the product of the attenuation screen transmittance and SD bidirectional reflectance distribution function (BRDF) can be measured for the VIIRS detector and SDSM SD views. For the SDSM solar view, the attenuation screen transmittance was directly measured. All three transmittance functions were compared to the at-launch functions derived from pre-launch characterization and their effect on the instrument responsivity estimation and SD degradation trending on-orbit was investigated. While both the SD views showed good agreement with the at-launch values (within 0.1 – 0.2 % averaged over a given orbit), the differences in the SDSM solar screen vignetting function relative to the pre-launch estimate impacted the SD degradation by ±1 %. Although the vignetting function derived from the yaw maneuvers considerably improved the SD degradation trending, significant oscillations in the trending remained. The angular sampling provided by the yaw maneuver data was too coarse to capture the fine structure of the vignetting function; additional maneuvers may be added to improve the fidelity of the function. An uncertainty analysis was also conducted on all transmission functions derived.
Yaw Maneuver Analysis for JPSS-1 (NOAA-20) VIIRS
The NOAA-20 spacecraft (formerly JPSS-1) executed a series of yaw maneuvers on January 25 and 26, 2018 designed to validate / characterize the transmittance functions of the Visible Infrared Imager Radiometer Suite (VIIRS) instrument solar diffuser (SD) and solar diffuser stability monitor (SDSM) views. On orbit, only the product of the attenuation screen transmittance and SD bidirectional reflectance distribution function (BRDF) can be measured for the VIIRS detector and SDSM SD views. For the SDSM solar view, the attenuation screen transmittance was directly measured. All three transmittance functions were compared to the at-launch functions derived from pre-launch characterization and their effect on the instrument responsivity estimation and SD degradation trending on-orbit was investigated. While both the SD views showed good agreement with the at-launch values (within 0.1 – 0.2 % averaged over a given orbit), the differences in the SDSM solar screen vignetting function relative to the pre-launch estimate impacted the SD degradation by ±1 %. Although the vignetting function derived from the yaw maneuvers considerably improved the SD degradation trending, significant oscillations in the trending remained. The angular sampling provided by the yaw maneuver data was too coarse to capture the fine structure of the vignetting function; additional maneuvers may be added to improve the fidelity of the function. An uncertainty analysis was also conducted on all transmission functions derived.