Abstract
The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the National Oceanic and Atmospheric Administration - 21 (NOAA-21) satellite was successfully launched on November 10, 2022. NOAA-21 VIIRS Cold Focal Plane Assembly (CFPA) temperature reached 82 K on February 10, 2023, and the Thermal Emissive Band (TEB) Sensor Data Record (SDR) products became available. This study presents NOAA-21 VIIRS TEB on-orbit performance.
Differently from the VIIRS onboard S-NPP and NOAA-20 satellites, NOAA-21 VIIRS TEBs have experienced three phases of on-orbit responsivity changes during its early mission. The first phase is from launch to March 3, 2023. Small degradation in the TEB detector responsivities was observed during early February 2023, with the long-wave infrared (LWIR) bands exhibiting relatively larger degradation. A mid-mission out-gassing (here referred to as MMOG-1) was performed on February 23, 2023, to remove potential water ice contamination. After the MMOG-1, TEB gains returned to the levels similar to the beginning of the mission.
The second phase is from March 3 to March 9, 2023. NOAA-21 VIIRS CFPA setpoint temperatures were lowered from 82 K to 80 K on March 3, 2023, to further enhance the TEB noise performance. LWIR NEdTs were significantly reduced. In addition, LWIR gains jumped after the switch, with M14 showing the largest increase (~11%). After this event, NOAA-21 VIIRS TEB gains had remained stable until mid-March, 2023.
The third phase of gain change is the newly occurred degradation since mid-March 2023, started approximately at the same time as the much rapid degradation observed in the NOAA-21 shortwave infrared (SWIR) gains. Different from the pre-MMOG-1 degradation, mid-wave infrared (MWIR) bands degraded much faster than the LWIR ones. By February 2024, MWIR degradation was up to ~6%. Moreover, the MWIR degradation is detector dependent (up to ~10% for some M12 and I4 detectors). The impacts on noise and saturation radiance become more obvious over time for the detectors with larger degradation. During this phase, the degradation of LWIR is much smaller compared to MWIR, but still at least 2 times as fast as that for NOAA-20 LWIR after the respective MMOG in 2018. A second NOAA-21 VIIRS MMOG (referred to as MMOG-2) was performed on February 26-29, 2024. Preliminary assessment results suggest that the MMOG-2 is successful, with TEB gains mostly reversed to the March 4, 2023 levels. Comprehensive results will be given after more data are available. Moreover, the calibration stability and biases in the NOAA-21 VIIRS TEB SDRs since the beginning of the mission will also be presented to benefit downstream applications.
NOAA-21 VIIRS Thermal Emissive Band (TEB) On-Orbit Performance
The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the National Oceanic and Atmospheric Administration - 21 (NOAA-21) satellite was successfully launched on November 10, 2022. NOAA-21 VIIRS Cold Focal Plane Assembly (CFPA) temperature reached 82 K on February 10, 2023, and the Thermal Emissive Band (TEB) Sensor Data Record (SDR) products became available. This study presents NOAA-21 VIIRS TEB on-orbit performance.
Differently from the VIIRS onboard S-NPP and NOAA-20 satellites, NOAA-21 VIIRS TEBs have experienced three phases of on-orbit responsivity changes during its early mission. The first phase is from launch to March 3, 2023. Small degradation in the TEB detector responsivities was observed during early February 2023, with the long-wave infrared (LWIR) bands exhibiting relatively larger degradation. A mid-mission out-gassing (here referred to as MMOG-1) was performed on February 23, 2023, to remove potential water ice contamination. After the MMOG-1, TEB gains returned to the levels similar to the beginning of the mission.
The second phase is from March 3 to March 9, 2023. NOAA-21 VIIRS CFPA setpoint temperatures were lowered from 82 K to 80 K on March 3, 2023, to further enhance the TEB noise performance. LWIR NEdTs were significantly reduced. In addition, LWIR gains jumped after the switch, with M14 showing the largest increase (~11%). After this event, NOAA-21 VIIRS TEB gains had remained stable until mid-March, 2023.
The third phase of gain change is the newly occurred degradation since mid-March 2023, started approximately at the same time as the much rapid degradation observed in the NOAA-21 shortwave infrared (SWIR) gains. Different from the pre-MMOG-1 degradation, mid-wave infrared (MWIR) bands degraded much faster than the LWIR ones. By February 2024, MWIR degradation was up to ~6%. Moreover, the MWIR degradation is detector dependent (up to ~10% for some M12 and I4 detectors). The impacts on noise and saturation radiance become more obvious over time for the detectors with larger degradation. During this phase, the degradation of LWIR is much smaller compared to MWIR, but still at least 2 times as fast as that for NOAA-20 LWIR after the respective MMOG in 2018. A second NOAA-21 VIIRS MMOG (referred to as MMOG-2) was performed on February 26-29, 2024. Preliminary assessment results suggest that the MMOG-2 is successful, with TEB gains mostly reversed to the March 4, 2023 levels. Comprehensive results will be given after more data are available. Moreover, the calibration stability and biases in the NOAA-21 VIIRS TEB SDRs since the beginning of the mission will also be presented to benefit downstream applications.