An update to the calibration algorithm of the MODIS PV LWIR bands for Collection 7 to improve long-term records

MODIS Collection 6.1 (C6.1) is the current official version of its NASA Level-1B (L1B) product, while the Collection (C7) production is presently underway. Amongst the various improvements from its preceding Collections, the most impactful development in C6.1 was the application of a correction to reduce the crosstalk contamination between the MODIS photovoltaic longwave infrared (PV LWIR) bands. In the case of Terra MODIS, such correction was applied via reprocessing to the long-term record, whereas for Aqua MODIS, it was implemented starting March 2022 after the spacecraft and MODIS entered into a safe mode state that significantly increased the crosstalk contamination between the instrument’s PV LWIR bands. In MODIS C7, such correction is applied from mission beginning. Over recent years, both MODIS sensors have seen a gradual crosstalk increase, this in turn has caused drifts across different Earth view scenes despite the correction application, since it can’t completely remove the crosstalk contamination. These drifts are most critical for Aqua band 29 (vastly used by the science community) and Terra band 30. In the case of Aqua MODIS band 29, this is true for both C6.1 and C7, whereas for Terra MODIS band 30, the downward trend is most significant in C6.1 and overcorrected in C7. This led the MODIS Characterization Support Team (MCST) to assess and develop a strategy to reduce these drifts in C7. The methodology involves updating the algorithm used to generate the on-orbit derived calibration coefficients and scaling the crosstalk correction coefficients. However, after several discussions with science teams whose higher-level products ingest the MODIS Level-1B products, the latter was dispensed. The original and revised strategies are discussed. Overall, the agreed upon approach successfully reduces the long-term drifts for all the MODIS PV LWIR bands whose algorithm was updated. Close to pushing the quarter century mark, the Terra and Aqua MODIS legacy instruments will be essential to perpetuate long-term environmental data records after these are superseded by more novel sensors such as VIIRS. Hence the need for the algorithm updates presented in this work to maintain stable data archives.