Tracking long-term stability of the response versus angle for the MODIS thermal emissive bands with observations over clear ocean

Abstract

This study uses observed brightness temperatures (BT) over clean ocean to track the stability of the onorbit response versus scan angle (RVS) for the thermal emissive bands (TEB) of the MODIS (the Moderate Resolution Imaging Spectroradiometer) instrument onboard Aqua and Terra spacecraft. The stability is examined by tracking the BT difference between those obtained at each scan angle and the scan angle of the view for the onboard blackbody. Over two thousands granules over the Atlantic Ocean for Terra and Aqua MODIS are used. Cloudy pixels within each granule are excluded to improve trending quality and consistency. The BT trends are derived at 13 angles of incidence (AOI) over the entire Aqua and Terra missions. Results show that the relative changes in BT for the long-wave infrared bands are within a few tenths of a degree, equivalent to 0.5 to 1.0%, while those for a few middle-wave infrared bands still show large fluctuations due to their high sensitivity to atmospheric water vapor contents. A comparison with trends obtained using measured BT for instrument interior cavity shows that both results are in good agreement. The BT differences between two mirror sides at each scan angle are also derived to examine the consistency of the RVS results.