Improvements in the on-orbit calibration of the Terra MODIS short-wave infrared spectral bands

Abstract

The short-wave infrared (SWIR) bands (5-7, 26) of Terra MODIS, co-located with the mid-wave infrared (MWIR) bands (20-25) on the short and mid-wave infrared (SMIR) Focal Plane Assembly (FPA) have a known issue related to 5.3 μm out-of-band (OOB) thermal leak and electronic crosstalk that was identified prelaunch. Intensive efforts were undertaken shortly after launch to mitigate its impacts on the on-orbit calibration and in turn the level 1B (L1B) products. In order to the isolate the OOB contribution among the SWIR bands, special night time day mode (NTDM) operations have been regularly scheduled to collect Earth scene reflective solar bands (RSB) data during spacecraft night time. As MODIS does not have a spectral band centered at 5.3 μm, measurements from the MODIS Airborne Simulator (MAS) spectrometer field campaigns in the early months after Terra launch were used to help identify band 28 (7.325 μm) as the best surrogate to simulate the radiances at 5.3 μm. As a result, band 28 is used as the sending band for the SWIR crosstalk correction for Terra MODIS. In the case of Aqua MODIS, band 25 (4.52 μm) was found to be more effective as the sending band for the SWIR crosstalk correction. In recent years, the Terra MODIS PV LWIR electronic crosstalk (including band 28), has gradually increased, more significantly after the safe-mode event occurred in Feb, 2016. This accentuated degradation in the PV LWIR performance has also impacted the performance of on-orbit SWIR crosstalk correction algorithm and thus the L1B products. In this paper, we examine the use of band 25 as the sending band for Terra MODIS SWIR crosstalk correction and compare its performance with that based on band 28 as the sending band. Results indicate an improvement in the stability of the on-orbit gain for the SWIR bands and a reduced detector-detector and subframe striping in the L1B products, especially during the period when the PV LWIR electronic crosstalk is more severe.