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Thermal Leak (Bands 5, 6 ,7 and 26)

Description

Thermal out-of-band leakage into the SWIR Bands (5, 6,7,and 26) was evaluated by viewing the Earth at night with the MODIS instrument in day mode. Band 28 was selected to determine the leak coefficients. These coefficients were applied to mitigate the effect. The coefficients have been applied to the calculation of m1 after 12/16/2002, LUT version 4.1.1.1. Energy near 5.3 µm contributes to the SWIR bands (Bands 5, 6, 7 and 26). In June 2003, Band 25 was selected to determine the leak coefficients. These coefficients have been applied to the calculation of m1 after this period using LUT version 4.1.5.1 and higher.

Impact to L1B Data Set

Affects the calibration accuracy due to the scene dependence of the thermal leak.

Estimated Impact to L2 Science Products

Affects the calibration accuracy due to the scene dependence of the thermal leak.

Cause of Effect

The spectral out-of-band blocking filters were not designed to cover the complete long-wavelength sensitivity for the SW/MWIR focal plane. The consequence for MODIS Terra is that the SWIR bands are sensitive to thermal signals extending out to near 5.3 µm. Calibration had been performed with the Solar Diffuser using a constant scene brightness.

Mitigation Approach/ Added Testing to Characterize Effect

The correction for this effect is based on the use of measurements for MODIS in Band 28, because the spectral weighting function of that band is closest in most geophysical conditions to the contributions from energy near 5.3 µm. The use of Band 28 as a proxy for 5.3 µm energy breaks down in the presence of very low atmospheric precipitable water (where the Band 28 signal receives energy directly from the surface). When this condition occurs over a hot surface (desert) the present algorithm provides too large a correction. When this condition occurs over a cold surface (arctic fields) the correction remains good.

Estimated Schedule to Complete

Completed. The correction was turned "on" again with the September 2001 LUT delivery version 3.0.0.6. This LUT will be applied to the new side A data acquired from July 2, 2001 and beyond.