On gain transition discontinuity in VIIRS on-orbit calibration

The VIIRS instrument captures reflected solar or emitted thermal radiation from the Earth in selected wavelengths. Each wavelength is covered by a band of detectors. Some bands are dual gain and conduct measurements in a more sensitive high gain (HG) stage for enhanced resolution in the lower radiance range, and transit to a low gain (LG) stage for the higher radiance. A slight discontinuity in the derived radiance can be observed around the gain transition, with calibrated radiance values that appear either missing or duplicated in both gains. This paper illustrates that the gain transition discontinuity (GTD) is a side effect of the on-orbit calibration method, and shows a possible way to adjust the calibration coefficients to make the LG and the HG results more consistent under certain conditions. The nonlinear behaviors of the calibrated results around the GTD that are not captured during the pre-launch test are also revealed. Because of the complexity and uncertainty in the on-orbit calibrations, we recommend to improve the pre-launch test to characterize the GTD in advance.