On-orbit polarization channels registration of multi-angle polarization imager under satellite backward flight

The polarization payload onboard Fengyun-3 precipitation satellite (FY-3G) is the first Polarization and Multi-Angle Imager (PMAI) with a shortwave infrared channel in China. Three spectral bands are equipped with polarizers : 1030 nm, 1370 nm and 1640 nm. For each of these wavelengths, three similar spectral filters are associated with three polarizers, the direction of the first and the third one being at +60° and -60° from the direction of the central one. The three polarization image of the band are obtained from the subsequent detector response. To compensate for the flight lag, the design uses the wedge prism to register the three images together. The satellite adopts an autonomous 180° yaw maneuver control scheme to guarantee the on-orbital performance. In order to solve the problem of polarization channel registration of imager during satellite inverted flight, we developed a set of on-orbit registration algorithms. In order to verify the effect of the registration algorithm during the inverted flight, we used a typical observation scence to perform pre- and post-calibration tests. During the forward flight of the satellite, the cloudbow from polarization channel was obtained by PMAI. However, during the backward flight due to the wrong channel registration between sub-pixels, the rainbow is drowned in noise. After calibrated by the on-orbit registration algorithms in backward flight, the cloudbow come to appear in the 140° scattering angle. Results show that during inverted flight the registration effect is greatly improved, and the accuracy of polarization observation is dramatically enhanced.