Performance of the Semi-Empirical Precipitable Water Vapor Retrieval Algorithm Developed for Polarized Scanning Atmospheric Corrector (PSAC) in the Presence of Sensor Decay

Polarized scanning atmospheric corrector (PSAC) is an optical sensor onboard HuanjingJianzai-2 (HJ-2) A/B satellite. One of its missions is to monitor precipitable water vapor (PWV) by using its near-infrared (NIR) channels. Since the accuracy of the commonly used NIR PWV retrieval algorithm developed based on the radiative transfer model (RTM) would be significantly affected by the radiometric decay of sensors, and the recalibration of decayed sensors is a complex process, it is interesting and necessary to find a robust PWV retrieval algorithm that is not affected by sensor decay. At present, a semi-empirical algorithm constructed based on the matching results between ground-based PWV data and the actual PSAC observations has been used for the PWV retrieval of PSAC. Since the systematic calibration error of PSAC is considered in constructing the algorithm, it should be able to remove the negative effects of sensor decay on PWV retrieval results. Because the above inference has not been confirmed quantitatively, it is necessary to evaluate the accuracy of the algorithm in the presence of sensor decay. The evaluation results based on simulated data show that the accuracy of the semi-empirical algorithm does not change regardless of the presence or absence of radiometric decay in PSAC. Moreover, the algorithm is used for PWV retrieval of MODIS to test its effectiveness. Compared with the official PWV data developed based on RTM, the MODIS PWV data developed by using the semi-empirical algorithm are reduced by more than 50% in both absolute and relative errors (REs).