Estimation of Total Atmospheric Water Vapor Content Using MODIS Channels 31 and 32

摘要

A new approach for retrieval of the total atmospheric water vapor content (TAWV) based on the Moderate Resolution Imaging Spectrometer (MODIS) two thermal IR (TIR) channels (ch31 and ch32) is proposed. To developing the approach, the radiative transfer calculations are carried out using MODTRAN 4.0 combined with the latest global assimilated data, and the pixels contaminated by clouds are eliminated using cloud detection techniques. Total 6757 sets of atmospheric profiles are carefully selected. The relationship between the transmittance ratio at the two TIR channels and water vapor content is set up, with a third order polynomial of the transmittance ratio. Meanwhile, the split-window covariance-variance ratio (SWCVR) method is reviewed and the error caused by the assumptions for the method is analyzed. The new approach is tested with the MODIS data in North China region, and compared with the radiosonde data and MODIS official water vapor products. Compared the TAWV results estimated by our approach with the radiosonde data, the root-mean-square error (RMSE) is 0.39 g/cm~2. So the proposed approach is able to provide an estimation of the TAWV.