A MODIS Dual Spectral Rain Algorithm

Abstract

The Moderate Resolution Imaging Spectroradiometer (MODIS) dual spectral rain algorithm (MODRA) is developed for rain retrievals over the northern midlatitudes. The reflectance of the MODIS water vapor absorption channel at 1.38 ?m (R1.38 ?m) has a potential to represent the cloud-top height displayed by the brightness temperature (TB) of the MODIS channel at 11 ?m, because of an excellent negative relationship (correlation coefficient ≤?0.9) between R1.38 ?m and TB11 ?m for optically thick clouds with reflectance (R0.65 ?m) greater than 0.75. With a training rainfall dataset from the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) aboard the same Aqua satellite platform, two MODIS channels (R1.38 ?m and R0.65 ?m) are applied to form multiregression curves to estimate daytime rainfall. Results demonstrate that the instantaneous rain rates from MODRA, independent AMSR-E rainfall products, and surface rain gauge measurements are consistent. This study explores a new way to estimate rainfall from MODIS water vapor and cloud channels. The resulting technique could be applied to other similar satellite instruments for rain retrievals.