Toward improved characterization of remotely sensed precipitation regimes with MODIS/AMSR-E blended data techniques

The multispectral sensing capabilities afforded by the 36-channel Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard the Earth Observing System (EOS) Terra and Aqua satellites have the potential to improve satellite-derived cloud and precipitation products. Included in this channel suite are spectral bands having particular sensitivity to both cloud vertical distribution and near cloud-top microphysics. EOS Aqua, the local afternoon crossing satellite, carries in addition to MODIS the Advanced Microwave Scanning Radiometer for EOS (AMSR-E), a conically scanning passive microwave (PMW) instrument with 12 channels between 6.9 and 89 GHz. While limited by revisit time from low-earth orbit, Aqua provides an ideal test bed for investigating high refresh-rate, geostationary-based blended PMW/optical-spectrum techniques related to improved cloud characterization and precipitation. As the need for improved subdaily quantitative precipitation analysis has grown in recent years, blended-satellite techniques have taken on added relevance. In this paper, we present an application of the MODIS/AMSR-E sensor combination related to potential improvements to the Naval Research Laboratory (NRL)-developed blended-satellite precipitation technique, involving the characterization of cirrus clouds. The presence of cirrus clouds above and nearby to both convective and stratiform precipitation imposes a limit to the utilization of longwave (>10 μm wavelength) thermal infrared channels for precipitation techniques. The established "split window" technique involving the 11-12-μm brightness temperature difference (BTD) perform well for thin cirrus. We demonstrate that the 1.38- μm channel (and the 3.7-11-μm BTD at night) on MODIS, when combined with additional channels, is capable of decoupling thin surrounding cirrus from thicker ice clouds. This information may be useful for screening thin cirrus that is often falsely interpreted as light precipitation. Radiative transfer simulations are used to demonstrate the theoretical basis for the selected multispectral channel combinations, and examples involving daytime and nighttime Aqua overpasses are presented.