Constructing Cloud Physical Structure Based on Radiation Data

Radars can actively detect cloud internal physical structure while radiometers can passively measure the integral radiation characteristics of clouds. This study uses cloud products from CloudSat (active detection) and AQUA (passive detection) during the period from 1 January 2007 to 31 December 2010 over the area (15°-45°N, 145°-165°E) to study the relationships between the variations of radiation characteristics and the physical structure characteristics of clouds. MODIS (MODerate-resolution Imaging Spectroradiometer) uses 22 wavebands that have various sensitivities to cloud physical properties to measure radiation from cloud. Firstly, 13 wavebands demonstrating high correlation with the cloud physical structures are screened out based on correlation analysis. Then, the relationship between the radiation variations of these 13 wavebands and changes in the cloud physical structures are studied. Statistical analysis shows that the variation in cloud radiation illustrates a monotonic change with the variation in cloud physical structures when conditions (e.g., atmospheric environment, surface characteristics) change little. This means two cloud profiles with close radiative properties may also have similar physical structures. For some cloud profiles with unknown internal structures, their vertical structures can be inferred from other cloud profiles with similar spectral radiative properties. Preliminary tests for reconstructing the cloud vertical structure are performed and it is found that cloud physical structures constructed based on the nearest radiative characteristics principle are close to the structures measured by radars.