A Pilot Study of Spectral Finger Prints and Information Content in the Hyperspectral Measurements for Absorbing Aerosols above Water Clouds

The absorbing aerosols heat the atmosphere by absorbing solar radiation, and such heating is enhanced when the aerosol layer is above liquid water cloud layer. Hence, to reduce the uncertainty in estimate of aerosol radiative forcing globally, it is required to use satellite remote sensing measurements to fully characterize the size, index of refraction, optical depth, and height of absorbing aerosols as well as the droplet size and optical depth of the underlying water cloud layer. While past work of using MODIS, OMI and CALIOP data have made good progress toward such characterization, it remains unclear if radiatively important parameters of aerosol and clouds can be fully retrieved simultaneously from hyperspectral measurement in UV to middle-wave infrared (up to 4 um). Here, we pursuit to answer this question by first conducting forward calculation with a start-of-science radiative transfer code to generate synthetic data for such a hypothetical hyperspectral measurement, and then by conducting the analysis of spectral finger prints and information content of absorbing aerosols and clouds in the synthetic data. Preliminary results reveal that such hyperspectral measurements have nearly 80% more information content than MODIS-type instrument in terms of degree of freedom for signal, especially for size and spectral dependence of optical depth of absorbing aerosols, although information content for absorbing aerosol optical depth and the height of absorbing aerosols are also increased to certain degree. The increase of information content for water cloud optical depth and effective radius remains minimal, but the increase is significant for effective variance of water cloud droplet size.