New Spectral Methods in Cloud and Aerosol Remote Sensing Applications

We present new remote sensing techniques that rely on spectral observations of clouds and aerosols in the solar wavelength range. As first example, we show that the uncertainty of cloud retrievals can be improved considerably by exploiting the spectral information around liquid water absorption features in the near-infrared wavelength range. This is illustrated with spectral transmittance data from the NOAA International Chemistry Experiment in the Arctic LOwer Troposphere (ICEALOT, 2008). In contrast to the reflected radiance, transmitted radiance is only weakly sensitive to cloud effective radius, and only cloud optical thickness can be obtained from the standard dual-channel technique. We show that effective radius and liquid water path can be reliably retrieved with the new spectral approach, and validate our results with microwave liquid water path measurements. As second example, we show how the combined effects of heterogeneous clouds, aerosols and the surface within one satellite pixel can be distinguished by means of their spectral signatures, and illustrate with a case from the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS, Houston, Texas, 2006), Large Eddy Simulations (LES) of polluted boundary layer clouds, and three-dimensional radiative transfer calculations.