Factors Influencing the Calculation of Infrared Clear-Sky Brightness Temperatures for Satellite Retrievals of Cloud Properties

For decades, techniques for retrieving cloud properties using infrared and visible satellite radiances have been developed, refined, and applied to data from many satellite platforms, each having its own unique spectral channels and spectral response functions. The accuracy of these cloud property retrievals is critically dependent on an accurate assessment of clear-sky brightness temperatures. This study examines the different factors that influence the calculation of top of atmosphere (TOA) clear-sky brightness temperatures for 3 infrared channels commonly present on many satellite platforms and often used in cloud property retrievals: the solar infrared channel (around 3.9 μm), the infrared window channel (around 12 μm) and the split-window channel (around 12 μm). Of particular consideration will be the sensitivity of the TOA clear-sky brightness temperatures to instrument spectral response function, model skin temperature, and model profiles (including the possible presence of clouds in the model profile). The goal of this research is to understand and quantify the uncertainties present in the calculation of clear-sky brightness temperature, and how they translate into cloud property retrieval uncertainties. This will contribute towards the ultimate goal of providing spatially and temporally consistent global cloud products from multiple satellite platforms.