Retrieving Cloud Fraction in the Field-of-View of a High-Spectral Resolution Infrared Radiometer

The combination of radiance from both clear and cloudy regions of sky within the instrument's field of view (FOV) adds significant uncertainty to retrievals of atmospheric state profiles and cloud microphysical properties from infrared spectroradiometers. We use observations of radiance from both the 8-13 and 3-5 μm bands to retrieve estimates of the cloud fraction in the instrument's FOV, as well as microphysical cloud properties, from high-spectral-resolution infrared radiometers. Cloud fraction derived from imagers as well as high-time-resolution observations show good agreement and high correlation with our derived cloud fraction values. This is shown for both ground-based and aircraft-based observations. We also demonstrate that the use of the additional information in the 3-5 μm band extends the dynamic range and accuracy of microphysical properties that can be retrieved from infrared radiance data.