On the Angular Effect of Residual Clouds, Aerosols, and Sun-Glint in Clear-Sky IR Radiance Observations: Experimental analyses

This presentation continues an investigation into the zenith angular effect of cloud-contamination within “clear-sky” infrared (IR) radiance observations (obs) commonly used in the retrieval of environmental data records (EDRs) from hyper/ultraspectral sounders such as the Joint Polar Satellite System (JPSS) Cross-track Infrared Microwave Sounder Suite (CrIMSS). Because IR retrieval algorithms, including the CrIMSS EDR algorithm, operate on the premise of minimizing the difference between clear-sky observations and calculations (calc), it is ideally desired that systematic differences between obs and calc under well-characterized conditions be minimal. And because most environmental sensors must scan the earth surface to facilitate global coverage, this should include an unbiased agreement over the range zenith angles encountered. Results of sensitivity analyses (Nalli et al. 2012) are corroborated with analyses of hyperspectral microwindow observations against forward calculations based upon collocated dropsondes from intensive field campaigns, indicating that contamination by residual clouds and/or aerosols within clear-sky observations can have a measurable (on the order of hundreds of milliKelvins) concave-up impact (i.e., an increasing positive bias symmetric over the scanning range) on the angular agreement of observations with calculations. It is also found in aircraft experimental data that sun-glint can have a measurable impact on agreement between calc – obs in longwave IR microwindow channels on the same order of magnitude as residual cloud/aerosol contamination.