An evaluation of the liquid cloud droplet effective radius derived from MODIS, airborne remote sensing, and in situ measurements from CAMP.sup.2Ex

The cloud drop effective radius (R.sub.e) of the drop size distribution derived from passive satellite sensors is a key variable used in climate research. Validation of these satellite products has often taken place under stratiform cloud conditions that favor the assumption of cloud horizontal homogeneity used by the retrieval techniques. However, many studies have noted concerns with respect to significant biases in retrieved R.sub.e arising from cloud heterogeneity, for example, in cumulus cloud fields. Here, we examine data collected during the 2019 "Cloud, Aerosol and Monsoon Processes Philippines Experiment" (CAMP.sup.2 Ex), which, in part, targeted the objective of providing the first detailed evaluation of R.sub.e retrieved across multiple platforms and techniques in a cumulus and congestus cloud region. Our evaluation consists of cross-comparisons of R.sub.e between the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra satellite, the Research Scanning Polarimeter (RSP) onboard the NASA P-3 aircraft, and in situ measurements from both the NASA P-3 and Learjet aircraft that are all taken in close spatiotemporal proximity to the same cloud fields. A particular advantage of our approach lies in the capability of the RSP to retrieve R.sub.e using a bi-spectral MODIS approach and a polarimetric approach, which allows for the evaluation of bi-spectral and polarimetric R.sub.e retrievals from an airborne perspective using the same samples.