Radiometric and Polarimetric data inter-comparison for the POlarimeter DEfinition EXperiment (PODEX)

In January and February of 2013, three polarimeters were flown on the high-altitude NASA ER-2 aircraft, which was based in Palmdale, California as part of the POlarimeter DEfinition EXperiment (PODEX). The Airborne Multi-angle SpectroPolarimeter Imager (AirMSPI), Passive Aerosol and Cloud Suite (PACS) and Research Scanning Polarimeter (RSP) all employ different methods to determine polarization. Furthermore, they have a variety of spectral channels, spatial scales, measurement geometries and radiometric and polarimetric accuracies. All of these factors contribute to a sensor design's ability to determine geophysical properties of relevance to the global climate. Field deployment of airborne instruments such as AirMSPI, PACS and RSP provide valuable information for the development of future orbital instruments, such as the Aerosols-Clouds-Ecosystems (ACE) mission described by the National Research Council's Decadal Survey. For example, the complex algorithms that retrieve aerosol and cloud optical properties from polarimeters rely on realistic assessments of measurement uncertainty. We therefore compare the radiometric and polarimetric fidelity of these instruments using simultaneously observed scenes from PODEX, with the ultimate goal of improving retrieval algorithms and guiding future instrument design.