Exploring HARP'2 Polarimetric Precision for NASA PACE Mission

MultiAngle Polarimeters (MAP) are widely regarded as a necessary improvement to long used heritage radiometers. MAP instruments have greatly enhanced information content, helping constrain the ill-posed retrieval problem of retrieving aerosol properties from a remote sensing platform. It has also been shown during the era of PARASOL that polarized content with combined radiometric content from MODIS further enhances the capabilities of both instruments. It is expected to be similar with OCI aboard PACE and its associated MAPs, HARP2 and SPEXone. The hope of the PACE team is for the MAPs to have an absolute polarimetric accuracy of 0.5%. Prior simulated sensitivity studies, data from PARASOL, and aircraft campaigns has shown marked improvement in aerosol retrieval accuracy when polarimetric measurement accuracy is between 1% and 0.2% for properties such as the fine mode aerosol size parameters, real refractive index, and single scattering albedo. Here, we will show that HARP2 can meet these expectations with its pre-launch calibration. Further, we will show unique features of its wide field-of-view (FOV) effect on polarization which must be considered for the full error propagation of the instrument and those using similar optics. Finally, we will briefly discuss plans for the on-orbit validation of the polarimetric accuracy of HARP2 via the use of ocean sunglint, cloud reflectance, and land surface evaluation.