Integration model of POSP measurement spatial response function.

The particulate observing scanning polarimeter (POSP) measurement spatial response function (SRF) relates to the weighted contribution of each location within the measurement footprint, which is determined by the percentage of the dwell time of each location on the Earth surface to the overall sampling integration time. The SRF resulting from a combination of the equally weighted instantaneous field of view (IFOV) during integration is required for an accurate modeling. Simply using a mean value SRF assuming an equivalent weight at each sampling position instead of the actual SRF will inevitably introduce errors. Considering the data fusion between POSP and high spatial resolution sensors, a discrete integration method that takes the effect of actual weights into account is proposed in this paper. The simulation results of the integral model and the mean value model show that the larger the intensity change in the sampling area covered by the IFOV of the POSP during a single sampling, the more significant the difference between the two results. Meanwhile, the integration SRF is validated by resampling the simultaneous imaging polarization camera (SIPC) data, which is compared with POSP data acquired at the same time in an aerial experiment. The results show that the integration SRF model is more accurate to characterize the details of POSP measurement than the mean value SRF model. The proposed SRF reduces the root mean square error (RMSE) of convolved results and measurements by 5∼30% with different radiance contrast scene.

Radiometer-to-imager in-flight cross calibration and verification.

This work develops a method to complete the in-flight cross calibration and verification between a radiometer and an imager hosted on aircraft. The in-flight cross calibration is data transmission through time matching, space matching, and spectral matching of two polarization instruments on the same platform, and this method can not only complete the data transfer without considering the surface type to reduce the calibration cycle but also can obtain huge and rich calibration data. The radiometer is the particulate observing scanning polarimeter (POSP), which takes multi-angle, photo-polarimetric measurements in several spectral channels. The POSP measurements in the bands of 670nm and 865nm used in this work are simultaneously measured by the simultaneous imaging polarization camera (SIPC), which is on the same aircraft. The POSP is designed to provide high precision measurements of the atmospheric or earth surface radiation polarization with a substantial along-track spatial coverage, while the SIPC can provide large spatial coverage and high-resolution measurements. Through radiometer-to-imager in-flight cross calibration, the high-precision calibration coefficient of the POSP is transmitted to the SIPC, which can effectively improve the measurement accuracy of the SIPC, and realizes the remote sensing monitoring of atmospheric fine particles with large spatial coverage and high detection precision. First, we deduce the polarization models of the POSP and the SIPC, respectively, and express them in the form of Mueller matrixes, which describe the transformation from incoming polarized radiation to measured signals. Then, we deduce the in-flight cross calibration model of the POSP and the SIPC. Finally, the in-flight experiments have been carried out to validate the radiometer-to-imager in-flight cross calibration model. The results have shown the possibility to minimize the SIPC polarization degree errors with a roughly 0.01 bias relative to POSP on the land.