Polarimetric Synthetic Aperture Radar (PolSAR) data has been extensively used in earth observation for scattering-based biophysical and geophysical parameters retrieval in different thematic applications. Several spaceborne SAR satellites have been launched, and many more sensors in different frequency ranges are scheduled and are yet to be launched into space by space agencies. The increased demand for the polarimetric SAR data and the state-of-the-art sensors that are planned in future missions require assurance about the distortion-free data for accurate backscatter information retrieval. Any error in PolSAR-based backscatter information retrieval for thematic applications will give inaccurate modelled output, so the distortion-free data is an essential requirement for accurate output. Polarimetric calibration (PolCal) is essential to minimize distortions from airborne and spaceborne SAR data for scattering-based characterization of the targeted objects. The present study investigates the polarimetric distortions in the L-and S-band airborne dual-frequency SAR data. The L- and S-band airborne SAR (LS-ASAR) is a precursor mission of the spaceborne dual-frequency L- and S-band NASA ISRO Synthetic Aperture Radar (NISAR). The present work utilizes the LS-ASAR data acquired over the Rosamond Corner Reflector Array (RCRA). Five corner reflectors (CRs) of 4.8-meter side-length were oriented to measure the backscatter responses from the CRs in L-and S-band SAR data. To analyze the polarimetric distortions in the SAR data, scatterplots were plotted for co-pol and cross-pol channels of the PolSAR scattering matrix. The correlation between cross-polarimetric combinations (HV and VH) should be very high for a perfectly calibrated monostatic SAR system. A linear trend will be obtained from the scatterplot for the backscatter values of HV and VH channels of polarimetrically calibrated SAR data. The scatterplot between HV and VH channels of LS-ASAR data shows that the backscatter values of HV and VH channels are equal. The scatterplot between the HV and VH channels of the LS-ASAR data shows that the backscatter values of the HV and VH channels are similar. The most efficient way to evaluate polarimetric distortions of SAR data is the analysis of polarimetric signatures of the backscatter responses for field-located corner reflectors that were mounted during SAR data acquisition. The polarimetric signature analysis of co-pol and cross-pol channels shows that the co-pol signature shows perfect behaviour. Still, the polarimetric distortions could be easily seen in the cross-pol signatures.
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Polarimetric distortion analysis of L- and S-band airborne SAR (LS-ASAR): A precursor study of the spaceborne dual-frequency L- and S-band NASA ISRO Synthetic Aperture Radar (NISAR)
Published: 01 November 2022 by MDPI in 9th International Electronic Conference on Sensors and Applications session Remote Sensing
Keywords: LS-ASAR; NISAR; Polarimetric Distortions; Polarimetric Calibration (PolCal); Polarimetric Signature