A Three-Hierarchy Evaluation of Polarimetric Performance of GF-3, Compared with ALOS-2/PALSAR-2 and RADARSAT-2.

Zezhong Wang,Qiming Zeng,Junyi Liu,Jian Jiao

doi:10.3390/s19071493

Abstract

GaoFen-3 (GF-3) is the first Chinese civilian multi-polarization synthetic aperture radar (SAR) satellite, launched on 10 August of 2016, and put into operation at the end of January 2017. The polarimetric SAR (PolSAR) system of GF-3 is able to provide quad-polarization (quad-pol) images in a variety of geophysical research and applications. However, this ability increases the complexity of maintaining image quality and calibration. As a result, to evaluate the quality of polarimetric data, polarimetric signatures are necessary to guarantee accuracy. Compared with some other operational space-borne PolSAR systems, such as ALOS-2/PALSAR-2 (ALOS-2) and RADARSAT-2, GF-3 has less reported calibration and image quality files, forcing users to validate the quality of polarimetric imagery of GF-3 before quantitative applications. In this study, without the validation data obtained from a calibration infrastructure, an innovative, three-hierarchy strategy was proposed to assess PolSAR data quality, in which the performance of GF-3 data was evaluated with ALOS-2 and RADARSAT-2 data as references. Experimental results suggested that: (1) PolSAR data of GF-3 satisfied backscatter reciprocity, similar with that of RADARSAT-2; (2) most of the GF-3 PolSAR images had no signs of polarimetric distortion affecting decomposition, and the system of GF-3 may have been improved around May 2017; and (3) the classification accuracy of GF-3 varied from 75.0% to 91.4% because of changing image-acquiring situations. In conclusion, the proposed three-hierarchy approach has the ability to evaluate polarimetric performance. It proved that the residual polarimetric distortion of calibrated GF-3 PolSAR data remained at an insignificant level, with reference to that of ALOS-2 and RADARSAT-2, and imposed no significant impact on the polarimetric decomposition components and classification accuracy.

Highlights

GaoFen-3 (GF-3) was launched on 10 August of 2016 and was put into operation at the end of January, 2017 [1]
polarimetric SAR (PolSAR) images had no signs of polarimetric distortion affecting decomposition, and the system of GF-3 may have been improved around May 2017; and (3) the classification accuracy of GF-3 varied from 75.0% to 91.4% because of changing image-acquiring situations
The proposed three-hierarchy approach has the ability to evaluate polarimetric performance. It proved that the residual polarimetric distortion of calibrated GF-3 PolSAR data remained at an insignificant level, with reference to that of ALOS-2 and RADARSAT-2, and imposed no significant impact on the polarimetric decomposition components and classification accuracy

Summary

Introduction

GaoFen-3 (GF-3) was launched on 10 August of 2016 and was put into operation at the end of January, 2017 [1] It is the first Chinese space-borne multi-polarization co-/cross-imaging radar mission in C-band, with a fully polarimetric quad-polarization (quad-pol) mode [2]. The quad-pol mode provides data with at least 40 beams and ground range resolutions of about 8 m and 25 m [3] These polarimetric data are expected to be substantially applied in sea and ocean monitoring, disaster reduction, water conservancy, and meteorology [4]. The performance of these applications depends extremely on the polarimetric fidelity. Despite the introduction of the synthetic aperture radar (SAR) payload design and the report of in-orbit tests and Sensors 2019, 19, 1493; doi:10.3390/s19071493 www.mdpi.com/journal/sensors

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Conclusion