Hybrid Dual-Polarization Synthetic Aperture Radar

Abstract

Compact polarimetry for a synthetic aperture radar (SAR) system is reviewed. Compact polarimetry (CP) is intended to provide useful polarimetric image classifications while avoiding the disadvantages of space-based quadrature-polarimetric (quad-pol) SARs. Two CP approaches are briefly described, π/4 and circular. A third form, hybrid compact polarimetry (HCP) has emerged as the preferred embodiment of compact polarimetry. HCP transmits circular polarization and receives on two orthogonal linear polarizations. When seen through its associated data processing and image classification algorithms, HPC’s heritage dates back to the Stokes parameters (1852), which are summarized and explained in plain language. Hybrid dual-polarimetric imaging radars were in the payloads of two lunar-orbiting satellites, India’s Earth-observing RISAT-1, and Japan’s ALOS-2. In lunar or planetary orbit, a satellite equipped with an HCP imaging radar delivers the same class of polarimetric information as Earth-based radar astronomy. In stark contrast to quad-pol, compact polarimetry is compatible with wide swath modes of a SAR, including ScanSAR. All operational modes of the SARs aboard Canada’s three-satellite Radarsat Constellation Mission (RCM) are hybrid dual-polarimetric. Image classification methodologies for HCP data are reviewed, two of which introduce errors for reasons explained. Their use is discouraged. An alternative and recommended group of methodologies yields reliable results, illustrated by polarimetrically classified images. A survey over numerous quantitative studies demonstrates HCP polarimetric classification effectiveness. The results verify that the performance accuracy of the HCP architecture is comparable to the accuracy delivered by a quadrature-polarized SAR. Four appendices are included covering related topics, including comments on inflight calibration of an HCP radar.

RADARSAT Constellation Mission’s Operational Polarimetric Modes: A User-Driven Radar Architecture

“…Knowledge of the complete scattering matrix is not needed. Contrary to the convictions of many practitioners, when classified appropriately, HCP data delivers results that are comparable to those from the most popular and effective decomposition tools applied to quad-pol SAR data (Charbonneau et al 2010;Buckley and Smith 2016;Raney 2019;Brisco et al 2020).…”

“…Souyris et al 2005). Such expansions can only degrade the intended result (Raney 2019;Brisco et al 2020). There are two fundamental reasons for this fact: (i) The supposed scattering matrix elements available from RCM's HCP radars are (L)H, (L)V (Emmons and Alexander 1983) and their complex cross-product.…”

“…There are many examples of comparisons between FP and HCP classifications that illustrate their practical equivalence (Charbonneau et al 2010;Buckley and Smith 2016;Raney 2019;Brisco et al 2020). Note that these and all other studies that compare the performance of an HCP versus an FP polarimeter are empirical, based on their respective classification results.…”

Hyperspectral Molecular Orientation Mapping in Metamaterials

“…More recently, hybrid compact polarmetric (HCP) SAR satellites, which transmit circular polarisation and revive H and V, have been launched for both Earth and Lunar observations. This allows for all four Stokes parameters to be determined [9,10]. Hence, the state of polarisation of light is known upon reflection (scattering) from surface (interface).…”

General Two-Stage Model-Based Three-Component Hybrid Compact Polarimetric SAR Decomposition Method

“…C OMPACT Polarimetric Synthetic Aperture Radar (SAR) is a special dual-polarimetric system and has advantages of simple system design, halved transmission power and wider swath compared with quad-polarimetric SAR. It can obtain more scattering information than traditional linear dualpolarimetric SAR and sometimes achieve similar performance with quad-polarimetric SAR in many applications [1]. There are currently three different CP modes.…”