Recent advances in extra-wide-band polarimetry, interferometry and polarimetric interferometry in synthetic aperture remote sensing and its applications

Abstract

The development of radar polarimetry and radar interferometry is advancing rapidly, and these novel radar technologies are revamping ‘Synthetic aperture radar imaging’ decisively. The successive advancements are sketched – beginning with the fundamental formulations and highlighting the salient points of these diverse remote sensing techniques. Whereas with radar polarimetry the textural fine-structure, target orientation and shape, symmetries and material constituents can be recovered with considerable improvements above that of standard ‘amplitude-only polarisation radar’; with radar interferometry the spatial (in depth) structure can be explored. In ‘polarimetric–interferometric synthetic aperture radar (POL-IN-SAR) imaging’ it is possible to recover such co-registered textural plus spatial properties simultaneously. This includes the extraction of ‘digital elevation maps (DEM)’ from either ‘fully polarimetric (scattering matrix)’ or ‘interferometric (dual antenna) SAR image data takes’ with the additional benefit of obtaining co-registered three-dimensional ‘POL-IN-DEM’ information. Extra-wide-band POL-IN-SAR imaging – when applied to ‘repeat-pass image overlay interferometry’ – provides differential background validation and measurement, stress assessment, and environmental stress-change monitoring capabilities with hitherto unattained accuracy, which are essential tools for improved global biomass estimation and also for wetland assessment and monitoring. More recently, by applying multiple parallel repeat-pass EWB-POL-D(RP)-IN-SAR imaging along stacked (altitudinal) or displaced (horizontal) flight-lines will result in ‘tomographic (multi-interferometric) polarimetric SAR stereo-imaging’, including foliage- and ground-penetrating capabilities. In addition, various closely related topics of (i) acquiring additional and protecting existing spectral windows of the ‘natural electromagnetic spectrum (NES)’ pertinent to remote sensing; and (ii) mitigation against common ‘radio frequency interference (RFI)’ and intentional ‘directive jamming of airborne and spaceborne POL-IN-SAR imaging platforms’ are appraised.