Need for developing repeat-pass differential POLSAR interferometry

Radar Polarimetry, Radar Interferometry and Polarimetric SAR Interferometry represent the current culmination in active ´Microwave Remote Sensing´ technology, but we still need to progress very considerably in order to reach the limits of physical realizability. Whereas with radar polarimetry the textural fine-structure, target orientation, symmetries and material constituents can be recovered with considerable improvement above that of standard ´amplitude-only´ radar; by implementing ´radar interferometry´ the spatial (in depth) structure can be explored. With Polarimetric Interferometric Synthetic Aperture Radar (POL-IN-SAR) imaging, it is possible to recover such co-registered textural and spatial information from POL-IN-SAR digital image data sets simultaneously, including the extraction of Digital Elevation Maps (DEM) from either Polarimetric (scattering matrix) or Interferometric (dual antenna) SAR systems. Simultaneous Polarimetric-plus- Interferometric SAR Imaging offers the additional benefit of obtaining co-registered textural-plus-spatial three-dimensional POL-IN-DEM information, which when applied to Repeat-Pass Image-Overlay Interferometry provides differential background validation and environmental stress-change information with highly improved accuracy. However, hitherto only single-polarization-channel repeat-pass IN-SAR was developed and considered; and therefore the aim of this paper is to scrutinize and determine why and for what specific problems fully polarimetric differential RP-POL-IN-SAR imaging is required.