Interferometric Multi-chromatic Analysis of Terrasar-x Data

The Multi-Chromatic Analysis, as introduced in [1], consists in performing a spectral decomposition of each image of an interferometric pair. Spectral decomposition is performed extracting sub-bands in range frequency domain, each extracted sub-band leading to a range sub-look of the observed scene, here named a chromatic view, centered on its own carrier frequency but at lower range resolution. From a single interferometric pair, one can then generate several interferometric pairs exploring the frequency band centered on the carrier frequency of the initial acquisitions. The interferometric phase of spectrally-stable scatterers evolves linearly with the sub-band central frequency, the slope being proportional to the absolute optical path difference. Unlike the standard “monochromatic” InSAR approach, this new multi-chromatic technique allows performing spatially independent and absolute phase unwrapping (PU). Potential applications for the study of spectrally-stable targets include topographic measurements, atmospheric research or urban monitoring. The technique appears optimally suited for the new generation of satellite sensors, which operate with large bandwidths to reach metric range resolution. Previous work on the subject has started demonstrating the practical feasibility of the technique by using a set of SAR data collected by the airborne AES-1 radar interferometer, operating at X-band by multi-channel electronics, which provides a total radar bandwidth of 400 MHz. This work presents first successful applications of the technique using TerraSAR-X Spotlight interferometric dataset acquired on the desert area of Ayers Rock (Australia), which satisfies the processing requirements derived from previous investigations. In particular, it was possible to validate the use of MCA for performing absolute PU as well as for height measurement on a pixel-by-pixel basis. However, height measurements still needs a calibration procedure through independent measurements (e.g. reference points) due to the impact of atmospheric signals as well as orbital errors. A height surface derived by MCA is presented and compared to the reference SRTM DEM.