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Information Retrieval

The development of new information product generation algorithms, their implementation in the context of actual or future spaceborne SAR missions, and finally their demonstration and validation are main tasks performed by the group. The development of performance analysis models for inversion and product generation algorithms and the design of innovative calibration techniques for ongoing, planned and future SAR missions - including the calibration of propagation distortions - are the core activities. Finally, the design and the evaluation of experiments in the frame of actual SAR missions for the demonstration of new applications, the support and validation of the performance modis and calibration algorithms complement the group activities. The group contributes to several international studies and participates actively in the science advisory teams of national, European and international SAR missions and mission proposals.

Examples of the actual activities are:

• Development of robust vertical vegetation structure estimators from a limited number of interferometric acquisitions. The availability of multiple polarimetric interferograms makes it possible to determine, not only forest height and the underlying ground topography, but also the vertical distribution of scatterers within the volume. The image below shows two such vertical profiles from the inversion of dual-baseline Pol-InSAR data at L-band acquired over the Traunstein test site. The structure information allows to separate between younger mixed and mature spruce forest stands.

Vertical scattering profiles obtained from the inversion of dual-baseline Pol-InSAR data at L-band over the Traunstein test site. The profiles allow to distinguish younger mixed from mature spruce stands.

• Design of generic ionospheric calibration schemes for the calibration of low frequency (L- and P-band) polarimetric and/or interferometric data sets. The exploitation of the entirety of the ionosphere signature induced on a given observation space was leading to the development of combined techniques characterised by an improved performance in terms of accuracy and/or stability. The image below shows the performance of the developed calibration schema on interferometric coherence of an ALOS-PalSAR interferogram acquired over Collville, Alaska.

Calibration of ionospheric effects on the interferometric coherence. From left to right: Pauli RGB composite, interferometric coherence (HH channel) before and after calibration. Test Site: Collville, Alaska, sensor: ALOS-PalSAR.

• TanDEM-X interferometric coherence calibration: The compensation of Signal-to-Noise (SNR) decorrelation contributions and the suppression of azimuth ambiguities in terms of interferometric phase and coherence bias are required for the application of any quantitative Pol-InSAR inversion technique. The image below shows the interferometric phase and coherence before and after the suppression of azimuth ambiguities.   

TanDEM-X interferometric phase and coherence before and after the suppression of azimuth ambiguities.