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Bistatic Interferometric toolkit for campaign evaluation and DEM generation

Sergi Duque(1), Paco López-Dekker(1), Jordi J. Mallorqui(1) and Juan C. Merlano(1)

(1) UPC, Jordi Girona 1-3, 08034 Barcelona, Spain

Abstract

Sergi Duque, Paco López-Dekker, Jordi J. Mallorqui and Juan C. Merlano Universitat Politécnica de Catalunya Email: {sergi.duque,paco.dekker, mallorqui, juan.merlano}@tsc.upc.edu

Introduction In the last decades, Synthetic Aperture Radar (SAR) has been established as a standard tool for Earth Observation. Interferometric applications, such as InSAR or DInSAR, are reliable techniques for performing Digital Elevation Models (DEM) and for monitoring terrain deformations. These techniques are reaching maturity for monostatic geometries, where the transmitter and receiver are co-located. Bistatic and multistatic configurations, where the transmitter and receiver are located at different places, are arising as a new research field. Some of the upcoming systems, such as TanDEM-X mission, can be described as quasi-monostatic configuration, with the receiver and transmitter close each other and following almost parallel trajectories. In this paper a bistatic geometry, where the transmitter is onboard a satellite and the receiver is on the ground, and its interferometric applications are going to be considered. Study of bistatic interferometry Bistatic interferometry has been studied taking into account the different geometric configurations that are possible with our system. General expressions have been derived for the interferometric phase and coherence that include the effect of having two different baselines, one for the transmitter and the other one for the receiver. Different decorrelation factors, such as volumetric and geometric, have been studied for the bistatic case. As a result of the study of these theoretical aspects a bistatic interferometric simulator has been developed.

System description The Remote Sensing Lab at the Universitat Politècnica de Catalunya (UPC) has developed a C-band receiver for a groundbased bistatic SAR system using ESA’s ERS-2 and ENVISAT as transmitters of opportunity, which has been named SABRINA (SAR Bistatic Receiver for INterferometric Applications)[1] [2].. The current SABRINA system consists of a dual channel C-band front-end that amplifies and down-converts the received signals to video band, a dual channel high speed digitizer and a set of software tools to perform the bistatic SAR processing. For generating bistatic SAR images, one channel is connected to an antenna pointed at the satellite to obtain a clean direct signal which is used for synchronization and reference signal. The second channel is connected to an antenna directed at the region of interest. This system was originally designed for generating bistatic interferograms. As in the monostatic case, we can distinguish between two types of interferograms, single and dual pass.

Single pass: To acquire single pass interferometric data, the two channels have been connected to two antennas pointing at the region of interest and separated horizontally a specific baseline. In this configuration the signal of reference is extracted of one of the scattered channels through to antenna sidelobes. While preliminary single pass data has been presented in previous symposia, in this paper geocoded final products, such as a DEM is going to be presented. Also, a bistatic interfeometric toolkit is going to be discussed, highlighting the differences with the monostatic one. This toolkit includes corregistration, topography cancelation, unwrapping and geocoding tools, which take into account the fact that transmitter and receiver are located far away. The application of this set of interferometric tools to the acquired bistatic SAR images will provide an estimation of the terrain elevation. Quality assessment will be performed on this estimation, comparing it with external DEMs. The interferometric data will be produced from two different test-sites. The first one is an area close to UPC campus, which is a mixture between forrest an urban zones with predominant distributed targets. The second test-site will be an urban area.

Dual pass: We will also analyze a dual pass interferometric configuration. In this particular bistatic case the transmitter is a transmitter of opportunity, which means that we have have to deal with the lack of synchronism between transmitter and receiver. Although the direct signal is used to recover it, residual errors result in phase errors, that need to be studied. This problems are not present in the single pass configuration because most of the residual errors are common in the both images and they are canceled. This analysis will be illustrated real data sets.

[1] J Sanz-Marcos, P. Prats, J Mallorqui, and A. Aguasca. A subaperture range-doppler processor for bistatic-fixed-receiver sar. In EUSAR06. [2] J Sanz-Marcos, P. Lopez-Dekkes, J Mallorqui, A. Aguasca, and P. Pau. Sabrina: a sar bistatic receiver for interferometric applications. In IEEE Geoscience and Remote Sensing Letters.

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry