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Interferometric Synthetic Aperture Radar (SAR) Missions Employing Formation Flying

Microwaves & Radar Inst., German Aerosp. Center, Wessling, Germany
Proceedings of the IEEE (Impact Factor: 5.47). 06/2010; 98(5):816 - 843. DOI: 10.1109/JPROC.2009.2038948
Source: IEEE Xplore

ABSTRACT This paper presents an overview of single-pass interferometric Synthetic Aperture Radar (SAR) missions employing two or more satellites flying in a close formation. The simultaneous reception of the scattered radar echoes from different viewing directions by multiple spatially distributed antennas enables the acquisition of unique Earth observation products for environmental and climate monitoring. After a short introduction to the basic principles and applications of SAR interferometry, designs for the twin satellite missions TanDEM-X and Tandem-L are presented. The primary objective of TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement) is the generation of a global Digital Elevation Model (DEM) with unprecedented accuracy as the basis for a wide range of scientific research as well as for commercial DEM production. This goal is achieved by enhancing the TerraSAR-X mission with a second TerraSAR-X like satellite that will be launched in spring 2010. Both satellites act then as a large single-pass SAR interferometer with the opportunity for flexible baseline selection. Building upon the experience gathered with the TanDEM-X mission design, the fully polarimetric L-band twin satellite formation Tandem-L is proposed. Important objectives of this highly capable interferometric SAR mission are the global acquisition of three-dimensional forest structure and biomass inventories, large-scale measurements of millimetric displacements due to tectonic shifts, and systematic observations of glacier movements. The sophisticated mission concept and the high data-acquisition capacity of Tandem-L will moreover provide a unique data source to systematically observe, analyze, and quantify the dynamics of a wide range of additional processes in the bio-, litho-, hydro-, and cryosphere. By this, Tandem-L will be an essential step to advance our understanding of the Earth system and its intricate dynamics. Enabling technologies and techniques are described in detail. An ou-
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tlook on future interferometric and tomographic concepts and developments, including multistatic SAR systems with multiple receivers, is provided.

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    • "The SAR data for this study were acquired during the TanDEM-X mission over Central Kalimantan on December 21, 2010. The mode used is called bistatic mode and is applied for the operational TanDEM-X mission acquisitions (Krieger et al., 2010). Both sensors are able to transmit the electromagnetic wave with a phased-array X-band antenna having a carrier frequency of 9.65 GHz (Pitz & Miller, 2010), corresponding to a wavelength of ~3.1 cm. "
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    • "Fig. 2. A parabolic reflector focuses an arriving plane wave on one or a small subset of feed elements. As the swath echoes arrive as plane waves from increasing look angles, one needs hence to only read out one feed element after the other to steer a high-gain beam in concert with the arriving echoes [9], [21], [22], [29]. A drawback of the multibeam mode is the presence of blind ranges across the swath, as the radar cannot receive while it is transmitting. "
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