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Remote Sens. 2017, 9(7), 648; doi:10.3390/rs9070648

On the Design of Radar Corner Reflectors for Deformation Monitoring in Multi-Frequency InSAR

Geodesy and Seismic Monitoring Branch, Geoscience Australia, GPO Box 378, Canberra ACT 2601, Australia
Academic Editors: Timo Balz, Uwe Soergel, Mattia Crespi, Batuhan Osmanoglu and Prasad S. Thenkabail
Received: 19 April 2017 / Revised: 15 June 2017 / Accepted: 21 June 2017 / Published: 25 June 2017
(This article belongs to the Special Issue Advances in SAR: Sensors, Methodologies, and Applications)
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Abstract

Trihedral corner reflectors are being increasingly used as point targets in deformation monitoring studies using interferometric synthetic aperture radar (InSAR) techniques. The frequency and size dependence of the corner reflector Radar Cross Section (RCS) means that no single design can perform equally in all the possible imaging modes and radar frequencies available on the currently orbiting Synthetic Aperture Radar (SAR) satellites. Therefore, either a corner reflector design tailored to a specific data type or a compromise design for multiple data types is required. In this paper, I outline the practical and theoretical considerations that need to be made when designing appropriate radar targets, with a focus on supporting multi-frequency SAR data. These considerations are tested by performing field experiments on targets of different size using SAR images from TerraSAR-X, COSMO-SkyMed and RADARSAT-2. Phase noise behaviour in SAR images can be estimated by measuring the Signal-to-Clutter ratio (SCR) in individual SAR images. The measured SCR of a point target is dependent on its RCS performance and the influence of clutter near to the deployed target. The SCR is used as a metric to estimate the expected InSAR displacement error incurred by the design of each target and to validate these observations against theoretical expectations. I find that triangular trihedral corner reflectors as small as 1 m in dimension can achieve a displacement error magnitude of a tenth of a millimetre or less in medium-resolution X-band data. Much larger corner reflectors (2.5 m or greater) are required to achieve the same displacement error magnitude in medium-resolution C-band data. Compromise designs should aim to satisfy the requirements of the lowest SAR frequency to be used, providing that these targets will not saturate the sensor of the highest frequency to be used. Finally, accurate boresight alignment of the corner reflector can be critical to the overall target performance. Alignment accuracies better than 4° in azimuth and elevation will incur a minimal impact on the displacement error in X and C-band data. View Full-Text
Keywords: InSAR; persistent scatterers; geodesy; corner reflector; point target; interferometry; Synthetic Aperture Radar; calibration and validation InSAR; persistent scatterers; geodesy; corner reflector; point target; interferometry; Synthetic Aperture Radar; calibration and validation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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Garthwaite, M.C. On the Design of Radar Corner Reflectors for Deformation Monitoring in Multi-Frequency InSAR. Remote Sens. 2017, 9, 648.

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