On the Use of Transponders as Coherent Radar Targets for SAR Interferometry

Mahapatra, P.; Samiei-Esfahany, Sami; Marel, H. van der; Hanssen, Ramon F.

doi:10.1109/tgrs.2013.2255881

Cited by 34 publications

(36 citation statements)

References 24 publications

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“…Compact, active transponders (as described by [13]) are an alternative type of artificial target to corner reflectors that can be deployed readily in geodetic networks and utilised with C-band sensors such as Sentinel-1 and RSAT-2. The clear advantage of these transponders over passive corner reflectors is that they are consistently compact and therefore less obtrusive in the environment and more easily coupled (due to their small size) to other geodetic monumentation for cross-validation of signals.…”

Section: Discussionmentioning

confidence: 99%

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

Garthwaite

2017

Remote Sensing

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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.

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Section: Discussionmentioning

confidence: 99%

“…However, in non-urban areas the distribution of PS may be much sparser, or even non-existent. Consequently, artificial targets are increasingly being deployed in the field to introduce coherent point targets in regions where naturally occurring PS are sparse or non-existent (e.g., [6][7][8][9][10][11][12][13][14]). …”

Section: Introductionmentioning

confidence: 99%

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

Garthwaite

2017

Remote Sensing

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“…However, the transformation to geographical coordinates, which is based here on ground control points, causes a reduction of the precision in the final product, which is compared to the in-situ measurements. To improve positioning in future work, a satellite orbit and Digital Elevation Model (DEM)-based geolocalization procedure will be evaluated, in combination with a radar corner reflector/transponder with Global Navigation Satellite System (GNSS)-measured location to remove orbit and timing errors [50]. Alternatively, the performance when using the annotated geolocalization parameters in the Terra-SAR-X products should be evaluated.…”

Section: Methods Improvementmentioning

confidence: 99%

Semi-Automated Monitoring of a Mega-Scale Beach Nourishment Using High-Resolution TerraSAR-X Satellite Data

et al. 2017

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This paper presents a semi-automated approach to detecting coastal shoreline change with high spatial-and temporal-resolution using X-band synthetic aperture radar (SAR) data. The method was applied at the Sand Motor, a "mega-scale" beach nourishment project in the Netherlands. Natural processes, like waves, wind, and tides, gradually distribute the highly concentrated sand to adjacent beaches. Currently, various in-situ techniques are used to monitor the Sand Motor on a monthly basis. Meanwhile, the TerraSAR-X satellite collects two high-resolution (3 × 3 m), cloud-penetrating SAR images every 11 days. This study investigates whether shorelines detected in TerraSAR-X imagery are accurate enough to monitor the shoreline dynamics of a project like the Sand Motor. The study proposes and implements a semi-automated workflow to extract shorelines from all 182 available TerraSAR-X images acquired between 2011 and 2014. The shorelines are validated using bi-monthly RTK-GPS topographic surveys and nearby wave and tide measurements. A valid shoreline could be extracted from 54% of the images. The horizontal accuracy of these shorelines is approximately 50 m, which is sufficient to assess the larger scale shoreline dynamics of the Sand Motor. The accuracy is affected strongly by sea state and partly by acquisition geometry. We conclude that using frequent, high-resolution TerraSAR-X imagery is a valid option for assessing coastal dynamics on the order of tens of meters at approximately monthly intervals.

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“…A stable radar scatterer (i.e. a PS) such as a transponder (Fromberg 2014;Mahapatra et al 2014;) is physically connected to a GNSS antenna as shown in Fig. 1, ensuring that they experience the same displacements.…”

Section: Ps-gnss Collocationmentioning

confidence: 99%

“…Small and lightweight PS such as compact active transponders (CATs) (Fromberg 2014;Mahapatra et al 2014; are installed and used as InSAR reference points. Their phase stability has been shown in Mahapatra et al (2014) and to be comparable to that of corner reflectors up to a few millimetres. Each transponder is rigidly attached to a GNSS antenna; the displacement of the InSAR reference point is therefore precisely measured through GNSS in a standard TRF.…”

Section: Introductionmentioning

confidence: 99%