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Mitigation of atmospheric perturbations and solid Earth movements in a TerraSAR-X time-series


Schubert, A; Jehle, M; Small, D; Meier, E (2012). Mitigation of atmospheric perturbations and solid Earth movements in a TerraSAR-X time-series. Journal of Geodesy, 86(4):257-270.

Abstract

The TerraSAR-X (TSX) synthetic aperture radar (SAR) marks the recent emergence of a new generation of spaceborne radar sensors that can for the first time lay claim to localization accuracies in the sub-meter range. The TSX platform’s extremely high orbital stability and the sensor’s hardware timing accuracy combine to enable direct measure- ments of atmospheric refraction and solid Earth movements. By modeling these effects for individual TSX acquisitions, absolute pixel geolocation accuracy on the order of several centimeters can be achieved without need for even a single tiepoint. A 16-month time series of images was obtained over a fixed test site, making it possible to validate both an atmo- spheric refraction and a solid Earth tide model, while at the same time establishing the instrument’s long-term stability. These related goals were achieved by placing trihedral cor- ner reflectors (CRs) at the test site and estimating their phase centers with centimeter-level accuracy using differential GPS (DGPS). Oriented in pairs toward a given satellite track, the CRs could be seen as bright “points” in the images, provid- ing a geometric reference set. SAR images from the high- resolution spotlight (HS) mode were obtained in alternating ascending and descending orbit configurations. The high- est-resolution products were selected for their small sample dimensions, as positions can be more precisely determined. Based on the delivered product annotations, the CR imagepositions were predicted, and these predictions were com- pared with their measured image positions both before and after compensation for atmospheric refraction and systematic solid Earth deviations. It was possible to show that when the atmospheric distortion and Earth tides are taken into account, the TSX HS products have geolocation accuracies far exceed- ing the specified requirements. Furthermore, this accuracy was maintained for the duration of the 16-month test period. It could be demonstrated that with a correctly calibrated sen- sor, and after accounting for atmospheric and tidal effects, tiepoint-free geolocation is possible with TSX with an abso- lute product accuracy of about 5 cm.

Abstract

The TerraSAR-X (TSX) synthetic aperture radar (SAR) marks the recent emergence of a new generation of spaceborne radar sensors that can for the first time lay claim to localization accuracies in the sub-meter range. The TSX platform’s extremely high orbital stability and the sensor’s hardware timing accuracy combine to enable direct measure- ments of atmospheric refraction and solid Earth movements. By modeling these effects for individual TSX acquisitions, absolute pixel geolocation accuracy on the order of several centimeters can be achieved without need for even a single tiepoint. A 16-month time series of images was obtained over a fixed test site, making it possible to validate both an atmo- spheric refraction and a solid Earth tide model, while at the same time establishing the instrument’s long-term stability. These related goals were achieved by placing trihedral cor- ner reflectors (CRs) at the test site and estimating their phase centers with centimeter-level accuracy using differential GPS (DGPS). Oriented in pairs toward a given satellite track, the CRs could be seen as bright “points” in the images, provid- ing a geometric reference set. SAR images from the high- resolution spotlight (HS) mode were obtained in alternating ascending and descending orbit configurations. The high- est-resolution products were selected for their small sample dimensions, as positions can be more precisely determined. Based on the delivered product annotations, the CR imagepositions were predicted, and these predictions were com- pared with their measured image positions both before and after compensation for atmospheric refraction and systematic solid Earth deviations. It was possible to show that when the atmospheric distortion and Earth tides are taken into account, the TSX HS products have geolocation accuracies far exceed- ing the specified requirements. Furthermore, this accuracy was maintained for the duration of the 16-month test period. It could be demonstrated that with a correctly calibrated sen- sor, and after accounting for atmospheric and tidal effects, tiepoint-free geolocation is possible with TSX with an abso- lute product accuracy of about 5 cm.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Geography
Dewey Decimal Classification:910 Geography & travel
Language:English
Date:2012
Deposited On:01 Nov 2011 15:52
Last Modified:05 Apr 2016 15:04
Publisher:Springer
ISSN:0949-7714
Publisher DOI:https://doi.org/10.1007/s00190-011-0515-6

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