TerraSAR-X Capabilities in Polar Regions

DLR participates in a coordinated plan established by the space agencies for the optimum use of SAR acquisitions over the Artic and Antarctica for the remaining period of IPY and beyond. Due to the specific advantages of the X-band in respect to snow and ice properties and the high spatial resolution of the data, the contribution of TerraSAR-X focuses on topics like mapping of seasonal snow cover at high latitudes, ice sheet velocity, velocity fields of slow and fast moving glaciers, permafrost, generation of DEMs, sea ice classification. These are reflected in a coordinated proposal which is prepared by DLR and the scientific community as part of the common polar SAR acquisition plan

River Run Off Measurement With SAR Along Track Interferometry

The paper summarizes the need for global space borne river run-off measurements. It reports about an airborne SAR experiment aimed to measure the surface velocity of the river Isar in Bavaria / Germany. The results from two different SAR techniques, including Along Track Interferometry (ATI) show good correspondence. Finally suggestions for further studies are given

Detecting Building Layovers in a SAR Interferometric Processor Without External References

A novel technique for the derivation of building layovers is presented. It makes use of the behaviour of the geocoding processing stage embedded in an interferometric SAR processor for this particular case. It is shown how layover pixels create a regular pattern in the range mapping matrices, with a multiple mapping of a single SAR pixel for different DEM cells. The exploitation of these patterns yields a generation of a layover map without the use of external supports. The integration in an interferometric processor with a limited additional computational load and the capability to isolate building signatures are additional benefits. The algorithm is tested on a TanDEM-X spotlight acquisition over Berlin (Germany)

An Interferometric SAR Satellite Mission

The paper provides a critical review of the achievements in SAR interferometry from the ERS mission as well as from the Shuttle Radar Topography Mission SRTM. It describes the development from the original idea of the Interferometric Cartwheel to the concept of a formation flight of identical and active SAR satellites. From the experience gained from ERS and SRTM interferometric data processing as well as from the analysis of the Cartwheel concept a list of mission requirements has been set up. The most demanding one is the autonomous configuration flight of a tight x-band constellation, where the satellites fly as close as up to 30 m with a dead-band of +/- 10 m. The guidance, navigation and control considerations come to the conclusion that such a mission is feasible

Velocities of Major Outlet Glaciers of the Patagonia Icefield Observed by TerraSAR-X

The capabilities of TerraSAR-X data for feature tracking by amplitude correlation over glacier surfaces are investigated. Methodical aspects of the amplitude correlation approach are described. The TerraSAR-X based velocity fields are compared with former InSAR derived velocities and field measurements on three outlet glaciers on the South Patagonia ice field

First TerraSAR-X interferometry evaluation

The German radar satellite TerraSAR-X was launched in June 2007 [1] and is currently ending its commissioning phase. We anticipate quite different interferometric application scenarios compared to ERS- 1/2 and ASAR due to the X-band frequency, the short orbital repeat cycles of 11 days, the high range resolution and the spotlight mode of this sensor. During the commissioning phase we have scheduled a number of acquisitions over selected test sites with different characteristics to get an early quick look of TerraSAR-X's interferometric capabilities and to assess the phase quality of the sensor and DLR’s processor system [2]. Our first results are quite encouraging and the technical parameters of the system are as specified. Many spectacular image details let us expect that the high resolution will demand a different view on SAR interferometry and allow new applications in urban environments. In our paper we show interferograms and images of different test sites, coherence measurements and a first assessment of the interferometric properties. We will give hints to future scientific users on data selection and data processing. The results are of high relevance for the TanDEM-X mission scheduled for 2009, when a second compatible SAR-sensor will be launched for a joint 3 year bistatic interferometric formation flight

Geodetic Stereo SAR With Small Multi-Directional Radar Reflectors

This paper evaluates the applicability and achievable SAR accuracy for octahedrons – a combination of eight corner reflectors with a common phase centre. In an experiment at the observatory in Wettzell from July to November 2015 these cost-efficient and mobile radar targets were measured with TerraSAR-X Staring Spotlight and High-Resolution Spotlight. Applying the geodetic stereo SAR concept, octahedrons are very robust for absolute 3D positioning through their backscattering in multiple directions. Using octahedrons with as size of 47 cm, we achieve 3σ standard deviations of about 3 cm for east, north and height components. For individual measurements in Staring Spotlight the standard deviation shows 1.4 cm in range and 3.2 cm in azimuth

Toward Operational Compensation of Ionospheric Effects in SAR Interferograms: The Split-Spectrum Method

The differential ionospheric path delay is a major error source in L-band interferograms. It is superimposed to topography and ground deformation signals, hindering the measurement of geophysical processes. In this paper, we proceed toward the realization of an operational processor to compensate the ionospheric effects in interferograms. The processor should be robust and accurate to meet the scientific requirements for the measurement of geophysical processes, and it should be applicable on a global scale. An implementation of the split-spectrum method, which will be one element of the processor, is presented in detail, and its performance is analyzed. The method is based on the dispersive nature of the ionosphere and separates the ionospheric component of the interferometric phase from the nondispersive component related to topography, ground motion, and tropospheric path delay. We tested the method using various Advanced Land Observing Satellite Phased-Array type L-band synthetic aperture radar interferometric pairs with different characteristics: high to low coherence, moving and nonmoving terrains, with and without topography, and different ionosphere states. Ionospheric errors of almost 1 m have been corrected to a centimeter or a millimeter level. The results show how the method is able to systematically compensate the ionospheric phase in interferograms, with the expected accuracy, and can therefore be a valid element of the operational processor

Potential of global SAR positioning for geodetic applications - Lessons learned from TerraSAR-X and Sentinel-1

With our implementation of geodetic techniques for data processing and data corrections, spaceborne Synthetic Aperture Radar (SAR) has attained the possibility of fixing global positions of dedicated radar points at the low centimeter accuracy level. Such points can be created by passive radar corner reflectors, and the positioning method relies on the inherent ranging capabilities of SAR sensors. Thus, we may refer to the method as SAR imaging geodesy or geodetic SAR. Determining accurate long-term global positions of objects on the Earth’s surface is typically associated with Global Navigation Satellite Systems (GNSS) and one of the core elements of modern space geodesy. In order to do so, high-grade geodetic equipment with constant power supply, as well as the possibility for data transfer are required, limiting dense application on a large scale and poses difficulties for very remote areas with little or no infrastructure. Whereas certain regions like Japan or the San Andreas Fault are densely covered by GNSS such coverage may not be achievable everywhere on the globe. To improve the situation, we present a concept of jointly using SAR and GNSS for expanding geodetic positioning to applications requiring long-term coordinate monitoring. In future, the use of cost-effective passive reflectors in X-band SAR or low-cost battery-powered active transponders, which are currently in development for C-band SAR, could provide global coordinates anywhere where SAR imagery is acquired under multiple incidence angles. The main requirements are precise orbit determination, processing of the SAR imagery omitting geometric approximations, as well as the rigorous correction of perturbations caused by atmospheric path delay and signals of the dynamic Earth. If a reflector or transponder already has known reference coordinates, e.g. from co-location with GNSS, the perturbing signals can be mitigated for the surrounding radar points by applying differential SAR positioning techniques similar to differential GNSS, provided that all the points are included in the same radar image. In this contribution we discuss the geodetic SAR methods with respect to our experiences gained with the TerraSAR-X mission, and present first results of experiments carried out with Sentinel-1 data