Thomas Krauß

Automated Georeferencing of Optical Satellite Data with Integrated Sensor Model Improvement

The geometric processing of remotely sensed image data is one of the key issues in data interpretation, added value product generation, and multi-source data integration. Although optical satellite data can be orthorectified without the use of Ground Control Points (GCP) to absolute geometric accuracies of some meters up to several hundred meters depending on the satellite mission, there is still a need to improve the geometric accuracy by using GCP. The manual measurement of GCP is time consuming work, and leads, especially for larger data sets with hundreds of satellite images, to a cost and time ineffective workload. To overcome these shortcomings, an autonomous processing chain to georeference and orthorectify optical satellite data is proposed which uses reference data and digital elevation models to generate GCP and to improve sensor model parameters (namely for rigorous and universal sensor models) for a series of optical Earth observation satellite systems. Using a restrictive blunder removal strategy, the proposed procedure leads to high quality orthorectified products or at least to a geometrically consistent data set in terms of relative accuracy. The geometric processing chain is validated using SPOT-4 HRVIR, SPOT-5 HRG, IRS-P6 LISS III, and ALOS AVNIR-2 optical sensor data, for which a huge amount of satellite data (3,200 scenes) has been processed. Relative and absolute geometric accuracies of approximately half the pixel size (linear Root Mean Square Error) are achieved.

InSAR and DEM quality monitoring of TanDEM-X

TanDEM-X is an interferometric SAR (InSAR) mission acquiring bistatic images with two satellites. Systematic mapping of the Earths land masses will provide individual interferometric data sets which will be mosaicked and calibrated into a global Digital Elevation Model (DEM). The concept of InSAR and DEM quality monitoring throughout the acquisition and processing phase is presented in this paper.

TerraSAR-X Staring Spotlight Mode Optimization and Global Performance Predictions

For the TerraSAR-X mission, a new staring spotlight mode has been implemented delivering very high azimuth resolution. Detailed performance analyses have been conducted to optimize the commanding parameters for this mode. Compared to the previously available TerraSAR-X imaging modes, staring spotlight requires operating the instrument with minimum margins and at the edge of the specifications, the radar has been designed for. Therefore, an additional step-a global acquisition simulation and analysis-is introduced during the operationalization to ensure the suitability of the derived commanding parameters on a global scale. This paper gives an overview of SAR performance analyses conducted for the mode optimization and implementation phases and presents a novel global performance assessment approach, which is generally applicable for the verification of operational SAR modes. Additionally, measurement results and exemplary acquisitions are shown.

Characteristics of TanDEM-X experimental modes

TanDEM-X is a spaceborne mission consisting in two satellites that are operated simultaneously for bistatic SAR acquisitions. The main objective of the mission is the systematic acquisition of a global and homogeneous digital elevation model (DEM) in bistatic stripmap mode. The close formation of the satellites makes the system very flexible and allows the commanding of a diversity of challenging experimental modes as bistatic spotlight or alternating bistatic stripmap modes. This paper gives an overview of the TanDEM-X experimental modes, focused on the analysis of already executed scientific orders, giving an overview of the different possibilities in commanding and image acquisition geometries. Also a first image characterization of the modes is included, in terms of image quality assessment and performance compliance.

First interferometric performance analysis of full polarimetric TanDEM-X acquisitions in the pursuit monostatic phase

TanDEM-X is a spaceborne mission consisting in two satellites that are operated simultaneously for bistatic SAR acquisitions. The flexibility offered by both SAR instruments allows the acquisition of full polarimetric data by activating the experimental dual-receive antenna (DRA) mode. For the first time on the TanDEM-X mission, it is possible to systematically command quad polarization acquisitions. We have estimated the quality of such full polarimetric products by a first interferometric performance analysis. The influence of different instrument parameters on the interferometric performance, such as chirp bandwidth or block adaptive quantization, have been investigated. In this paper first results are presented and recommendations for the optimization of the TanDEM-X quad polarization products are given.

Building Outline Extraction Using a Heuristic Approach Based on Generalization of Line Segments

Efficient and fully automatic building outline extraction and simplification methods are highly demanded for three-dimensional model reconstruction tasks. In spite of the efforts put into developing such methods, the results of the recently proposed methods are still not satisfactory, especially for satellite images, due to object complexities and the presence of noise. Dealing with this problem, in this article, we propose a new approach that detects rough building boundaries (building mask) from Digital Surface Model data and then refines the resulting mask by classifying the geometrical features of the high spatial resolution panchromatic satellite image. The refined mask represents finer details of the building outlines, which are close to the original building edges. These outlines are then simplified through a parameterization phase wherein a tracing algorithm detects the building boundary points from the refined masks and a set of line segments is fitted to them. After that, for each building, the existing main orientations are determined based on the length and arc lengths of the buildings line segments. Our method is able to determine the multiple main orientations of complex buildings. Through a regularization process, the line segments are then aligned and adjusted according to the buildings main orientations. Finally, the adjusted line segments are intersected and connected to each other in order to form a polygon representing the buildings outlines. Experimental results demonstrate that the computed building outlines are highly accurate and simple, even for large and complex buildings with inner yards.

Repeat-pass interferometric experiments with the Tandem-X constellation for accurate along-track motion estimation

This contribution presents two experiments performed with the TerraSAR-X (TSX) and TanDEM-X (TDX) satellites working in the pursuit monostatic configuration. Their objective is to estimate the along-track component of the motion in the scene in repeat-pass scenarios with an accuracy better than the one given by the stripmap azimuth resolution. Such performance is possible by exploiting the angular diversity of the bidirectional (BiDi) SAR mode and the π-shifted (or staggered) TOPS.

TanDEM-X going for the DEM: Acquisition, performance, and further activities

TanDEM-X is an innovative spaceborne X-band SAR mission designed to derive a digital elevation model (DEM) of the Earths land surface with an unprecedented relative vertical accuracy of 2m at a 12m posting. The global DEM is derived from interferometric SAR acquisitions performed by two radar satellites flying in close orbit formation, with adjustable baselines in cross- and in along-track directions. This paper provides an overview of the present mission status in terms of acquisition strategy and a quality summary of the currently available parts of the TanDEM-X global DEM in terms of absolute and relative height accuracy.

Orthorectification and DSM generation with ALOS-Prism data in urban areas

In this paper different methods for deriving digital surface models (DSM) from ALOS Prism three line stereo images are generated and analyzed. The methods used are classical hierarchical stereo matching with forward intersection and two different dense stereo methods. These are digital line warping which was derived from speech recognition algorithms and semi global matching which is originating in computer vision. All these dense stereo methods need epipolar imagery as input and provide so called disparity images as output. For this in a first step the Prism images has to be transformed by pairs to epipolar geometry. For the reprojection of the disparity images to real DSMs rational polynomial coefficients - which were computed from the satellite ephemeris and attitude date - are used. Finally the DSMs generated by all these different methods are compared to a DSM derived from an Ikonos stereo image pair with a ground sampling distance of 1 m.

Wrapped Staring Spotlight SAR

This paper proposes the wrapped staring spotlight (WSS) SAR imaging mode, which is a new method to extend the azimuth steering capability for phased array SAR to achieve either an improved azimuth geometric or radiometric resolution. It investigates the utility of steering directions with main lobe gains that are smaller than that of the grating lobes and exposes how these directions can be exploited. Furthermore, two methods are proposed to reduce the speckle and the image noise at once, i.e., the Look-Normalized Pattern Correction and the Ω-weighting. Based on two example TerraSAR-X WSS acquisitions, the image performance of extended and point targets is discussed.