Showing papers by "Peter Reinartz published in 2005"

DEM Generation from Very High Resolution Stereo Satellite Data in Urban Areas Using Dynamic Programming

Abstract: This article shows first results of implementing a method for creating DEMs from high resolution satellite imagery based on dynamic programming. The herein described DTW algorithm maps epipolar stereo image pairs line by line on top of each other using a method similar to dynamic time warping which is a common approach in speech recognition. The DTW algorithm is described and applied to several test images. The resulting DEMs and pros and cons of this method are shown and discussed.

Evaluation of spaceborne and airborne line scanner images using a generic ortho image processor

Abstract: One of the main processing steps of evaluating remote sensing data is the production of ortho images from the acquired raw scanner data. Since in most applications of thematic analysis, a rectified data set is required, there is a need for an effective – regarding time and accuracy - and generic – regarding different sensor systems – processor for performing this rectification for any desired sensor imagery. This is especially true when using the image data in Geographic Information Systems (GIS) and for data fusion and analysis with data from different sources or seasons. The accuracy of this rectification result is crucial for overlaying the data with existing data sets or maps and using them for evaluations like change detection, map updating a.o.. Triggered by the demand of an automatic processor embedded in the Data Information and Management System DIMS of DLR a generic ortho image tool was developed. The generic ortho image processor supports the production of ortho images from airborne and spaceborne digital line scanner images, as well as images from frame cameras. It is based on the Direct Georeferencing model using measurements of the exterior orientation of the sensor platform or sensor itself, the interior orientation (sensor parameters) and a digital elevation model. For the interior orientation models for pushbroom, whiskbroom and frame cameras as well as sensor calibration tables are supported. For the exterior orientation local level co-ordinate frames (navigation frame, orbital frame), earth centred earth fixed (ECEF) co-ordinate frames and generic mapping frames are supported. An approximate processing in a map projection is provided for airborne scanner data. The boresight misalignment matrix and the lever arm values are part of the functional model. Map projections are included in the processor. It also includes a link to the atmospheric correction processor ATCOR, which is also part of the automatic processing chain within DIMS. The ortho image processor is applied for different sensors like the spaceborne line scanners SPOT5 and Quickbird, and the airborne line scanners HyMap, ROSIS, DAIS and Daedalus. For the calibration of the boresight misalignment angles or attitude offset angles ground control information is used. The accuracy of the ortho images with and without ground control information is shown. For SPOT5 images with an absolute location accuracy of 1 to 2 pixels using only the metadata delivered by the image provider, few ground control points (about 2-4) are sufficient to reach horizontal accuracy in the sub-pixel range. For Quickbird a comparison example between ortho images produced with RPC (Rational Polynomial Coefficients) and DG (Direct Georeferencing) is shown. A series of ground control points at the airport base DLR Oberpfaffenhofen and surrounding area serves as geometric calibration field for the determination of the boresight misalignment angles of the airborne scanners, which are used within different flight campaigns. The achieved accuracy for the geometric calibrated airborne systems is demonstrated.

Comparison and fusion of DEM derived from SPOT-5 HRS and SRTM data and estimation of forest heights

Abstract: There are several ways to produce digital elevation models (DEM) from space- borne satellite data. In this study, two techniques and their results will be compared: DEM derivation with optical stereo data acquired with the French SPOT-5 HRS instrument and DEM derived from C-band and X-band radar data acquired during the SRTM mission. A comparison of the accuracy is given for different landscapes and land use classes using reference DEM from laser scanner data and aerial photography. Both systems show advantages and disadvantages but have similar accuracy values in comparison to a reference DEM, in both cases the resulting DEM is actually a mixture of a digital surface model (DSM) and a digital terrain model (DTM) since the reflection/back scatter results from a mixture of different targets in each resolution cell. Therefore in a forest area neither the forest canopy nor the terrain height itself is modeled. Additionally a DEM fusion, utilizing height error maps for each DEM, is performed. It is shown that a fusion of the DEM derived from optical and radar data leads to higher accuracies in nearly all cases. A comparison of the space borne DEM with the reference DEM shows a higher absolute difference in forest areas than in agricultural regions. The absolute difference gives an estimation of the canopy height of the trees, although the scattering process (in the radar case) and the reflection and matching techniques (in the optical case) cause lower values than the real height of the trees. It is shown whether an estimation of the real mean tree height is possible with the additional knowledge of tree parameters like species and density. Results are compared for both DEM generation techniques to the data received from in-situ measurements.

Multitemporal and Multispectral Remote Sensing Approach for Flood Detection in the Elbe-Mulde Region 2002

Abstract: The extreme flood event of the Elbe and Mulde Rivers in August 2002 caused, with its very sharp rise and decline of the water masses, a manifold of damage to the infrastructure as well as toxic deposits in the flooded areas. The paper gives a summary of the processing of multitemporal and multisensor remote sensing data for the purpose of monitoring this event. Methods and results for several thematic questions are presented and discussed. Procedures for the detection of flooded areas with operational satellite data (Landsat-ETM, IRS) are investigated. Further studies are performed regarding the classification of moisture classes in the flood plain in relation to the high water changes, the accumulation of sediments and silts for different land use classes and the erosive impact of the flood by using data with high spatial resolution from satellite (IKONOS) and from aircraft (Daedalus-Scanner). The time series of multispectral scanner data are very well suited for the spatial analysis of the damage and ecological risk, caused by the flood. The results correlate well with the data from in-situ measurements. At the same time they show how the gathering of samples can be optimized by using remote sensing data. The results can be directly integrated in existing GIS of the public authorities for the assessment and management of extreme flood events.

DSM and Orthoimages from QuickBird and Ikonos Data using Rational Polynomial Functions

Abstract: The rigorous approach for the derivation of digital surface models (DSM) and orthoimages from satellite and airborne scanner imagery via full modelling of the imaging process requires the knowledge of exterior and interior orientation of the camera. For IKONOS and QuickBird this basic data is not (fully) available to the user. Instead, rational polynomial functions (RPF) in standard form are provided as a substitute for describing the relationship between image and object space. To be able to derive DSM and orthoimages for this type of data even in the absence of appropriate ground control, software based on RPF has been developed. The software allows a lot of datums and projections for input and output data. This is important for worldwide application e.g. in case of catastrophes. The paper shows that a RPF is very near to linear in the object space variables longitude, latitude and height. This explains a large convergence radius and a rapid convergence in case of forward intersection. Residuals in image space from forward intersection are small and nearly constant in case of the GEO IKONOS-2 images tested. Large (also nearly constant) residuals in case of the QuickBird stereo pair can be used for a relative correction of the RPF either using residuals from verticality constraints with manually measured top/foot tie point pairs of large buildings or from forward intersection of a set of excellent tie points from matching. These corrected RPF can then be used to create a self-consistent set of DSM and orthoimages. The DSM derived from the high resolution data via RPF processing have been compared to best DSM available which was in most cases a C-Band SRTM model. Estimated mapping accuracy was found to correspond with the promises of the image provider in the case of available ground control.

Radar signatures of road vehicles: airborne SAR experiments

Abstract: The German radar satellite TerraSAR-X is a high resolution, dual receive antenna SAR satellite, which will be launched in spring 2006. Since it will have the capability to measure the velocity of moving targets, the acquired interferometric data can be useful for traffic monitoring applications on a global scale. DLR has started already the development of an automatic and operational processing system which will detect cars, measure their speed and assign them to a road. Statistical approaches are used to derive the vehicle detection algorithm, which require the knowledge of the radar signatures of vehicles, especially under consideration of the geometry of the radar look direction and the vehicle orientation. Simulation of radar signatures is a very difficult task due to the lack of realistic models of vehicles. In this paper the radar signatures of the parking cars are presented. They are estimated experimentally from airborne E-SAR X-band data, which have been collected during flight campaigns in 2003-2005. Several test cars of the same type placed in carefully selected orientation angles and several over-flights with different heading angles made it possible to cover the whole range of aspect angles from 0° to 180°. The large synthetic aperture length or beam width angle of 7° can be divided into several looks. Thus processing of each look separately allows to increase the angle resolution. Such a radar signature profile of one type of vehicle over the whole range of aspect angles in fine resolution can be used further for the verification of simulation studies and for the performance prediction for traffic monitoring with TerraSAR-X.

Results from an airborne SAR GMTI experiment supporting TerraSAR-X traffic processor development

Abstract: The launch of the advanced high resolution radar satellite TerraSAR-X in summer 2006 opens new possibilities for the demonstration of traffic monitoring from space. DLR is currently developing an operational traffic processor for the TerraSAR-X ground segment. The paper presents results from an airborne SAR GMTI campaign that was part of a study for algorithm development and processor design. DLR’s E-SAR sensor was used in an Along-Track Interferometry (ATI) mode to image vehicles in controlled and uncontrolled situations. The paper gives an overview on the experiment and presents the results of across- and along-track velocity estimation. Adapted SAR processing techniques were applied to enhance the peak energy of the moving objects in the focused SAR images. The paper presents first results and discusses the techniques.

DSM Generation from High Resolution Satellite Imagery Using Additional Information Contained in Existing DSM

Abstract: Information about the shape of the Earth's surface are required for several tasks like the creation of orthoimages or flood control. The generation of digital elevation models (DEM) with stereo images from space, or with interferometric synthetic aperture radar (InSAR) have been proven to be reliable and cost effective for larger regions, especially in remote areas and developing countries. Instead of a DEM, a digital surface model (DSM) is generated with remote sensing methods. Optical stereo image pairs are matched to get a large number of automatically located conjugate points. These points are mapped by forward intersection into the object space. The DSM is retrieved from these points by triangulation and interpolation. This method is mainly used to generate DSM from scratch. Thereby, the matching of optical images results often in areas without matching points, e.g. due to low contrast. This paper follows the approach to include the information of existing InSAR DSM into the point data set before or during the DSM generation from optical stereo images. Several methods are discussed and a SPOT image pair is analysed. Comparisons are shown for two inter¬po¬lations with and without additional input. Advantages of using the single data sets and of the combined data sets are discussed.

Experience and Perspective of Providing Satellite Based Crisis Information, Emergency Mapping & Disaster Monitoring Information to Decision Makers and Relief Workers

Abstract: Recognizing an increasing demand for up-to-date and precise information on disaster and crisis situations the German Remote Sensing Data Center (DFD) of DLR has set up a dedicated interface for linking the available and comprehensive remote sensing and analysis capacities with national and international civil protection, humanitarian relief actors and political decision makers. This so called “Center for Satellite Based Crisis Information” (ZKI) is engaged in the acquisition, analysis and provision of satellite based information products on natural disasters, humanitarian crisis situation, and civil security. Besides response and assessment activities, DFDZKI also focuses on the provision of geoinformation for medium term rehabilitation, reconstruction and prevention activities. DFD-ZKI operates in national, European and international contexts, closely networking with public authorities (civil security), non-governmental organizations (humanitarian relief organizations), satellite operators and other space agencies. ZKI supports the “International Charter on Space and Major Disasters”, which is a major cooperative activity among international space agencies in the context of natural and man-made disasters.

Estimation of along-track velocity of road vehicles in SAR data

Abstract: At the German Aerospace Center, DLR, an automatic and operational traffic processor for the TerraSAR-X ground segment is currently under development. The processor comprises the detection of moving objects on ground, their correct assignment to the road network, and the estimation of their velocities. Since traffic flow parameters are required for describing dynamics and efficiency of transportation, the estimation of the velocity of detected ground moving vehicles is an important task in traffic research science. In this paper we show for TerraSAR-X simulated data how the along-track velocity component of a moving vehicle can be derived indirectly by processing SAR data with varying frequency modulation (FM) rates and exploiting the specific behavior of the vehicle's signal through the FM rate space. An airborne ATI-SAR campaign with DLR's ESAR sensor has been conducted in April 2004 in order to investigate the different effects of ground moving objects on SAR data and to acquire a data basis for algorithm development and validation. Several test cars equipped with GPS sensors as well as vehicles of opportunity on motorways with unknown velocities were imaged with the radar under different conditions. To acquire reference data of superior quality, all vehicles were simultaneously imaged by an optical sensor on the same aircraft allowing their velocity estimation from sequences of images. The paper concentrates on the estimation of along-track velocities of moving vehicles from SAR data. Velocity measurements of vehicles in controlled experiments are presented, including data processing, comparison with GPS and optical reference data and error analysis.

DEM generation from very high resolution stereo data in urban areas

Abstract: In this article an attempt for improving an existing method creating DEMs fully automatically from stereoscopic image pairs is presented. Results applying this method to very high resolution (VHR) satellite imagery is shown. The herein discussed "column" algorithm is illustrated in brief and compared to a conventional algorithm frequently used in generating DEMs from satellite line scanner data. The presented algorithm is producing DEMs with an improved matching of steep objects as can be found in urban satellite imagery but introduces also some blunders in the generated DEMs.

The TerraSAR-X Traffic Monitoring System

Abstract: The presentation gives an overview about the TerraSAR-X traffic monitoring project at DLR. The tasks of the "traffic processor" and the overall ground segment are described. Results from first airborne campaigns are presented including the monitoring of a traffic jam on a motorway near Munich / Germany. Furthermore radar cross sections of passenger cars are presented.