Showing papers by "Peter Reinartz published in 2008"

Towards Automated DEM Generation from High Resolution Stereo Satellite Images

Abstract: High resolution stereo satellite imagery is well suited for the creation of digital surface models (DSM) In this paper, a system for highly automated DSM and orthoimage generation based on CARTOSAT-1 imagery is presented The proposed system processes photometrically corrected level-1 stereo scenes using the rational polynomial coefficients (RPC) universal sensor model The RPC are derived from orbit and attitude information and have a much lower accuracy than the ground resolution of approximately 25 m Ground control points are used to estimate affine RPC correction Accurate GCP are not always available, especially for remote areas and large scale reconstruction In this paper, GCP are automatically derived from lower resolution reference images (Landsat ETM+ Geocover and SRTM DSM) It is worthwhile to note that SRTM has a much higher lateral accuracy than the Landsat ETM+ mosaic, which limits the accuracy of both DSM and orthorectified images Thus, affine RPC correction parameters are estimated by aligning a preliminary DSM to the SRTM DSM, resulting in significantly improved geolocation of both DSM and orthoimages Robust stereo matching and outlier removal techniques and prior information such as cloud masks are used during this process DSM with a grid spacing of 10 m are generated for 9 CARTOSAT-1 scenes in Catalonia Checks against independent ground truth indicate a lateral error of 3-4 meters and a height accuracy of 4-5 meters Independently processed scenes align at subpixel level and are well suited for mosaicing

Detection of Traffic Congestion in Optical Remote Sensing Imagery

Abstract: A new approach for the traffic congestion detection in time series of optical digital camera images is proposed. It is well suited to derive various traffic parameters such as vehicle density, average vehicle velocity, beginning and end of congestion, length of congestion or for other traffic monitoring applications. The method is based on the vehicle detection on the road segment by change detection between two images with a short time lag, the usage of a priori information such as road data base, vehicle sizes and road parameters and a simple linear traffic model based on the spacing between vehicles. The estimated velocity profiles for experimental data acquired by airborne optical remote sensing sensor - 3 K camera system - coincide quite well with the reference measurements.

Generation of coarse 3D models of urban areas from high resolution stereo satellite images

Abstract: With the emergence of more and more satellites delivering very high resolution (VHR) imagery with ground sampling distances in the range of one meter or below the generation of three dimensional urban models directly from space may become possible. Such models are required for many applications in areas where no up-to-date detailed urban mapping exists like in developing countries. Besides the creation and updating of maps from sprawling urban settlements, such three dimensional models are also very useful for simulation and planning. For example simulations of catastrophic events like flooding, tsunamis or earth quakes rely on digital terrain models (DTM) populated with three- dimensional man made and natural objects. Using VHR satellite imagery is often the faster and cheaper alternative to acquiring aerial photos or even laser DEMs or in some times even the sole source of information for remote areas. In this paper a method for an automatic processing chain for urban modeling based on stereo images from VHR satellites is proposed. After import and preprocessing of the images a digital surface model (DSM) is derived from the stereo data. Subsequently a digital terrain model (DTM) and true ortho images are generated based on the DSM. Using a high objects mask and a vegetation mask based on the normalized difference vegetation index (NDVI) a coarse classification will be derived and suitable models for the detected objects (e.g. houses, trees, ...) are selected and finally the 3D models get exported in a suitable format like VRML.

Stereo Evaluation of ALOS/PRISM Data on ESA-AO Test Sites - First DLR Results

Abstract: DLR's Remote Sensing Technology Institute has more than 20 years of history in developing spaceborne stereo scanners (MEOSS, MOMS) and the corresponding stereo evaluation software systems. It takes part in the ESA/JAXA-AO Program to evaluate the performance and potential of the three-line stereo scanner PRISM (Panchromatic Remote-sensing Instrument for Stereo Mapping) and the multispectral imaging sensor AVNIR-2 onboard the Japanese satellite ALOS as a principal investigator. German (Southeast Bavaria) and Spanish (Catalonia) test sites are proposed for which also PI evaluations for the SPOT-5 HRS Scientific Assessment Program (SAP) had been done already in 2003/04, and for the Indian CARTOSAT-1 (C-SAP) from 2006 onwards. In this paper, the process of direct georeferencing according to JAXA is shown and first results are presented. Ground control points (GCPs) are used to estimate boresight angles to improve the accuracy of the direct georeferencing. Rational polynomial coefficients (RPCs) are generated using DLR software. The comparison of a GCP-based approach and the rigorous approach reveals an oscillation of the satellite in the order of up to one pixel on the ground. The oscillations can not be compensated by an RPC-based approach. DEMs are generated and the coregistration of forward, nadir and backward view is examined. Thereby, problems in the processing of the interior orientation are revealed.

Comparison of orthorectification methods suitable for rapid mapping using direct georeferencing and RPC for optical satellite data

Abstract: One of the first essential steps in response to a crisis event is to provide current, precise, and rapid information about the extent of the event, the affected population and infrastructure (e.g., information for relief teams). Experiences in crisis mapping show, that remote sensing data are an important information source to get an overview of the situation. For an efficient use of geo-information before or during a crisis of any kind, all information should be orthorectified. Satellite data are delivered normally geocoded with varying accuracy. However, today orthorectification without ground control points (GCP) using only ephemeris and attitude data measured on board the satellite provide an absolute accuracy of about 20 m to 1 km (depending on the satellite). For the intended applications like change detection this accuracy is not sufficient. For this purpose, accuracy in the sub-pixel range is necessary requiring a precise orthorectification. Different methods deployed in different software packages are analyzed and compared in this paper. They are chosen depending on the available metadata. To get an objective comparison of the different orthorectification methods, their accuracy is determined for several test datasets in this study. Additionally to the comparison of the accuracy, further criteria are analyzed like the potential of the algorithm for optimization and automation and the computing time needed, since the timely supply of information is also one of the most important requirements in crisis respond mapping. Results using the commercially available software packages Erdas Imagine, PCI Geomatics and ENVI are compared to products of the in-house developed software XDibias of the German Aerospace Center (DLR). All programs result in high accuracy. Differences are experienced in the computing times and userfriendlyness. While the commercial programs are very user friendly, knowledge about the details of the in-house developed software are very helpful and the automation potential of it has already been proven.

Application of generalized partial volume estimation for mutual information based registration of high resolution SAR and optical imagery

Abstract: Mutual information (MI) has proven its effectiveness for automated multimodal image registration for numerous remote sensing applications like image fusion. We analyze MI performance with respect to joint histogram bin size and the employed joint histogramming technique. The affect of generalized partial volume estimation (GPVE) utilizing B-spline kernels with different histogram bin sizes on MI performance has been thoroughly explored for registration of high resolution SAR (TerraSAR-X) and optical (IKONOS-2) satellite images. Our experiments highlight possibility of an inconsistent MI behavior with different joint histogram bin size which gets reduced with an increase in order of B-spline kernel employed in GPVE. In general, bin size reduction and/or increasing B-spline order have a smoothing affect on MI surfaces and even the lowest order B-spline with a suitable histogram bin size can achieve same pixel level accuracy as achieved by the higher order kernels more consistently.

GPU-based Orthorectification of Digital Airborne Camera Images in Real Time

Abstract: The usage of airborne camera systems for near real time applications will increase in the near future. This paper purposes a new hardware/software architecture to establish real time computation of images obtained from the DLR wide area airborne 3K-camera system. The main applications of our system are e.g. to monitor automotive traffic, to determine the workload of public road networks during mass events, or to obtain a survey of damages in disaster areas in real time. Therefore, many different image processing tasks have to be executed in real time. Orthorectification of images is necessary prior to all other processing tasks, e.g. before mapping data from street data bases into images or before tracking of vehicles. Nowadays, the calculation becomes possible due to fast graphic processing units (GPU) and with the support of a distributed real time system. In order to achieve real time image processing, we suggest a GPU-based algorithm for image orthorectification. The GPS/IMU-system provides the position and orientation of the aircraft with 128Hz quite accurately. Assuming synchronized measurements with the camera system and given camera calibration, direct orthorectification is implemented using OpenGL. Therewith, we are able to process high resolution images consisting of 16 MPixels with a frame rate of 3 Hz. This paper describes the implementation of the real time algorithm and gives first results.

Automatic Traffic Monitoring from an Airborne Wide Angle Camera System

Abstract: We present an automatic traffic monitoring approach using data of an airborne wide angle camera system. This camera, namely the “3K-Camera”, was recently developed at the German Aerospace Center (DLR). It has a coverage of 8 km perpendicular to the flight direction at a flight height of 3000 m with a resolution of 45 cm and is capable to take images at a frame rate of up to 3 fps. Based on georeferenced images obtained from this camera system, a near real-time processing chain containing road extraction, vehicle detection, and vehicle tracking was developed and tested. The road extraction algorithms handle a-priori information provided by a road database for a first guess of the location of the roads. Two different techniques can be used for road extraction. In the first method, roadside features are found by using an edge detector based on ISEF filtering, selecting the steepest edge, which is normally the edge between the tarry roads and the vegetation. The second method extracts roads by searching the roadside markings using a dynamical threshold operator and a line detector. Vehicle detection then is limited to the road areas found by the road extraction algorithms. It is based on an edge detector, a k-means clustering of the edges, and on geometrical constraints, e.g. vehicle size. Vehicle tracking is performed by matching detected vehicles in pairs of consecutive images. For this matching the normalized cross correlation is calculated for each detected car within a limited search area. The algorithms for road extraction, vehicle detection and vehicle tracking proved to be quite sophisticated, enabling car detection and tracking rates with a completeness of 70 % and a correctness of up to 90 % on images obtained from a flight height of 1000 m.

The Future Spaceborne Hyperspectral Imager EnMAP: Its Calibration, Validation, and Processing Chain

Abstract: The Applied Remote Sensing Cluster of the German Aerospace Center (DLR) is responsible for the establishment of the payload ground segment for the future German hyperspectral satellite mission EnMAP (Environmental Mapping and Analysis Program), which is planned to be launched in 2012. EnMAP covers the spectrum from 420 nm to 2450 nm with a spectral resolution of at least 10 nm and a spatial resolution of 30 m x 30 m with a swath width of 30 km. The primary goal of EnMAP is to quantify and analyze diagnostic parameters describing key processes on the Earth’s surface. To achieve high-quality and consistent data with respect to the same and other missions, extensive calibration and validation activities are foreseen during the five years of mission operations. The calibration results will be integrated in the processing chain to obtain standardized products, which include radiometric, geometric, and atmospheric correction. Here we focus on the following three aspects of the EnMAP mission: (a) analysis of data of the various calibration sources, (b) geometric processing with precise orbit and attitude data as well as atmospheric correction, and (c) supporting ground, airborne, and spaceborne campaigns to assess the quality of the output data delivered by the processing chain.

Stereo Evaluation of CARTOSAT-1 Data Summary of DLR Results During CARTOSAT-1 Scientific Assessment Program

Abstract: The Remote Sensing Technology Institute (IMF) of the German Aerospace Center (DLR) has more than 20 years of history in developing spaceborne stereo scanners and the corresponding stereo evaluation software systems. It takes part in the CARTOSAT-1 Scientific Assessment Program (C-SAP) as a principal investigator for German (Southeast Bavaria) and Spanish (Catalonia) test sites and as a Co-I for a French test site (Mausanne-les-Alpilles). A rich variety of landscapes is present in these three test sites. In all cases ground truth in form of GCP (or orthoimages of high resolution) and DTM/DSM (digital terrain or surface models) of sufficient accuracy have been delivered by the principal investigators.Rational polynomial functions (RPC) are provided by the distributing Indian agency (Space Applications Centre (SAC) of ISRO, Ahmedabad) as a universal sensor model for each scene. The inherent absolute orientation accuracy of the RPC models in the CARTOSAT-1 stereo imagery used here turned out to be around 100 m (normally). Thus, to exploit the high resolution of 2.5 m, RPC have to be corrected via the available ground truth. It is shown that the correction by an affine transformation is necessary in order to achieve sub-pixel accuracy in the stereo evaluation of full scenes. The remaining standard deviations of the residuals in image space during RPC correction are about 0.5-1 pixel in ground control points (GCP). Stereo evaluation is done by DLR processing software. Hierarchical intensity based matching and subsequent region growing are used to automatically derive a dense set of stereo tie points. An effective blunder reduction is based upon bi-directional LSM, quasi-epipolar reprojection of the tie points, and control of residuals in stereo forward intersection. Shifts between aft/fore orthoimages are found to be in sub-pixel range. DSM accuracy assessment is done via the statistics of height differences compiled by the forward intersection software. This is sufficient if accurate GCP for RPC correction are available. For direct comparison of the generated DSM with the reference DTM/DSM a 3D shift is estimated via least squares adjustment and mean and standard deviations of the DTM/DSM differences after shifting are provided. In summary, standard deviations of 2-4 m are achieved.

Gmes fast track land service 2006-2008 orthorectification of spot 4/5 and irs-p6 liss iii data

Abstract: The GMES (Global Monitoring for Environment and Security) Fast Track Land monitoring Service (FTLS) is a service to provide on a regular basis land cover and land use change datasets, which can be used by a wide range of downstream services at European, national, regional and local scale. Under ESA contract DLR (German Aerospace Center) produced two multi-temporal datasets of orthorectified images covering the participating EU27 and neighbouring countries (overall 38 countries). An operational and automatic processing chain to process about 3700 satellite images has been established including quality control and creation of a European wide consistent GCP database. The orthorectified products are derived from a mixture of high resolution satellite images from SPOT 4 with 20 m GSD, SPOT 5 with 10 m GSD and IRS-P6 LISS III with 23 m GSD, each with four spectral bands, and geometrically corrected towards European Map Projection with 25 m resolution and national map projection for each country with 20 m resolution using DLR's in-house developed versatile orthorectification S/W package. An overall geometric accuracy of about 10 m RMSE in each direction with respect to the European land cover dataset Image2000 (EU25) and USGS ETM+ land cover dataset (neighbouring countries) has been reached. The paper describes the background of the Image2006 project, the newly developed procedures and methodologies of the automatic and operational orthorectification chain including its limitations in problematic cases, as well as the results in terms of statistical evaluations.

Near Real Time Processing of DSM from Airborne Digital Camera System for Disaster Monitoring

Abstract: Knowledge of accurate digital surface models (DSMs) is a valuable information for security authorities and organizations during emergencies, disasters, or big events. In this context, the potential of the recently developed digital optical camera system (3K) to derive DSMs automatically and in near real time will be evaluated. The 3K camera system with a frame rate of 3Hz consists of three non-metric off-the-shelf cameras (Canon EOS 1Ds Mark II, 16 MPixel), which are aligned in an array with one camera looking in nadir direction and two in oblique direction. The DSMs are calculated using a subpixel hierarchical matching based on interest points followed by a region growing algorithm. Exterior orientation is given online by GPS/IMU data, whereas interior camera parameters are provided in advance. The resulting DSM is calculated by forward intersection. For the validation, the point accuracies in relation to the base-to-height ratio as well as the reached point density in relation to the calculation time were calculated. Two flight campaigns with the 3K camera system were performed with varying frame rates over the centre of Munich on 30th April and on 17th June 2007. Point accuracies over flat terrain were validated with reference DEMs and correspond quite well to simulated accuracies. The validation showed that smaller base-to-height ratios decrease the point accuracies but increase point densities as images are more similar in particular over urban areas. Exemplarily possible applications for near real time DSMs in the context of disaster monitoring are described, e.g. monitoring of land slides, 3D change detection over urban area, and monitoring of infrastructure. Problematic in all cases is the long processing time, thus the matching algorithms must be modified or new techniques must be applied. Some starting points for the reduction of processing times are discussed. In this context, the proposed matching algorithms and results serve as reference for much faster implementations.