Bernd Rabus

SRTM-Mission - cross comparison of X and C band data properties

In February 2000 the Shuttle Radar Topography Mission (SRTM) mapped large areas of the global landmass using two radar systems operating simultaneously in X- and C-band. The radar mapping instrument consisted of modified versions of the SIR-C C-band and X-band radars flown on the shuttle in 1994. Modifications included a 60 m retractable: boom, with C-band and X-band receive-only antennas attached to the booms end. High accuracy metrology systems were added to measure the shuttle position and attitude, and the position of the boom antennas. The dual apertures at each band form radar interferometers suitable for making high accuracy topographic maps of the Earth. The C-band data set is being processed by JPL for the archives of the US National Imaging and Mapping Agency (NIMA) and the National Aeronautics and Space Administration (NASA). The X-band data set is processed and distributed at DLR Germany. This paper compares the specific properties of the X- and C-band data sets with respect to global coverage, height accuracy, sensor specific errors, product definition, product format and availability.

SRTM/X-SAR: products and processing facility

The Shuttle Radar Topography Mission SRTM mapped the Earths surface in two frequencies - C-band and X-band. This paper presents the SRTM/X-SAR products, the processing and archiving facility as well as the procedures on how the products will be made available. The raw data volume stored online within the robot archive of DLRs Remote Sensing Data Center (DM) will be about four TBytes. The processing of this amount of data requires the use of high performance parallel computers scheduled and supervised by a new control and information system. The DEM production line is split into three subsystems the scanning and screening, the SAR as well as interferometric processing and finally the elevation derivation and mosaicking procedure. An online catalogue accessible via web browser provides all information required for a product selection.

SRTM X-SAR calibration results

The paper presents the results of the Shuttle Radar Topography Mission (SRTM) X-band calibration at DLR as of April 2001, the time of writing. While some areas may be subject to further improvement, the overall image will not change significantly. We summarize the various calibration issues, the methods applied and the results obtained. Addressed topics are: Timing calibration, SNR and coherence, motion analysis and instrument phase errors. The qualitative and quantitative effects of the distortions above on the DEM quality are discussed.

GeMoS-a system for the geocoding and mosaicking of interferometric digital elevation models

The task of mapping and monitoring the Earths surface covers various application fields. Usually this 3-dimensional problem is split into a 2-dimensional planar description of the Earths surface in maps supplemented with the height information, stored as separate digital elevation models (DEMs). However there is a lack of suitable global height information. DLRs Remote Sensing Data Center (DFD) implemented a production chain for the operational generation of DEMs. It currently offers this service on the basis of SAR data from the ERS tandem missions. Starting in late 1999 it will be used for the processing of the X-band data of the Shuttle Radar Topography Mission (SRTM). The system will also be adapted for the generation of interferometric products delivered from the ASAR sensor of ESAs ERS follow on system ENVISAT. Part of the interferometric processing chain is the Geocoding and Mosaicking System (GeMoS). It enables the conversion of the unwrapped phase to height values, their geocoding into a variety of map projections, as well as the composition of individual InSAR DEMs to a large area, quality enhanced elevation product. An adjustment procedure improves the imaging parameters and as a consequence the product quality. The present paper briefly describes the system, its functionalities and the implemented approaches.

Analysis of SRTM interferometric X-band data: first results

During February 11/sup th/-22/sup nd/, 2000, the Shuttle Radar Topography Mission (SRTM) imaged the Earth with the first spaceborne single-pass SAR interferometer. The acquired data set will greatly enhance the knowledge of the global topography. At DLR the German Remote Sensing Data Center will process the X-band SAR data set to a nearly global homogenous digital elevation model (DEM). This work summarizes the first experiences with the SAR data.

Filtering of interferometric SRTM X-SAR data

In February 2000, the Shuttle Radar Topography Mission acquired a global digital elevation model (DEM) within only 11 days. During the years 2000 and 2001, extensive testing and calibration activities followed at DLR. One of the questions during that phase was, which kind of interferogram filtering should be performed. We analyzed different types of filters from the perspective of an operational DEM processing chain. Our paper describes the filters investigated and the arguments that finally led us to the decision to implement a relatively simple Gaussian smoothing in the time domain. This filter performed best in many disciplines and produced the smallest artifacts.

SRTM X-SAR DEM of Europe-Results and algorithmic improvements

In February 2000, the Shuttle Radar Topography Mission acquired a global digital elevation model (DEM) within only 11 days. During the years 2000 and 2001 extensive testing and calibration activities primarily based on ocean surface data took place at DLR. The calibration phase is now finished and the quality of the products analyzed so far met all specifications. The routine processing of the German X-band data at DLR began in November 2001, starting with Europe. Now, that hundreds of image frames over Europe are being processed and mosaicked to a continent-wide DEM, the largescale system stability becomes visible. Our paper reports the experiences from mosaicking based on self-consistency tests and on comparison with independent reference data. While the overall quality is promising, there are still some outliers to be investigated and compensated. The calibration concept based on the use of ocean data will be presented and discussed. Adaptations and improvements based on self-consistency will be presented, that allow a more robust and automated processing.