X-SAR/SRTM Digital Height Models: Processing Status And Results

Abstract

The Shuttle Radar Topography Mission in February 2000 had two ‘single pass’ interferometric radar systems on board which are the C-band system of NASA/JPL and the X-band system from DLR. Both systems have been operated simultaneously during the mission. Independent processors have been developed to produce the digital terrain models. During SRTM the two C- and X-band radar systems of SIR-C/X-SAR were used as active ilumination sources and were supplemented by two passive antennas mounted on the top of a 60 m long boom. Due to this re-use of existing hardware the X-band system covered only a 50 km wide swath providing a net of elevation data during this 11day mission. After a difficult and long calibration phase in which mainly the baseline determination errors had to be removed we began the operational processing of the X-band data in December 2001. The processing sequence is continent-by-continent starting from the ocean, which is used as a reference. Each swath crossing as well as overlaps between adjacent swaths is used to support the height fixation and to check the height and location accuracy. Meanwhile the west part of Europe (30 deg longitude) is processed, Africa and South America have been finished and the digital height models and radar images are available to the public. Height error maps accompany the digital terrain models in tiles with a size of 15 arc-minutes. More than 1000 products have been delivered so far to the principal investigators, customers and to DLR’s own research team. The interferometric processing of the whole raw data set with an amount of 3600 Gbyte is already completed and the data are ready for the geocoding and mosaicking process. There are some problematic areas where the phase unwrapping failed which have now to be reworked with different procedures and matched parameters. In this paper we present the status of the processing and the future schedule as well as some results from comparison with reference DEM’s. The performance of the X-band data set is very good and is compliant with the specification. We discuss the applied filters, the height and location accuracy of the products, and we report about the experience and some interesting observations we made during the processing of 60 Million square kilometres of land surface. Several international principal investigators of X-SAR/SRTM have already analysed and compared the data products and have used the data set for geophysical investigations.