Calibration and validation of the Shuttle Radar Topography Mission height data for southeastern Michigan

The Shuttle Radar Topography Mission (SRTM) provided data for detailed topographical maps of about 80% of the Earth's surface. SRTM consisted of single-pass C-and X-band interferometric synthetic aperture radars (INSARs). In order to apply SRTM data to remote sensing applications the data must be calibrated and validated. This paper presents the University of Michigan's SRTM calibration and validation campaign and our results using recently acquired C-band SRTM data of our calibration sites. A calibration array was deployed with the intention of determining the accuracy of INSAR-derived digital elevation maps. The array spanned one of the X-band swaths and stretched from Toledo, Ohio to Lansing, Michigan. Passive and active targets were used. The passive targets included trihedrals and tophats. The locations in latitude, longitude, and elevation of the point targets were determined using differential GPS. The data used in this study are "Principal Investigator Processor" data, which are not the refined final data product. However, we found the data to be of high quality. We report a 6 m to 12 m vertical height offset with a pronounced tilting trend. The average absolute offset is 9 m with a standard deviation of 2 m. This absolute height error is within the stated mission goal of 16 m, even before the final processing to refine the data. In order to calibrate the data, we remove the height offset and find that the resulting absolute height errors are at most 4.2 m in magnitude, with a standard deviation of 1.5 m.