Advanced analysis of differences between C and X bands using SRTM data for mountainous topography

Abstract

By Interferometric Synthectic Aperture Radar (InSAR), during the Shuttle Radar Topography Mission (SRTM) height models have been generated, covering the earth surface from 56° south to 60.25°n orth. With the exception of small gaps in steep parts, dry sand deserts and water surfaces, the free available US C-band data cover the earth surface from 56°s outh to 60.25° north completely while the X-band data, distributed by the DLR (German Aerospace Center), cover it only partially. The C-band and Xband radar cannot penetrate the vegetation because of the short wavelength. Therefore, the height Keywords SRTM (Shuttle Radar Topography Mission) . InSAR (Interferometric Synthetic Aperture Radar) . DSM (Digital Surface Model) . DEM (Digital Elevation Model) . Accuracy models are not Digital Elevation Models (DEM) representing bare Earth surface without any details, they are Digital Surface Models (DSM) representing the visible surface including vegetation and buildings. In the area of Zonguldak, Turkey, C-band and X-band DSMs are available and have been analysed in cooperation between Zonguldak Karaelmas University (ZKU) and Leibniz University of Hannover. The digitized contour lines from the 1:25,000 scale topographic maps and also a more precise height model derived directly from large scale photogrammetric mapping are used as reference height models.The terrain inclination influences the accuracy strongly, but also the directions of the inclination in relation to the radar view direction, the aspects, are important. Independent from the aspects, the analysed results do have root mean square differences against the reference data fitting very well to the Koppe formula SZ=a+b*tan α. The analyses are made separately for open and forest areas, with clear 336 J. Indian Soc. Remote Sens. (September 2009) 37:335-349 accuracy differences between both. Also, the analysis of X-band separately for three sub-areas is done and the positive effect of double observation to the accuracy has been clearly determined. The C-band data are only available with a spacing of 3 arcsec, corresponding to 92m × 70m, while the X-band data do have a spacing of 1 arcsec. This is important for the interpolation in the mountainous test area. The accuracy of the height points is approximately the same for the C-and the X-band data. But the C-band data which have three times larger spacing than Xband data, do not include the same morphological information. While C-band data contain very generalised contour lines X-band data have quite more details depending on 1 arcsec point spacing. The differential DEMs have been generated, separately, for displaying the differences between SRTM height models and reference DEMs of the test field.

Assessment of the Accuracy of SRTM C- and X-Band High Mountain Elevation Data: a Case Study of the Polish Tatra Mountains

“…To date, assessments of the accuracy of SRTM DEMs in mountainous areas have been applied mainly in the context of glacier monitoring (KÄ Ä B 2005;BERTHIER et al 2006;SURAZAKOV and AIZEN 2006;FUJITA et al 2008;FREY and PAUL 2012), hydrological modelling (LUDWIG and SCHNEIDER 2006) and terrain morphometry (GOROKHOVICH and VOUSTIANIOUK 2006;SEFERCIK and ALKAN 2009). However, complex investigations of the factors that can potentially influence the accuracy of SRTM DEMs in mountainous areas, especially for the recently released X-band data, are lacking.…”

Analysis of the accuracy of Shuttle Radar Topography Mission (SRTM) height models using International Global Navigation Satellite System Service (IGS) Network

“…The SRTM data is freely available in two bands, X and C, at resolutions of 30 and 90 m, and have been used extensively by scientific researchers worldwide in different disciplines. Ever since the release of SRTM data in 2000, many studies have evaluated the quality of this data and all have found it to comply with the SRTM mission goal of 16 m linear error at 90% confidence equivalent to RMSE of ∼ 10 m. Global validation of X-band data has not been carried out although some local studies have validated the X-band data (e.g., Turkey (Sefercik and Alkan 2009) and Poland (Kolecka and Kozak 2013)) and observed that the accuracy of the Xband data was in the same range as C-band SRTM and the latter was marginally more accurate. However, these studies did not use GPS data to test the accuracy of the X-band SRTM data.…”

Contribution of Normalized DSM to Automatic Building Extraction from HR Mono Optical Satellite Imagery

“…As known, the main parameter for most realistic DSM and DTM generation using optical stereoscopy is the number of proper matching and height points that are marked by the operator. The heights of the entire included points in requested grid interval of a DSM or a DTM are automatically calculated by interpolation which decreases the vertical accuracies of them [Passini and Jacobsen, 2007;Sefercik and Alkan, 2009]. The most significant factor that minimizes the negative influence of interpolation is measured point density for the generation area.…”