Effect of Digital Elevation Model resolution on topographic correction of airborne SAR

Abstract

Topography in high relief mountainous areas may mask the signal variation in airborne Synthetic Aperture Radar (SAR) data caused by soil moisture, surface roughness and vegetation. It also a ects the quality of image calibration and registration. Good quality calibration and registration are required for the use of SAR in the estimation of soil water. To address the problem of topographic e ects, the widely available standard 30 m Ö 30 m United States Geological Survey (USGS) Digital Elevation Model ( DEM ) has been incorporated into SAR calibration and registration programs. The topographic resolution of SAR imagery relative to the USGS DEM was examined by comparing the correlation between incident angle (h) and SAR backscatter (s 0 ) in a high resolution DEM (mapped at 1 5 4800 and 1 5 600 from aerial photography for two small areas) to that in the USGS DEM (mapped at 1 5 24 000). We found that SAR resolved topographic features not resolved by the USGS DEM. Filtering and aggregation techniques were applied to reduce speckle, the apparent noise due to small topographic features resolved by SAR but not resolved by the USGS DEM, and the registration error. Increasing the ® lter window from 3Ö 3 to 5Ö 5 to 9 Ö 9 and the cell size from 6 m Ö 12 m to 30 mÖ 30 m to 90 mÖ 90 m, reduced the unexplained variability in backscatter by 50%. However, there was considerable unexplained variability at all levels of ® ltering and aggregation. Aggregation to 90 mÖ 90 m cell size resulted in blurred or obscured surface features of hydrological interest. Filtering with a 9Ö 9 window and resolution cell size of 30 m Ö 30 m was found to be optimal in terms of the amount of variability explained and the kinds of landscape features retained. Even after applying ® ltering and aggregation techniques, the correlation between s 0 and h for the high resolution DEM (r= 0.54) was much better than for the USGS DEM (r=0.36). Correction functions for the numerical estimation of terrain in¯uence on the backscatter variation in the SAR image were derived using empirical imaging models. Topographic e ects on s 0 were further reduced in the corrected images. However, even after correction there was considerable unexplained s 0 variability, some of which could be attributed to major topographic features. Thus, landscape features other than h need to be incorporated in topographic correction procedures.

Performance evaluation of different DEMs for topographic correction on LAPAN-A3: preliminary results

“…AW3D30 is a global Digital Surface Model (DSM) with 30 meters spatial resolution and first released on March 2017 25,28-30 . 9,10,31,32 Previously explained that it is appropriate to use a DEM with a similar grid size as the spatial resolution of the analyzed imagery. In this initial study, three types of DEM with different spatial resolution were analyzed based on their original resolution without prior resampling.…”

The effects of DEM resolution and neighborhood size on digital soil survey

“…Many studies have shown the effect of DEM resolution on the spatial pattern of terrain attributes (Chang and Tsai, 1991;Wolock and Price, 1994;Zhang and Montgomery, 1994;Gao, 1997;Goyal et al, 1998;Chaplot et al, 2000;Schoorl et al, 2000;Wilson et al, 2000;Thompson et al, 2001;McMaster, 2002). Zhang and Montgomery (1994) used DEM of different resolutions in conjunction with the D8 flow algorithm to detect patterns in storm runoff and surface saturation.…”

Soil-landscape modeling and land suitability evaluation: the case of rainwater harvesting in a dry rangeland environment

“…The digital elevation model was used to derive a grid of slope steepness. A 5 × 5 average (smoothing) filter was applied to clean the slope layer from small (suspicious) units (Goyal et al, 1998). The new output grid was converted to polygons to define the slope units.…”