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Pictures 2a and 2b perform ASTER DEM images are produced from ASTER stereo data, as well as 3D images of ASTER RGB 321 composites. ASTER DEM is generated from 3n and 3b stereo bands using 10 GCPs. ASTER DEM has 15 m spatial resolution, and the contour of DEM looks softer compare to contour of SRTM DEM that only has 90 m spatial resolution. Blue color shows the area with lower height (lower terrain). The gradation from blue to red color shows that the heights of land surface increase. Relative height obtained from ASTER DEM in the study area achieves to 752 meter. The 3D images in picture 2b show union result from DEM data and ASTER RGB 321 composite images, whereas the most of study area consists of mountain areas with dense vegetation coverage area, in the contrary the land that has lower height and less vegetation coverage area is located in certain small coastal area.  Picture 2 DEM ASTER and 3D image of ASTER RGB 321 composite  Picture 3 Comparison of height distribution of ASTER DEM and SRTM DEM along vertical and horizontal transect lines Evaluation to the accuracy of ASTER DEM is done by comparing height distribution along transect lines vertically and horizontally. Picture 3 shows vertical and horizontal transect lines in ASTER images, and comparison of height distribution between ASTER DEM and SRTM DEM along the transect line's track. Height distributions of the both DEM data are almost same along vertical and horizontal lines. On the other hand absolute values of height are not same, especially in the high topography areas such as mountain with dense vegetation coverage areas. Table 1 shows measurement results of ASTER DEM and SRTM DEM for whole images (full image). Minimum, maximum and mean values from ASTER DEM and SRTM DEM show relative same values, even though ASTER DEM has wider range values comparing to SRTM DEM. This result shows that ASTER DEM is more sensitive than SRTM DEM (It is related to spatial resolution of ASTER DEM higher than SRTM DEM). Negative values at ASTER DEM minimum values are pixel values located in the coastal water area, where some certain areas (such as: water and cloud area) will cause distortion to the generated DEM values.
The accuracy of generated ASTER DEM is analyzed by extracting the height difference between the both DEM images. Minimum and maximum values, mean error and mean absolute error values are calculated. Classification process of height differences between those both image is done to analyze percentage of coverage area for each height difference interval. Classification is done in land area only (water area is not included). Table 2 and 3 show measurement results of height difference between the both DEM images and coverage area percentage for each height difference interval. Measurement result shows that minimum and maximum height difference values are more than 100 m, meanwhile absolute mean error is up to 27 m (ASTER DEM value to SRTM DEM value). These results perform quite wide for error level, but it is not significant different compare to previous research's results. The previous research has reported that ASTER accuracy is up to 25 m for mountain areas with dense vegetation coverage (Richard Selby, PCI Geo). Classification result for 0-10 m of height difference is covering at 29% of land area, 11-20 m is at 23% and 21-30 meter is at 15%, therefore 0-30 meter for this field study is covering 67% of land area in whole DEM image. Meanwhile, 31-60 meter of height difference is at 12% and more than 60 meter is at 11% of land area. Obtaining results shows that the height difference between ASTER DEM and SRTM DEM data are quite big (the height difference more than 31 meter is up to 23% from the study area), but this difference can be less in certain ways, (to increase the accuracy of generated DEM) such are :
This paper describes DEM generation method from ASTER stereo image and evaluates the accuracy of generated ASTER Dem by analyzing height different between ASTER DEM and SRTM DEM. Several results are obtained below:
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