dr. Naief Alrousan
"Automatic Extraction of streams from digital Elevation Model:
A Case Study in North Badia-Jordan"
A digital Elevation Model is simply digital map of elevation data, these data made up of equally sized gridded cells each of which with a unique elevation. There are many uses and application of DEMs such as engineering and scientific applications. The present study aims to evaluate the ability of extracting stream network using DEM extracted from SPOT satellite stereopaires. The data extracted from DEM were compared with stream network digitized from UTM and JTM 1:50000 scale topographic maps. The study area is located in North Badia consisting of 120 km2. for the stream networks of the study area greater attention was paid to deriving such networks automatically. However this raises the question of elevation models from which they are derived. DEM of the study area has been extracted from stereo model of SPOT images using EASI-PACE system. The thirty – four ground control points and 10 checkpoints have been used for geometric correction of the stereo model. Geometric accuracy test of RMSE of planimetry for the left image shows ± 24.00 m at the GCPS and ± 24.00 m at the check points. The validation accuracy test of the extracted gridded 20 m resolution DEM show an accuracy test of heights ± 3.11 m at the GCPs, and ± 4.78 m at the check points. From the EASI-PACE system a DWCON program have been used. This program is a conditioning procedure for drainage network analysis, and the DEM has been applied in this program to produce the following four data sets tha are required for subsequent drainage analysis: a digital elevation data set with depression filled, data set indicating the flow direction for each pixel, a flow accumulation data set in which each pixel receives a value equal the increase in the accumulation value in the flow direction. A drain program has been used to locate drainage networks.
A digitize drainage from 1:50000 scale Al- aretain topographic maps of the same area of UTM and JTM. The results of the superimposed drainage digitized from the topographic maps over the drainage extracted from the DEM show that DEM delineated streams are usually close to, but not coincide with mapped streams. Two main factors affected the disagreement. The first factor is related to the accuracy of the Dem. the second factor is affected by topography in which the pronounced topography showed agreement. The stream channels may be cut into surrounding terrain and the difference in elevation would poorly represented in the DEM.