Comparison of The Accuracy of Morphometry And Stream Patterns Extracted From ASTER Digital Elevation Model (DEM) And Topographic Maps (Case Study: Oshtorankooh)

This study aims to evaluate the quality and accuracy of the DEMs extracted from ASTER and topographic data of 1:25000 for morphometric analysis of stream patterns in different formations.
Matherials and To examine the DEM, first the map of drainage network of the studied area was prepared based on ASTER DEM and topographic map in Arc hydro medium.
In the next step, the Raster drainage network of the area was calculated in 30 thresholds values for the whole catchment area. Discussion and The results imply from the morphometry perspective the stream patterns extracted from ASTER and topography in all the formations are similar but different in number of stream patterns.
Although absolute accuracy of the topography DEM seems to be low, compared to the DEM data obtained from ArcGIS it is more valuable.
Also, the raster layers are not a reliable and precise source for comparison of the results obtained from the two extraction methods of stream patterns. In case of conversion to vector layers, the results will be clearer and more obvious.
The computer algorithms are not suitable and accurate sources for determination of the length and number of stream patterns. The reason lies in this fact that in the regions with a steep slope, there are many errors in estimation of the length of Grade 1 stream patterns when using manual layers and the precision is poor.
In contrary, in low slope regions the computer algorithms are unable to analyze the length of river and in mild slope regions this ability is improved.
Owing to the mountainous nature of the region, the results obtained from the Aster DEM are less accurate than those obtained from the topographic maps.
In addition, the Ilam-Sarvak formation (made of limestone with black shale limestone) with drainage density of 52.35, has the highest number of stream patterns versus other formations (Table 1).
The width of the grade 1 stream patterns in this formation, due to the higher amount of shale is larger than that in other formations and the RMSE magnitude of the Ilam-Sarvak formation is 192.82.
The Soormeh formation (made of limestone and dolomite limestone), containing the least number of stream patterns and the drainage density of 0.059, shows the lowest magnitude of RMSE (0.01). The morphometry obtained from ASTER DEM and topographic maps seems alike.
But, the results related to the number, length and drainage density of the stream patterns are discrepant. Furthermore, the results of RMSE in various formations (Table 5) verify their accuracy.
In mountainous regions, the accuracy of the number of stream patterns obtained from ASTER DEM is much lower than that obtained from topography.
The number of stream patterns depends on the material and slope of formations.
The results obtained from analysis show there is a direct correlation between drainage density and number of stream patterns and an indirect correlation between drainage density and RMSE.