Vertical Accuracy Assessment for the Free Digital Elevation Models SRTM and ASTER in Various Sloping Areas.

The research applied ASPRS standards to determine the necessary number of check points to evaluate accuracy, with a proposed application of a simple method to identify outliers in elevation differences. Tests were conducted in the Latakia Governorate after dividing it into three areas: a moderate slope area, a moderate steep slope area, and a steep slope area. As for the check points, they were extracted from a topographic map with a scale of 1/25000.The results showed a strong positive correlation between reference elevations and elevations extracted from both the SRTM and ASTER models in all test areas, with a Pearson coefficient value of 0.99. It was also found that the vertical accuracy of the SRTM model is better than that of the ASTER model in the moderate slope area, where this accuracy reached 11.899m. In the case of the moderate steep slope area, the research found that the elevations extracted from the SRTM model are more accurate than those extracted from the ASTER model, with a vertical accuracy value of 21.609m for the SRTM model and 23.145m for the ASTER model. In the case of steep slope area, it was found that the elevations extracted from the ASTER model are more accurate than those extracted from the SRTM model, with a vertical accuracy of 36.770 meters for the ASTER model and 40.538 meters for the SRTM model.