| Digital elevation models (DEMs) provide the basic information required to characterise the topographic attributes of terrain. The primary derived topographic parameters associated with DEMs are slope and aspect. Slope and aspect can be used to calculate other significant topographic parameters such as upslope area and topographic index. The topographic index, in turn, can be used by distributed hydrological models, such as TOPMODEL, to characterise the spatial distribution of terrain. Many algorithms have been developed to calculate slope; aspect and upslope area from DEM s—specifically from gridded DEMs—but little work has gone into determining the uncertainty in these parameters, or the effect of this uncertainty in further applications. The accuracy of these parameters is dependent both on the algorithm used to generate them, and on the errors associated with the DEM itself. Since it is almost impossible to model all the errors associated with a given slope, aspect or upslope area algorithm, and since a DEM is normally only provided with a single rms error, simple error propagation is not adequate to determine the error associated with the derived topographic parameters. A more rigorous method of determining the effect of DEM errors on derived topographic parameters is with statistical analysis using Monte Carlo simulation and error realisations of the DEM. In this research, a comparison of slope, aspect, upslope area, and topographic index algorithms are presented along with an examination of how errors in DEMs effect the reliability of the derived topographic parameters. The effect of errors in the derived topographic parameters on the TOPMODEL hydrological model is also examined. |
