UNCERTAINTY AND EFFECTS OF RESOLUTION OF DIGITAL ELEVATION MODEL AND ITS DERIVED FEATURES: CASE STUDY OF SUMBERJAYA, SUMATERA, INDONESIA

摘要

Hydrological and erosion studies in Way Besai watershed in Sumberjaya, West-Lampung, Sumatera, Indonesia, require assessment of slope and flow pathways. A Digital Elevation Model (DEM) was generated from aerial photographs (1:24.000) using a softcopy photogrammetry approach. Error of elevation in a DEM affects derived slope, topographic index and catchment boundaries. Propagation of elevation error was evaluated on slopes both in a relatively flat terrain as well as in an undulating one. True elevation is unknown, but error can be estimated from uncertainty assessed with statistical methods following Monte Carlo simulation approach. Statistics grids as well as single parameters resulted were analyzed. Effects of DEM uncertainty on the derived slope is more pronounced in the flat terrain than in the undulating one. Within the scope and assumptions of this study, the effect of resolution on the slope uncertainty shows that higher resolution DEM creates larger slope uncertainty. Incorporation of spatial dependence in the assessment of error propagation has strong effects on the apparent error of slope. Therefore, spatial dependence of DEM uncertainty should be considered when assessing error in spatial data, especially if slope is to be derived from the DEM.