Analysis of catchment hydrogeomorphology and vegetation patterns based on a differential GPS survey and interferometric SAR

To better understand the effect of vegetation on hydrogeomorphic processes, detailed studies on terrain properties and vegetation patterns performed at the catchment scale are needed. These studies require high resolution topography data (<5 m) in order to accurately capture the variability of the terrain and to successfully link it to vegetation patterns. Hydrologic and terrain analyses were performed on a small (~0.1 km2) first order semiarid basin in central New Mexico. The catchment exhibits opposing north versus south facing slopes, giving rise to different ecosystems and geomorphic properties, with an east facing headslope comprising an ecotonal boundary. A high precision (5 cm in x, y, z) differential global positioning system (GPS) was used to generate a digital elevation model (DEM) of the catchment using nearly 6,000 independent observations. This high resolution DEM is used to perform a set of topography-based analyses on the current hydrologic and geomorphic properties of the basin. We discuss the GPS survey methods employed in the field, data post- processing and various interpolation approaches utilized for gridding the point data. We then perform a series of hydrogeomorphic analyses based on different terrain indices such as the TOPMODEL index, and address the issue of scale by comparing results from the GPS derived DEM with a 10 m DEM from the Interferometric Synthetic Aperture Radar (IFSAR). Finally, a 1 m orthophoto is used to perform a supervised classification of the spatial arrangement of vegetation in the area and the relationship to the hydrologic and terrain indices is explored. Our results indicate substantial differences exist in terrain properties derived from GPS and IFSAR products. These differences can potentially lead to divergent conclusions on the investigation of vegetation pattern influences on hydrogeomorphic properties of basins. The results obtained point to the need for higher resolution DEMs than IFSAR for studying vegetation-hydrogeomorphic interactions at the catchment and hillslope scale. The advent of new high precision surveying technologies such as DGPS and LIDAR may open new possibilities for the exploration of land cover properties effects on the hydrologic and geomorphic characteristics of the terrain.