Spatial Aggregation of Complex Terrain

Abstract

Distributed component simulations of watersheds seek to represent the terrain as a contiguous set of functional units such as hillslopes or subcatchments with distinctive hydrologic responses. The partition should capture the significant geographic patterns of watershed response by maximizing the proportion of the topographic and surface cover variance that exists between units and minimizing the proportion that exists within units. This has the effect of minimizing the effort of simulation that must be allocated to each drainage area. At the same time, the number of hillslopes should be limited to avoid too many consumptive model preparations and executions. The segmentation strategy may be guided and controlled by an understanding of the scale dependence of hillslope complexity, estimated by tracking the behavior of descriptive spherical statistics of the surface over a range of partition levels. Spherical statistics are used as they have strong bearing on the definition of uniform topographic facets, microenvironment, and the signal recorded by a remote sensor as influenced by the distribution of the surface normal. Digital terrain models are used to automate the partition of the watershed into different sets of hillslopes and for the computation of topographic complexity within and between units. The behavior of the surface variances over the range of sample scales is strongly related to the stream network structure and is expected to take on distinct forms that are characteristic of different geomorphic environments. 1989 The Ohio State University