Topographic normalization for improving vegetation classification in a mountainous watershed in Northern Thailand

Abstract

Land cover classifications are adversely affected by shading or topographic effects in mountainous areas in that the spectral properties of an entity in the shade appear to be different from those of the same entity in a sunlit area. Topographic effects can make it especially difficult to distinguish different successional stages of vegetation. The current work uses a simplified topographic normalization method to reduce the topographic effect and to improve land cover classification in a mountainous watershed in northern Thailand. Data used in the study were two Landsat 7 Enhanced Thematic Mapper Plus (ETM+) images acquired on 5 March 2000 and 7 February 2002, a digital elevation model, and Global Positioning Systems (GPS) ground truth data collected in July 2002 consisting of geographic location (latitude/longitude), feature information and ground reference photographs. A supervised land cover classification was conducted on original and normalized images. In general, the classification accuracy of the different successional stages of vegetation was improved in the normalized images.