Effects of topography on radiance from upland vegetation in North Wales

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Abstract
Radiance data from a Landsat 5 Thematic Mapper image were used to study terrain effects in 284 4 pixel by 4 pixel quadrats in upland North Wales. The three semi-natural vegetation types examined responded differently to variations in slope and aspect. Short-cropped Agrostis grassland was the most uniform type and it reflected radiation in a solar-orientated diffuse manner. Variations in radiance detected from two rougher vegetation types suggested environmentally induced heterogeneity within the vegetation cover, related to aspect (Nardus grassland) or slope (Calluna heathland). The difference between reflected red and green light is proposed as a crude measure of photosynthesis that can discriminate between broad vegetation categories in undulating terrain.