Geological and Geomorphological Applications of Low-Angle Illumination Satellite Imagery in Northern Ireland

Abstract

Some geoscientists consider satellite imagery as having limited research potential due to their inability to elicit useful information. However, their lack of information extraction is often partly caused by a poor understanding of the importance of such parameters as illumination angle or waveband selection. For the analysis of geological or geomorphological features in vegetated terrain, high-angle illumination imagery acquired between March and October reveals little information. However, low-angle illumination imagery (<10° solar elevation) obtained in December clearly displays many geomorphological and geological structures not apparent at a higher sun angle. The North Antrim End Moraine can easily be mapped as a single feature on a December image. The Tempo-Sixmilecross Fault and Omagh Fault can also be readily mapped at low-angle illumination and the spatial relationships of these faults to associated structures readily determined. In vegetated terrain Thematic Mapper band 5 is superior to Thematic Mapper band 4 for information extraction. This is partly due to the lower reflectance variance for vegetation on Thematic Mapper band 5 compared with Thematic Mapper band 4, thus the continuity of features is not disrupted.