Fusing Landsat-5/TM Imagery and Shaded Relief Maps in Tectonic and Geomorphic Mapping

Abstract

The significance of both solar elevation angle and azimuth are critical elements for examining Earth observation datasets. Illumination angle is a crucial parameter affecting the appearance of the topographically related and dependent features. Therefore, an improved methodology of data fusion for tectonic and geomorphic mapping is needed to augment the traditional false color composite analysis. A long-standing problem in such applications is the bias introduced by illumination geometry, specifically sun elevation and azimuth. A Landsat-5 image of Lesvos Island, Greece, was combined with digital elevation models to produce fused images with a wide range of illumination azimuths and elevation in a GIS environment. Sixteen combinations of sun elevation angle (using 15° and 30°) paired with azimuth (0° to 360° at 45° increments) were considered. This new technique compensates for local conditions such as generally cloudy winters which make it difficult to obtain images with low sun elevation or images of eroded landforms with subdued geomorphic expression. The resulting fused images combine the tonal information and high spatial resolution of Landsat with the strong topographic rendition of digital elevation models. Well-known faults, with more or less significant expression on the surface known from previous image interpretation and fieldwork, are more easily identifiable. Shaded relief maps produced by applying the lower illumination angle in combination with an azimuth perpendicular to the fault orientation produced the best results. Additionally, previously unknown linear and circular features, e.g., calderas, were represented in the low illumination angle image, independent of its azimuth. Fused images will be further combined with geologic and seismicity maps to study problems such as location of the Anatolian Plate’s boundaries and their nature (sharp or diffuse).