The utilisation of merged remotely sensed data for geomorphological investigations in the desert of central Saudi Arabia

Image merging has gained acceptance in geological remote sensing. However, it has rarely been applied in geomorphology. This research reports on the usefulness of the merging data of high spatial resolution (SPOT PAN and IRS PAN) with multispectral TM imagery in mapping commonly encountered desert geomorphological features and in relative age dating of alluvial surfaces. The merged data were applied to the identification and mapping geomorphological features along two geologically different mountain fronts in Central Saudi Arabia. Three types of geomorphological maps have been created: 1) a morphogenetic map that distinguishes between aeolian landforms, fluvial landforms, desert pavements, and gypsum crusts 2) a morphochronological map, which shows the relative age of six outwash plains develop along the eastern edge of the Arabian Shield and 3) a morphochronological map, which shows the relative age of four geomorphic surfaces developed on an alluvial fan in the Uraidan area. The construction of these maps is supported by field observations and laboratory measurements. The ability of three merging methods (PCS, multiplicative and Brovey transformation) to identify landforms were statistically and visually evaluated. The optimum merging technique for merging PAN and TM data to delineate desert landforms was PCS, followed by Brovey Transformation and multiplicative. Using the optimum index factor (OIF), a IRS PAN/TM band 1, 5 and 7 image (of 20 merged composites) was found to be the optimum colour composite image for the geomorphological features in this arid environment. These findings are discussed in the context of the spatial and spectral properties required for (applied) geomorphological remote sensing. Determination of the age relationships of palaeogeomorphic processes is critical for the interpretation of the geomorphological history and the assessment of the spatial and regional extent of changes in this unstudied desert region. This research shows that the OSL dates and historical records indicate that the geomorphic processes in the eastern edge of the Arabian Shield of central Saudi Arabia were responding to global shifts in climatic conditions. A short wet interval at 0.85 0.1 ka B.P. can be attributed to a shift of the monsoon northwards as a result of increased temperatures, rising in sea levels and increased evaporation of the oceans during the Little Optimum.