Using Palsar imagery for characterizing natural properties of volcanic conduits in the Ethiopian volcanic province
(1) University of Nantes, 2 rue de la houssinière, 44322 Nantes, France
In large volcanic provinces, such as the Ethiopian Traps, the magmas erupt from vertical conduits (dykes) at high magma effusion rate. The high degassing rate is thought to result in major, though transient, climatic changes. Dykes are also intensely fractured rock sheets in which aquifers preferentially develop. Water availability during the dry season is a crucial issue for the development of this rural and remote area of Ethiopia.
The ethio-sudanese plain west of lake Tana, Ethiopia, is being investigated in order to assess the use of Alos/PALSAR and PRISM imagery in dyke identification, and attempt to understand which radar-derived natural properties are actually imaged (roughness, topography, associated vegetation, moisture).
Dyke aspect ratio in map view is high (typically length/thickness is 103), and the thickness of most of them is on the order of a few meters or less. The dykes are not easily identified from composition differences with the surrounding terrains in Ethiopia because they are usually surrounded by the lava flows they fed. At the present stage of the study, Alos/PALSAR imagery of various polarization modes has been compared to Envisat/ASAR (band C), SIR-C (bands C and L) imagery, as well as Vis-IR images from Landsat TM, Aster, Spot 5, and Quickbird. The strength and weaknesses of these datasets in retrieving dykes, their orientation, and length will be presented, as well as some results as to the dyke properties observed by Palsar. The interpretations are constrained by field work that could be carried out over portions of the study area.