| Title | Quantifying Surface Roughness to Detect Geothermal Manifestations from Polarimetric Synthetic Aperture Radar (PolSAR) Data |
|---|---|
| Authors | Asep SAEPULOH, Katsuaki KOIKE, Mohamad Nur HERIAWAN, and Taiki KUBO |
| Year | 2016 |
| Conference | Stanford Geothermal Workshop |
| Keywords | Surface roughness, PolSAR, ALOS PALSAR, geothermal, Wayang Windu |
| Abstract | Spatial mapping of geothermal-resource potential with an accurate detection of steam spot using remotely-sensed technology requires quantification of physical parameters of surface manifestation related to geothermal system. Synthetic Aperture Radar (SAR) remote sensing, the only useful observation and monitoring technology that can be undertaken in any weather condition, measures backscattering powers returned to a satellite sensor. The backscattering is mainly controlled by the surface roughness that is related to rock types. Resistance to the geological processes such as weathering, erosion, and alteration is different with rock type, which causes a dependence of the surface roughness upon rock type. The backscattering is also affected by dielectric permittivity and magnetic permeability of the ground surface. The purpose of this study is to develop methods for quantifying the surface roughness from the SAR data and detecting surface manifestations of geothermal based on the roughness. A surface roughness dataset by ground-truthing in a geothermal field using a profiler of 30 cm length was used to verify the estimated roughness. Detrending and interleaving techniques of the surface profile were applied to quantify accurately the surface roughness. Correlations of the measured surface roughness with the polarized backscattering intensity and the incidence angle were investigated, which was finally used to make a physical model by a curve fitting of 269 data points. The resultant model was applied to map a spatial distribution of the surface roughness over a 72 km2 area in the Wayang Windu geothermal field, West Java, Indonesia using two scenes of Full Polarimetric mode of the Phased Array L-band Synthetic Aperture Radar (PALSAR) onboard Advanced Land Observing Satellite (ALOS). Both the ground-truthing and the SAR roughness data indicated that the roughness increased and decreased gradually towards the altered surface manifestations. The rock types and thermal intensities of hydrothermal fluid controlled the surface roughness in general. For lava and pyroclastic rocks, hydrothermal fluids have altered the rock matrices into clay minerals that are easily eroded. The rock fragments are more resistant than rock matrices at ground surfaces. Consequently, surface of the altered rocks becomes rough than the intact rocks in general. For tuff and lahar deposits, hydrothermal fluids have altered all the rock compositions into clay minerals and produced flat surfaces. |