Application of Satellite Imagery to Explore and Monitor Geothermal Systems

Abstract

SPOT and LANDSAT TM satellite imagery have been used to map surface manifestations associated with the Wairakei and Waiotapu geothermal systems in the Taupo Volcanic Zone, New Zealand. These manifestations include fumaroles, steaming and hydrothermally altered ground, and sinter. In both areas there are also distinctive patterns of geothermally stressed vegetation that extend over much larger areas than do most individual surface features. This stressed vegetation has reflectance characteristics different from those of the surrounding non-stressed vegetation that allow it to be distinguished on high spatial resolution SPOT (20 m) and LANDSAT TM (30 m) multispectral imagery. Though conventional SPOT XS and LANDSAT TM colour infrared band combinations can distinguish various surface features, they do not clearly separate thermally stressed from adjacent non-stressed vegetation. The fundamental discriminatory information is within the mid-infrared TM band 5 (1.55-1.75 pm). TM colour composite images that combine bands 5 and 4 (near-infrared) and a visible wavelength band (1, 2 or 3) allow such discrimination. A SPOT-TM hybrid image, created by combining the higher spatial resolution SPOT XS bands 2 and 3 with the TM band 5, yields better results. This evaluation shows that geothermally stressed vegetation provides a very good target for satellite remote sensing, which will aid exploration and monitoring geothermal systems in highly vegetated areas.