A History of Geothermal Energy Research and Development in the ...

EXPLORATION
5.3 Applied Terrestrial Remote Sensing Technology
EGI, the Great Basin Center for Geothermal Energy at the University of Nevada,
Reno (GBC), and LLNL, among others performed DOE-sponsored remote sensing
studies to support geothermal exploration and the geologic characterization of
geothermal systems. Studies covered topics ranging from geologic mapping to the
indirect identification of blind hydrothermal systems, and are grouped in four
general categories: 1) geothermal exploration model development, 2) exploration
for blind systems, 3) geologic characterization of geothermal areas, and 4) thermalanomaly
mapping.
5.3.1 Geothermal Exploration Model Development
DOE-supported scientists developed a knowledge-based digital geothermal
exploration model that covers most of the Great Basin. The model used analysis
of several spatially correlative data sets based on a geographic information system
(GIS). 131 Input data included hydrothermal alteration maps and lineament-fault
maps derived from LandSat Thematic Mapper data 132 , gravity data, aeromagnetic
data, geochemical data, locations of mining districts, locations of young igneous
lithologic units, heat-flow data, known geothermal occurrences, and topography.
Data were weighted and quantified using a GIS into a final geothermal potential
map. The results indicated that known geothermal systems could be located with
such a system. However, anomalies generated from such analyses always require
field-verification. Use of such a technique could in principle, speed explorationarea
selection and reduce costs. Such techniques can be generally applied to benefit
geothermal exploration programs in any geologic environment.
5.3.2 Exploration for Blind Systems
Applying remote sensing to locate blind geothermal systems—those with no evident
physical surface manifestations—focused on: 1) identifying vegetation affected
by upwardly migrating geothermal gasses (e.g., H 2
S and CO 2
) which are vented
at the Earth’s surface via fault and fracture systems; 2) geochemical anomalies
in soil produced from geothermal systems; 3) detection and characterization
of hydrothermal-alteration mineralogy; and 4) detection and mapping surface
evaporite minerals that may be related to hydrothermal convection.
Vegetation was analyzed using hyperspectral imaging—imaging which uses
hundreds to thousands of spectral bands—at: 1) several Nevada geothermal sites
where greasewood is the predominant vegetation, including Kyle Hot Springs,
Gabbs Valley, and Dixie Valley, Nevada; 2) Cove Fort-Sulphurdale, Utah, where big
sagebrush is the dominant vegetation type, 131/133-137 and 3) at Long Valley Caldera. 138
Significant vegetal-spectral differences were found near and over Kyle Hot Springs
and over faults in Dixie Valley near the current Terra-Gen Power production
area. Additionally, a vegetation anomaly was detected in Dixie Valley using data
52 A History of Geothermal Energy Research and Development in the United States | Exploration