| Abstract |
Temperature measurements at a two-meter depth have been proven effective for identifying thermal anomalies caused by shallow thermal groundwater plumes and steam-heated ground associated with geothermal systems, even where no surface manifestations are present. Nevertheless, significant non-geothermal temperature anomalies at a 2-meter depth can be produced by variations in surface solar radiation input (caused by variations in albedo and topographic slope aspect), climate (e.g. elevation lapse rate), and variations in the thermal diffusivity of soils and rocks. These non-geothermal temperature variations can either obscure underlying contributions of geothermal heat flux or have the potential to be misinterpreted as geothermal anomalies. In this paper, we review the development status of data processing methodologies for minimizing non-geothermal temperature anomalies so that geothermal heat flux can be more accurately identified and mapped. These methodologies rely on auxiliary data, including digital elevation models (for determining elevation and slope aspect), visible-light remote sensing images (for estimating albedo), shallow temperature gradient measurements (also for estimating the effects of albedo and topographic slope), and in-situ 2-meter transient heat decay tests (for estimating thermal diffusivities). An example is provided wherein thermal diffusivities are estimated for the Desert Queen area of northwestern Nevada using multiple 2-meter temperature measurements over the course of a year. In this case, the impact of thermal diffusivity on the 2-meter temperature anomaly appears insignificant, but surveys completed at other locations, particularly during mid-summer, have identified stronger influences. Laboratory testing shows that established methods of making in-situ thermal diffusivity measurements can be adapted to the current 2-meter probe design in use at the Great Basin Center for Geothermal Energy. The routine use of such devices will facilitate rapid and detailed compensation for thermal diffusivities without the need for additional temperature measurements at greater depths or over longer periods of time. |