A review of various analytical techniques for estimating subsurface heat flow regimes from aero-geophysical data

The present review x-rays the various analytical techniques for identifying, mapping, and estimating subsurface heat flow regimes from airborne geophysical data. The airborne geophysical techniques reviewed are the electromagnetic, gravity, magnetic, radiometric, and satellite remote sensing. Each of the reviewed geophysical techniques measures different subsurface Earth’s property indirectly through inversion techniques. The airborne electromagnetic study measures the electrical and magnetic properties of subsurface materials, while the airborne gravity survey measures the density contrast of subsurface materials. Also, while the airborne magnetic technique measures the magnetic susceptibility of subsurface rocks, the airborne radiometric survey measures the radioactive content of rocks. These geophysical properties (electrical conductivity, magnetic susceptibility, and density) are not measured directly but are estimated through the inversion of acquired geophysical data. Similarly, satellite imageries acquired from remote sensing records the spectral signatures of surface materials based on their various interactions with electromagnetic radiations. These techniques have been extensively applied worldwide by several researchers for various exploration and regional studies including mineral exploration, regional tectonic studies, and geothermal evaluation. In geothermal studies, Curie point depth, geothermal gradient, and heat flow have been derived from magnetic data using spectral inversion techniques, while radiogenic heat production can be estimated from radiometric data. Satellite remote sensing data typically analyzes spectral signatures of near surface materials for mapping of hydrothermal alterations, surface deformation, structural deformation, land surface temperature, geobotanic indicators, and other indicators. By analyzing these properties, it is possible to infer geothermal plays, evaluate the geothermal resource potentials, and locate prospective reserves for geothermal drilling operations. This study therefore aimed at assessing the strengths and weaknesses of the various techniques. The results of this study have revealed that no single technique is self-sufficient. The integration of multiple techniques can provide a more robust study leading to accurate and precise location of reserves for drilling programs, thus aiding in the exploration and development of geothermal energy resources.