Detection and monitoring of thermal anomalies using Satellite-based thermal infrared time series data in the Eburru Geothermal prospect area, Kenya

Abstract

Thermal anomalies are associated with electromagnetic radiation emitted from the surfaces of different materials. By observing the temperature contrast among different objects within a specific surrounding, it is possible to pinpoint the areas with elevated temperature measurements. In geothermal environments, data associated with areas of stress regimes, are usually characterized by surface manifestation features such as fumaroles, hot grounds, steam vents. As such, information derived from such measurements helps in the comprehension of mass flow, degassing regimes, and changes in barometric pressures associated with geothermal systems. This makes it possible to characterize the geothermal systems. Different methods are used for thermal measurements of thermal features. Field-based techniques are the most common techniques are used for such studies. However, these approach is limited in scope, with regards to repeatability, and in some instances inability to access zones with rugged terrains. The availability of long-term global satellite data (imageries) offers an alternative way of thermal measurements. The method is convenient due to its ability to estimate land surface temperature over large areas of coverage, in a relatively short time. By monitoring the fluctuation of temperature values of specific pixels, over time it is possible to understand the thermal history of specific hotspot zones, within an area of interest. For this study, thermal bands of the multispectral Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images acquired between 2008 and 2018, were tested at known geothermal hotspots zones within the Eburru Geothermal prospect area. In addition, specific points from non-geothermal zones (e.g., known vegetated areas and zones with normal surface temperatures) were used as control points. Emphasis was placed on night time scenes, to reduce the effects of solar illumination. The amplitudes of the time series plots show consistency over time, an indication that minimal changes have occurred in geothermal hotspot zones. However, the time series curves of pixels from non-geothermal areas exhibit inconsistent fluctuation of the amplitudes, an indication that other factors (mainly weather) affect their thermal behavior. Future studies should incorporate time-series data from ground measurements from heat loss survey measurements to validate of study’s findings. In addition, hyperspectral thermal data will be useful in precise monitoring of the surface thermal behavior, in the area.