Thermal-Based Remote Sensing Solution for Identifying Coastal Zones with Potential Groundwater Discharge

Abstract

Submarine Groundwater Discharge (SGD) is an essential process of the hydrological cycle by hydraulically connecting the land and sea. However, the occurrence, importance and effects of SGD remain largely underexplored. Here, we developed and validated a straightforward tool for mapping potential SGD areas in coastal ecosystems of Portugal. Our approach was based on the premise that relatively cooler groundwater discharging to warmer coastal waters manifests in the thermal band of satellite imagery acquired during the summer months. We then used Landsat 8 thermal infrared imagery (TIR) to derive sea surface temperature and standardized temperature anomalies maps. The results confirmed the capacity of TIR remote sensing for identifying SGD areas. The thermal analysis enabled us to acquire a useful visual-spatial correlation between the location of thermal anomalies and potentiometric surfaces of coastal aquifers. This way, over 20 potential SGD areas were identified. Our study makes an important contribute to our current SGD research status by developing a cost-efficient tool which can be used as a first level approach for large areas. Further investigation is needed to quantify the SGD and its potential effect in the receiving ecosystems, especially those located within environmentally protected areas.