Detection of Submarine Groundwater Discharge (SGD) Signal by Stacking Landsat Thermal Infrared (TIR) Images in Jeju Island

Abstract

Although submarine groundwater discharge (SGD) has recently attracted, dispersive and weak SGD signals have not been satisfactorily identified. Since SGD varies spatially and temporally, the locations of SGD are generally hard to detect from a single satellite image. Due to such spatiotemporal characteristics, multi temporal data are required to detect SGD appeared in various patterns and weak amplitudes. Additionally, weak SGD signals may be missed on a single satellite image as they may fall below the noise threshold dictated by Landsats noise equivalent differential temperature (NEdT). Thus, this study proposes a practical method by applying stacking method to Landsat data for SGD detection. The stacking method is comprised of two main processing steps: 1) mask out the land area and calculate sea surface temperature (SST) anomalies by subtracting the offshore SST, and 2) stack SST anomalies by summing multiple images. The optimal seasonal and tidal conditions for the detection of a weak SGD signal were determined, and then Landsat images satisfying the conditions of month and tide level were stacked in order to strengthen SGD signals and confirm the presence of SGD. In this study, the method was applied to three sites on Jeju Island. The results show that this method is very successful at detecting SGD signal, even for weak signals.