Applicability of Landsat 8 thermal infrared sensor for identifying submarine groundwater discharge springs in the Mediterranean Sea basin

Submarine groundwater discharge (SGD) has received increasing attention over the past two decades as a source of nutrients, trace elements, and ocean pollutants that may alter coastal biogeochemical cycles. Assessing SGD flows and their impact on coastal marine environments is a difficult task, since it is not easy to identify and measure these water flows discharging into the sea. The aim of this study is to demonstrate the significant usefulness of the freely-available thermal infrared (TIR) imagery of the Landsat 8 thermal infrared sensor (TIRS) as an exploratory tool for identifying SGD springs worldwide, from local to regional scales, for long-term analysis. The use of satellite thermal data as a technique for identifying SGD springs in seawater is based on the identification of thermally-anomalous plumes obtained from the thermal contrasts between groundwater and sea-surface water. In this study we use the TIR remote sensing (TIR-RS) imagery provided by Landsat 8 at a regional scale and discuss the principle limiting factors of using this technique in SGD studies. The study was developed in karstic coastal aquifers in the Mediterranean Sea basin during different seasons and under diverse meteorological conditions. Although this study demonstrates that freely-available satellite TIR remote sensing is a useful method to identify coastal springs in karst aquifers both locally and regionally, the limiting factors include technical limitations, geological/hydrogeological characteristics, environmental and marine conditions, and coastal geomorphology.This work was partly funded by the Spanish Government (grant nos. PID2019-110212RB-C22 and PID2019-110311RB-C21) the “Maria de Maeztu” program for Units of Excellence (grant no. CEX2019-000940-M) of the Spanish Government and the project TerraMar (grant no. ACA210/18/00007) of the Catalan Water Agency. The authors want to thank the support of the Generalitat de Catalunya to GHS (grant no. 2017 SGR 1485) and MERS (grant no. 2018 SGR-1588) for additional funding.Peer ReviewedPostprint (published version