RETRIEVAL OF SUBMARINE GROUNDWATER DISCHARGE FLOW RATES USING AIRBORNE THERMAL INFRARED DATA ACQUIRED AT TWO DIFFERENT TIDAL HEIGHTS

摘要

Submarine groundwater discharge (SGD) plays an important role in coastal biogeochemical processes and hydrological cycles, particularly off volcanic islands standing in oligotrophic oceans. However, limited access of SGD measurements over a large scale prevents from fully understanding the spatio-temporal variations. This study tries to quantify the temporal and spatial variations of SGD using four airborne thermal infrared (TIR) surveys over the entire coast of Jeju Island. Korea. The surveys were done twice, each during high and low tide, and the data showed a linear correlation between the temperature anomaly and squares of groundwater velocity and a negative exponential correlation between the anomaly and depth (included tide height and bathymetry). Using these relationships, a new analytic equation for estimating the SGD flow rates using temperature anomaly at any tide height was derived. The method was validated using the measured SGD flow rates with in-situ measurement using a current meter at Gongcheonpo Beach. Despite difficulty of the on-site observation of SGD flow rates, the SGD flow rates were directly retrieved using the temperature anomaly in combination with high-resolution coastal bathymetry map and tide height. This approach is expected to be applied to rapid and efficient estimation of SGD over coastal areas off oceanic islands where fresh groundwater discharge is significant and results in great impact on coastal ecosystems.