UTILITY OF THERMAL INFRARED SATELLITE IMAGERY TO LOCATE GROUNDWATER DISCHARGE IN COASTAL LAGOONS

SGD is an important component of the hydrological and chemical cycles of coastal zones, yet it remains difficult to locate and quantify. Though several studies have used aerial thermal IR imagery from low flying planes to locate SGD, these studies are often expensive and time consuming. Thermal IR satellite imagery, however, may provide a quick and inexpensive method to locate this discharge. Thermal infrared images, acquired by Landsat 7 (60 m resolution) and ASTER (90 m resolution) satellites were used to locate known discharges of submarine groundwater (SGD) in two coastal lagoons: Venice Lagoon, Italy, and Great South Bay, USA. Analysis of the data was based on the large seasonal temperature differences between groundwater and surface water in the lagoon. Groundwater temperature is often stable and mediated by the average annual air temperature of the recharge basin. Shallow lagoons, conversely, often display a wide range in temperature. Venice Lagoon and Great South Bay are large, shallow mid-latitude lagoons, which have been extensively studied for SGD. Satellite images from the end of summer and winter were chosen, as these times represent the maximum temperature difference (~10°C) between ground-water and surface water. Despite the relatively low resolution of the images, compared to aerial IR, temperature anomalies were found in both lagoons. These anomalies, which could be potential sources of SGD, were compared to a series of radium measurements, a natural tracer of SGD, carried out in the study areas. The utility of the satellite data employed for identifying SGD plumes is discussed.