Combining continuous spatial and temporal scales for SGD investigations using UAV-based thermal infrared measurements

Abstract

Abstract. Submarine groundwater discharge (SGD) is highly variable in spatial and temporal terms due to interplay of several terrestrial and marine processes. While discrete in-situ measurements provide a continuous temporal scale to investigate underlying processes and thus accounts for temporal heterogeneity, remotely sensed thermal infrared radiation sheds light on the spatial heterogeneity as it provides a continuous spatial scale. Here we report results of the combination of both, the continuous spatial and temporal scales, using the ability of an Unmanned Aerial Vehicle to hover above a predefined location and the continuous recording of thermal radiation of a coastal area at the Dead Sea (Israel). With a flight altitude of 65 m above the water surface resulting in a spatial resolution of 13 cm and a thermal camera (FLIRTau2) which measures the upwelling long-wave infrared radiation at 4 Hz resolution we are able to generate a time sequence of thermal radiation images which allows us to analyse spatiotemporal SGD dynamics. In turn, we are able to enhance focused SGD spots otherwise being camouflaged by strong lateral flow dynamics that may not be observed on single thermal radiation images. Plus, we show the spatiotemporal behavior of a SGD induced thermal radiation pattern to vary in size and over time by up to 55 % for focused SGDs and by up to 600 % for diffuse SGDs due to different underlying flow dynamics. These flow dynamics even display a short-term periodicity in the order of 20 to 78 s for diffuse SGD which we attribute to an interplay of conduit maturity/geometry and wave setup.

Drones address an observational blind spot for biological oceanography

“…At the same time, researchers are adopting drones to observe fine-scale physical oceanography. Example applications include examining boundary layer processes (Zappa et al 2020), observing ocean-atmosphere interactions (Cassano et al 2016), and monitoring groundwater discharge through thermal imagery (Mallast and Siebert 2018).…”

“…2020), observing ocean–atmosphere interactions (Cassano et al . 2016), and monitoring groundwater discharge through thermal imagery (Mallast and Siebert 2018).…”