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

Mallast, Ulf; Siebert, Christian

Submarine groundwater discharge (SGD) is highly variable in spatial and temporal terms due to the interplay of several terrestrial and marine processes. While discrete in situ measurements may provide a continuous temporal scale to investigate underlying processes and thus account 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 (UAV) 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 (FLIR Tau2) that measures the upwelling long-wave infrared radiation at 4 Hz resolution, we are able to generate a time series of thermal radiation images that allows us to analyse spatio-temporal SGD dynamics.

In turn, focused SGD spots, otherwise camouflaged by strong lateral flow dynamics, are revealed that may not be observed on single thermal radiation images. The spatio-temporal behaviour of an SGD-induced thermal radiation pattern varies in size and over time by up to 155 % 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 of the order of 20 to 78 s for diffuse SGD, which we attribute to an interplay between conduit maturity–geometry and wave set-up.

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Zitierform:

Mallast, Ulf / Siebert, Christian: Combining continuous spatial and temporal scales for SGD investigations using UAV-based thermal infrared measurements. 2019. Copernicus Publications.

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