Description:
<jats:p>Abstract. 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.
</jats:p>