UAV in combination with a thermal infrared sensor for the use in
groundwater research
Abstract
Submarine groundwater discharge (SGD) is highly variable in spatial and
temporal terms due to interplay of several terrestrial and marine
processes. In contrast to discrete in-situ measurements, remotely sensed
thermal infrared radiation has proven to reveal horizontal SGD
variability in a spatially continuous context. Yet, it lacks temporal
information that is crucial to understand highly dynamic systems as
represented by many coastal environments. Here we report the results of
temporal continuous Unmanned Aerial Vehicle (UAV)-based measurements of
thermal radiances in a highly saline environment - the Dead Sea. Instead
of flying over the study area we exploit the UAV ability to observe
predefined locations by hovering above a predefined SGD spot to study
spatio-temporal characteristics of SGD. Through hovering and the so
obtained high temporal and spatial resolution of thermal radiances, we
can show influences of crossflows and interaction of nearby SGDs on the
final thermal radiance pattern, horizontal pattern shifts, pattern size
variation of up to 600% and a periodic discharge behaviour at intervals
of 20-78 seconds. These numbers could not be revealed with classical
spatially discrete methods and thus mean an asset for groundwater
discharge and process understanding. Besides the advantages and thus
opportunities for groundwater investigation, we will likewise point out
limitations during the conduction (flight stability, flight duration,
thermal sensor drift) and processing (image registration) but also
future improvements that may influence UAV-based groundwater
investigations.