Unmanned aerial vehicles (UAVs)‐based thermal infrared (TIR) mapping, a novel approach to assess groundwater discharge into the coastal zone

Abstract

Submarine groundwater discharge (SGD) is a widely recognized process that carries considerable amounts of groundwater and dissolved chemicals to the coastal ocean. Despite its importance, a lack of suitable tools to assess SGD's spatial and temporal variability has hampered a complete understanding of the process. Here we report, for the first time, use of an unmanned aerial vehicle (UAV or "drone") to assess SGD variations. An octocopter UAV platform equipped with a thermal infrared (TIR) system was flown along a coastline on Jeju Island, Korea. The UAV clearly captured thermal signatures of SGD plumes and their dynamic temporal fluctuations modulated by tidal variations. Based on a plume area-SGD flux relation we developed by combining aerial and field data, we estimated that the SGD flux of the study site ranged from 33,000 to 54,000 m 3 d 21. The drone approach enabled acquisition of time series plume imagery with easy control of spatial resolution, flexible field operations, and remote sensing of SGD at low cost compared to conventional aerial surveys. Combining the UAV-TIR images with on-site sampling enables one to determine fluxes of nutrients and other dissolved species. UAV-TIR mapping can thus serve as a powerful tool for study of SGD and other coastal processes.

Assessing the potential of drone‐based thermal infrared imagery for quantifying river temperature heterogeneity

“…sUAS‐based TIR enables repeatable, low‐altitude surveys at lower cost than “conventional” (i.e., helicopter/aeroplane based) airborne TIR (Lee et al, ) while producing high‐resolution images captured at nadir. Although these merits make sUAS‐based TIR an attractive method for thermal imaging of waterbodies, susceptibility to within‐image and interimage temperature biases presents an impediment to the extraction of true temperature data.…”

“…These discrete inputs of cool or warm water often play a crucial role in the provision of thermal refuges (Daigle, Jeong, & Lapointe, ; Ebersole, Wigington, Leibowitz, Comeleo, & Sickle, ; Kurylyk, MacQuarrie, Linnansaari, Cunjak, & Curry, ). Despite the wealth of river temperature data that TIR has generated (Dugdale, Bergeron, & St‐Hilaire, ; Fullerton et al, ; Tan & Cherkauer, ) and its role in improving process‐based understanding of river temperature heterogeneity, TIR surveys of river corridors remain relatively costly, making it difficult to justify their use along shorter reaches or for multitemporal surveys (Lee et al, ).…”

Quantitative estimation of submarine groundwater discharge using airborne thermal infrared data acquired at two different tidal heights

“…Furthermore, we compared the estimated SGD flow rate from airborne TIR data with the measured SGD flow rate using a current meter at Gongcheonpo Beach (Flowatch, JDC) during the low tides on August 5, 2015 (E. Lee, Yoon, et al, ). There were two areas with the SGD signal at Gongcheonpo Beach, and the estimated SGD flow rates at two points were 147.8 ± 24.2 and 821.6 ± 56.3 m 3 /hr, whereas the measured SGD flow rates were 162.4 ± 10.5 and 874.8 ± 14.3 m 3 /hr in low tide.…”

“…In this study, we conducted experiments on three sites (Figure ): (a) Kimnyung Bay is located on the northern coast of Jeju Island, where Cheonggulmul, near Kimnyung Bay, has long been known for its natural outdoor bathing pool due to abundant groundwater discharge; (b) Bangdu Bay, on the eastern coast, is also an active site for SGD, known to play a major role in nutrient budgeting from SGD (Hwang et al, ); and (c) Gongcheonpo Beach, on the southern coast, is characterized by fractured volcanic rocks with point‐source groundwater discharges (E. Lee, Yoon, et al, ). These are highly suitable and important sites for studying the characteristics of SGD on a regional scale.…”

Efficient hydrogeological characterization of remote stream corridors using drones

“…Such exchange zones, particularly those of groundwater discharge, can now be located with a variety of hand‐held remote sensing tools (Briggs & Hare, ). Specifically, thermal infrared (TIR) sensing at times of surface‐water and groundwater temperature contrast can yield unprecedented detail regarding nonsubmerged preferential discharge on the scale of centimetres to watersheds (Dugdale, ; Fullerton et al, ; Lee et al, ). Sufficient thermal contrast for the identification of discharge typically exists away from the equator in summer and winter, in late afternoon or early morning, respectively.…”