High‐resolution aerial infrared mapping of groundwater discharge to the coastal ocean

Abstract

Submarine groundwater discharge (SGD) is a principal pathway for nutrient and contaminant entry into coastal zones worldwide. The ability of SGD to transport dissolved constituents, and the spatially and temporally variable nature of SGD, require rapid and high‐resolution data acquisition at the scales in which it is commonly observed. Airborne thermal infrared (TIR) remote sensing is uniquely qualified for this task, and is applicable wherever > 0.1°C temperature contrasts exist between discharging and receiving waters. We investigated SGD on three of the largest Hawaiian Islands, including most of Oahu, much of western Hawaii, and most of western Maui. The resulting images are 0.5 to 3.2 m‐resolution sea‐surface temperature maps that are accurate to 0.7°C. In this article, we lay the foundation for a complete methodology of TIR data collection, post‐flight data processing, and image interpretation for groundwater discharge research. We demonstrate that groundwater plume areas are linearly and highly correlated to in situ groundwater fluxes. These results illustrate the potential for volumetric quantification and up‐scaling of small‐ to regional‐scale SGD. These methodologies provide a tremendous advantage for identifying and differentiating point‐source and diffuse groundwater discharge into oceans, lakes, and streams. The techniques are also important precursors for developing best‐use strategies for time‐consuming in situ studies, and represent a substantial new asset for those concerned with coastal‐zone research, planning, and management.

Integration of aerial infrared thermography and in situ radon‐222 to investigate submarine groundwater discharge to Pearl Harbor, Hawaii, USA

“…We followed the post‐flight data processing methods described by Kelly et al (). Succinctly, data were temperature‐corrected to blackbody calibrations, mosaicked, georeferenced, annotated (digitized) to retain only the water temperature signature, corrected to in situ measurements of temperature (HOBO pendant UA‐001‐08; Onset, Cape Cod, Massachusetts), colorized with false color, and draped over 0.3 m georectified, visible‐light orthoimages obtained from the United States Geological Survey (https://www.sciencebase.gov/catalog/item/59f0ce05e4b0220bbd9bf77d).…”

Investigation of submarine groundwater discharge to tidal rivers: Evidence for regional and local scale seepage

“…Previous studies have utilized a variety of remote sensing platforms to investigate groundwater discharge patterns and rates under different hydrogeologic regimes, including point‐source (Kelly et al ., ) and diffuse SGD (Lee et al ., ) in a volcanic environment (Hawaii and Jeju Island, Korea, respectively), diffuse SGD from a permeable unconfined coastal aquifer (Long Island Sound, NY; Tamborski et al ., ), and from freshwater springs (Prince Edward Island, Canada; Danielescu et al ., ). To utilize TIR remote sensing techniques for hydrologic investigations, it is necessary that a wide variety of hydrologic environments under a range of environmental conditions be thoroughly studied.…”

“…Methods for quantifying SGD fluxes include numerical water balances, seepage meter measurements, and geochemical tracers (Burnett, Peterson, Santos, & Hicks, ), but thermal infrared (TIR) remote sensing has a proven utility in identifying SGD (Johnson, Glenn, Burnett, Peterson, & Lucey, ; Kelly, Glenn, & Lucey, ). Dugdale () recently reviewed the application of TIR remote sensing for hydrological studies of rivers and streams.…”

“…The amount of river water derived from local groundwater discharge can be estimated via energy‐conservation applied to TIR imagery, as demonstrated to the Heihe River, China (Liu, Liu, Hu, Wang, & Zheng, ). The two‐dimensional surface area of a sea‐surface TIR anomaly was found to be positively correlated with point‐source SGD along the Hawaiian coast (Kelly et al ., ) and with nonpoint‐source diffuse fresh SGD along Long Island Sound, NY (Tamborski, Rogers, Bokuniewicz, Cochran, & Young, ). As a result, TIR imagery can be applied as a quantitative tool toward upscaling groundwater discharge fluxes on a regional basis.…”

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

“…Detection of SGD from TIR remote sensing is possible in any environment where there is significant thermal contrast between the discharging pore fluid and the receiving surface water body (Tamborski, Rogers, Bokuniewicz, Cochran, & Young, ). Airborne TIR remote sensing has been used in an attempt to show the spatial variability of SGD at higher spatial resolutions than space‐borne TIR imagery is capable of demonstrating (Bejannin, van Beek, Stieglitz, Souhaut, & Tamborski, ; Kelly, Glenn, & Lucey, ; Mejías et al, ; Mulligan & Charette, ; Tamborski et al, ). Our research team has previously presented the possibility of detecting SGD around Jeju Island using airborne TIR imagery (E. Lee, Kang, et al, ).…”