Combining Remote Temperature Sensing with in-Situ Sensing to Track Marine/Freshwater Mixing Dynamics

Abstract

The ability to track the dynamics of processes in natural water bodies on a global scale, and at a resolution that enables highly localised behaviour to be visualized, is an ideal scenario for understanding how local events can influence the global environment. While advances in in-situ chem/bio-sensing continue to be reported, costs and reliability issues still inhibit the implementation of large-scale deployments. In contrast, physical parameters like surface temperature can be tracked on a global scale using satellite remote sensing, and locally at high resolution via flyovers and drones using multi-spectral imaging. In this study, we show how a much more complete picture of submarine and intertidal groundwater discharge patterns in Kinvara Bay, Galway can be achieved using a fusion of data collected from the Earth Observation satellite (Landsat 8), small aircraft and in-situ sensors. Over the course of the four-day field campaign, over 65,000 in-situ temperatures, salinity and nutrient measurements were collected in parallel with high-resolution thermal imaging from aircraft flyovers. The processed in-situ data show highly correlated patterns between temperature and salinity at the southern end of the bay where freshwater springs can be identified at low tide. Salinity values range from 1 to 2 ppt at the southern end of the bay to 30 ppt at the mouth of the bay, indicating the presence of a freshwater wedge. The data clearly show that temperature differences can be used to track the dynamics of freshwater and seawater mixing in the inner bay region. This outcome suggests that combining the tremendous spatial density and wide geographical reach of remote temperature sensing (using drones, flyovers and satellites) with ground-truthing via appropriately located in-situ sensors (temperature, salinity, chemical, and biological) can produce a much more complete and accurate picture of the water dynamics than each modality used in isolation.

Sensor Pods: Multi-Resolution Surveys from a Light Aircraft

“…Thermal imagery is utilised at the NCG for agricultural drainage studies but also for identifying submarine groundwater discharge [43] and the Tau 640 has demonstrated capability for distinguishing a temperature differential and locating freshwater entering the ocean. The Tau 640 operates continuously in frame capture video mode following a 'record' command and individual frames were extracted for georeferencing.…”

An Evaluation of Autonomous In Situ Temperature Loggers in a Coastal Region of the Eastern Mediterranean Sea for Use in the Validation of Near-Shore Satellite Sea Surface Temperature Measurements

“…The intensity of the physical (ground water discharges [3], tidal mixing [4], upwelling phenomena [5]), chemical (water quality [6], thermal plume contamination [7], ocean acidification [8], eutrophication [9]), and biological interactions (overfishing [10], habitat loss [11], and reconfiguration of communities [12]) between the coastal zone and the terrestrial environment, both from natural and anthropogenic processes, dictates the necessity of monitoring the coastal ocean. Climate change has the potential to exacerbate other anthropogenic effects on coastal waters and the recent change in sea temperature is considered as the most pervasive and severe cause of impact in coastal ecosystems worldwide [13][14][15][16].…”

Comparison of Split Window Algorithms for Retrieving Measurements of Sea Surface Temperature from MODIS Data in Near-Land Coastal Waters

“…Monitoring water quality is one of the most pressing requirements for ensuring the sustainability of these valuable and vulnerable habitats [2]. Nowadays, SST measurements of coastal waters retrieved from remote images have a wide variety of applications such as: the analysis of temperature influence over benthic organisms [1,3]; the assessment of potential aquaculture sites [4]; the detection of ground water discharge [5]; the hydrographic characterization of nearshore waters [6]; the monitoring of river plumes [7], thermal plume contaminations [8], and upwelling phenomena [9]; quantifying complex thermal environments on coral reefs [10,11]; and the study of the interactions between residual circulation, tidal mixing, and fresh influence [12]. Many of these applications have stringent accuracy requirements [1,3,4,[8][9][10][11][12].…”

“…Sea surface temperature (SST) plays a key role in life and processes in coastal waters [1][2][3][4][5][6][7][8][9][10][11][12]. Monitoring water quality is one of the most pressing requirements for ensuring the sustainability of these valuable and vulnerable habitats [2].…”