Characterization of terrestrial discharges into coastal waters with thermal imagery from a hierarchical monitoring program

Background: The hierarchical use of remotely-sensed imagery from satellites, and then proximally-sensed imagery from helicopter sand drones, can provide a range of spatial and temporal coverage that supports water quality monitoring of complex pollution scenarios. Methods: The study used hierarchical satellite-, helicopter-, and drone-acquired thermal imagery of coastal plumes ranging from 3 to 300 m, near Naples, Italy, and captured temporally- and spatially-overlapping in situ samples to correlate thermal and water quality parameters in each plume and the seawater. Results: In situ sampling determined that between-plume salinity varied by 37%, chlorophyll-a varied by 356%, dissolved oxygen varied by 81%, and turbidity varied by 232%. The radiometric temperature, Trad, for the plume area of interest had a correlation of 0.81 with salinity, 0.74 with chlorophyll-a, 0.98 with dissolved oxygen, and -0.61 with turbidity. Conclusion: This study established hierarchical use of remote and proximal thermal imagery can provide monitoring of complex coastal areas.