Real-Time Monitoring and Postprocessing of Thermal Infrared Video Images for Sampling and Mapping Groundwater Discharge

It is especially difficult to parse shallow soil drainage and snowmelt from true groundwater seepage by eye in wet areas.Thermal infrared (TIR) cameras are a popular method for identifying groundwater discharge zones, which differ in temperature from stream water or stream bank sediments and vegetation.Although TIR cameras can only measure the water temperature at the surface, it is much less labor-intensive for surveys covering a large spatial scale than direct observation using thermometers or fiber-optic distributed temperature sensing (FO-DTS) systems (Hare et al., 2015).For surveys of wide rivers, the spatial distributions of groundwater discharge zones Abstract Groundwater discharge along channels can affect stream discharge, chemistry, and ecological communities.Although the spatial distribution of groundwater springs along wide rivers can be investigated by areal thermal infrared (TIR) remote sensing, this technique is difficult to apply to mapping at a high spatial resolution and under riparian tree canopies.We present a real-time monitoring and postprocessing method of ground-based TIR video for determining groundwater discharge sampling points and mapping the surface water temperature.We applied this method to mapping two headwater streams in Hokkaido, Japan, in the summer.The first site was a 1.3-km-long reach underlain by Pleistocene andesite lava.Almost all of the springs were colder and had a different chemistry compared to that of the stream water, which supports the usefulness of TIR monitoring for determining groundwater discharge zones.Video postprocessing showed that cold groundwater springs were spaced every ∼100 m, and their distribution did not follow the topography.At the second site, cold and warm springs were underlain by Holocene volcanic ash.The cold springs mainly seeped from hyporheic and riparian zones downstream, while warm springs were at the footslope.Some cold springs had much higher solute concentrations than the stream and warm springs, which suggests that the water temperature is useful for inferring sources of groundwater discharge.At this site, the video postprocessing could map not only the locations of the cold springs but also the spatial heterogeneity of the stream temperature associated with groundwater inputs.

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