• thermal infrared;
  • saturated area connectivity;
  • variable active area;
  • variable contributing area


The hillslope-riparian-stream system is a key functional unit of catchments, yet very difficult to measure and monitor due to its tremendous complexity and high spatio-temporal variability. Here, we present a simple and practical tool for imaging directly these hillslope-riparian-area connections. We used a FLIR b50 infrared camera to produce thermal images at the scale of 140 × 140 pixels over the spectral range 7·5–13 µm. Our IR imaging technique is sensitive to the upper 0·1 mm of the water column. Images were obtained from a constant position on the right bank of the Weierbach catchment in Luxembourg, at an incidence angle of approximately 45° over a 5-week period. The study site measured 5 × 3 m. Our results show that ground-based IR imagery can discriminate between areas with snow cover, snow melt, soil seepage, and stream water. More importantly, it can detect when and where variably saturated areas are active and when connectivity exists between the hillslope–riparian–stream system. Our proof of concept suggests that this is a simple, inexpensive technology for sequential mapping and characterisation of surface saturated areas and a useful complement to conventional tracer techniques. Copyright © 2010 John Wiley & Sons, Ltd.