Use of Thermal Infrared Imagery to Complement Monitoring and Modeling of Spatial Stream Temperatures

Thermal infrared (TIR) surveys are effective methods to map surface spatial temperature patterns along a river. We used two data sets of TIR-derived longitudinal temperature profiles to analyze reach-scale spatial patterns of thermal heterogeneity of the Wenatchee River, in the Pacific Northwest region of the United States as part of a temperature total daily maximum load investigation. The TIR data indicate that the river has a general downstream heating trend; the magnitudes, reach variability, and longitudinal gradients are influenced by the headwater conditions, channel morphology, tributary locations, flow rates, and weather. Detailed TIR images facilitate identifying regions with high local thermal heterogeneity where we recommend a weighted average approach to estimate local spatial average temperature using temperatures from pixels of the thermally distinctive areas rather than using the temperature extracted from pixels sampled along the central part of the channel. TIR-derived daily maximum temperatures complement monitoring and modeling of spatial stream temperatures.