Ground-Based Thermal Imaging of Stream Surface Temperatures: Technique and Evaluation

Abstract

We evaluated a ground-based handheld thermal imaging system for measuring water temperatures using data from eight southwestern USA streams and rivers. We found handheld thermal imagers could provide considerably more spatial information on water temperature (for our unit one image = 19,600 individual temperature measurements) than traditional methods could supply without a prohibitive amount of effort. Furthermore, they could provide measurements of stream surface temperature almost instantaneously compared with most traditional handheld thermometers (e.g., >20 s/reading). Spatial temperature analysis is important for measurement of subtle temperature differences across waterways, and identification of warm and cold groundwater inputs. Handheld thermal imaging is less expensive and equipment intensive than airborne thermal imaging methods and is useful under riparian canopies. Disadvantages of handheld thermal imagers include their current higher expense than thermometers, their susceptibility to interference when used incorrectly, and their slightly lower accuracy than traditional temperature measurement methods. Thermal imagers can only measure surface temperature, but this usually corresponds to subsurface temperatures in well-mixed streams and rivers. Using thermal imaging in select applications, such as where spatial investigations of water temperature are needed, or in conjunction with stationary temperature data loggers or handheld electronic or liquid-in-glass thermometers to characterize stream temperatures by both time and space, could provide valuable information on stream temperature dynamics. These tools will become increasingly important to fisheries biologists as costs continue to decline.

Received October 3, 2014; accepted September 3, 2015

ACKNOWLEDGMENTS

We thank Julie Meka Carter, Mike Lopez, and Kelly Meyer (Arizona Game and Fish Department); Amy Unthank (U.S. Forest Service); Stewart Jacks and Jeremy Voeltz (U.S. Fish and Wildlife Service); and David Ward and William Persons (U.S. Geological Survey) for project consultation and review. We thank Ann Bonar, Sophia Bonar, Sonja Bonar, Stephani Clark Barkalow, Morgan Brizendine, David Ward, and William Persons for assistance in the field. This project was funded by the U.S. Geological Survey Arizona Cooperative Fish and Wildlife Research Unit. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.