Airborne thermal remote sensing for water temperature assessment in riversand streams

Airborne remote sensing methods are needed to assess spatial patterns of st ream temperature at scales relevant to issues in water quality and fisherie s management. In this study, we developed an airborne remote sensing method to measure spatially continuous patterns of stream temperature and evaluat ed the physical factors that influence the accuracy of thermal remote sensi ng of Bowing waters. The airborne thermal infrared (TIR) system incorporate d an internally calibrated thermal imager (8-12 mum) aligned with a visible band camera in a vertically mounted, gimbaled pad attached to the undersid e of a helicopter High-resolution imagery (0.2-0.4 m) covering the entire c hannel and adjacent floodplains was recorded digitally and georeferenced in -flight along 50- to 60-km river sections ranging from 2 to 110 m in width. Radiant water temperature corresponded to kinetic water temperature (5-27 degreesC) in a range of stream environments within +/-0.5 degreesC. Longitu dinal profiles of radiant water temperature ti-om downstream to headwater r eaches provided a spatial context for assessing large-scale patterns of the rmal heterogeneity and fine-scale thermal features such as tributaries and groundwater inputs. Potential sources of error in remote measurements of st ream temperature included reflected longwave radiation, thermal boundary la yer effects at the water surface, and vertical thermal stratification. Afte r taking into account the radiative properties of the surrounding environme nt and the physical qualities of the stream, thermal remote sensing proved highly effective for examining spatial patterns of stream temperature at a resolution and extent previously unattainable through conventional methods of stream temperature measurement using in-stream data recorders. (C) 2001 Elsevier Science Inc. All rights reserved.