Impact of Using Different Time-Averaged Inputs for Estimating Sensible Heat Flux of Riparian Vegetation Using Radiometric Surface Temperature

Abstract

A riparian corridor along the Rio Grande dominated by the Eurasian tamarisk or salt cedar (Tamarix spp.) is being studied to determine water and energy exchange rates using eddy covariance instrumentation mounted on a 12-m tower. The potential of using remotely sensed data to extrapolate these local estimates of the heat fluxes to large sections of the Rio Grande basin is under investigation. In particular, remotely sensed (radiometric) surface temperature can be used to estimate partitioning of net radiation energy into sensible and latent heat fluxes from vegetated landscapes. An important issue that has not been addressed adequately in the application of radiometric surface temperature data is the effect of using different time-averaged quantities in heat transfer formulations. This study evaluates the impact on sensible heat flux estimation of using relatively short time-averaged (1 min) canopy temperatures measured from a fixed-head infrared radiometer with 1-, 10-, and 30-min time-averaged micrometeorological input data used in estimating the resistance to heat transfer. The results indicate that, with short time-averaged radiometric surface temperatures (essentially ?instantaneous? from a satellite), variations in sensible heat flux strongly correlate to fluctuations in net radiation conditions. Under near-constant net radiation input, natural perturbations in surface temperature also contribute to variations in sensible heat flux but are typically an order of magnitude smaller. The resulting implications for computed heat flux estimates using data from remotely sensing platforms and validation with flux tower measurements along riparian corridors are discussed.