Advantages and Limitations of Large Aperture Scintillometry for Ground-Truthing of Sensible Heat Fluxes

State-of-the-art hydrological models describe the diurnal variation of the water cycle. Consequently they require forcing parameters related to the surface energy balance for hourly or even sub-hourly intervals. The significance of accurate and frequent input of surface fluxes of sensible and latent heat into numerical weather forecasting has also been recognized in meteorology.

The spatial scales of a grid cell in many hydrological and meteorological models vary between 100 to 10,000 m which is significantly more than the extent of footprints of ground measurements using conventional point sensors. Recent research has revealed that scintillometry might be a suitable method to overcome this limitation. Scintillometers measure fluctuations in the intensity of electromagnetic radiation propagating along a path of between 100 to 10,000 m, from which the turbulent heat fluxes representative for an area of several square kilometers can be derived.

Using Landsat thermal imagery over New Mexico, the utility of Large Aperture Scintillometers (LAS) to perform spatially representative sensible heat flux measurements for MODIS ground truthing was evaluated. By upscaling sensible heat fluxes derived using the Surface Energy Balance Algorithm for Land (SEBAL) from the Landsat scale to the 1km MODIS scale, the subpixel scale variance in the fluxes in arid and riparian areas was examined. Footprints of actual LAS measurements were computed to determine the influence of footprint model accuracy and transect location on the ability to perform accurate LAS ground-truthing at the 1km scale.