Sensitivity of Displaced-Beam Scintillometer Measurements of Area-Average Heat Fluxes to Uncertainties in Topographic Heights

TL;DR

This paper analyzes how uncertainties in topographic measurements affect the accuracy of heat flux estimates from displaced-beam scintillometers, emphasizing the importance of precise topography data near the beam center and at lower elevations.

Contribution

It extends previous flat terrain sensitivity analyses to variable topography, providing a method to identify critical areas for topographic measurement accuracy.

Findings

Sensitivity is highest near the beam center and close to the ground.

Precise topographic measurements in critical areas reduce uncertainty.

Topography uncertainties significantly impact heat flux estimates.

Abstract

Displaced-beam scintillometer measurements of the turbulence inner-scale length $l_o$ and refractive index structure function $C_n^2$ resolve area-average turbulent fluxes of heat and momentum through the Monin-Obukhov similarity equations. Sensitivity studies have been produced for the use of displaced-beam scintillometers over flat terrain. Many real field sites feature variable topography. We develop here an analysis of the sensitivity of displaced-beam scintillometer derived sensible heat fluxes to uncertainties in spacially distributed topographic measurements. Sensitivity is shown to be concentrated in areas near the center of the beam and where the underlying topography is closest to the beam height. Uncertainty may be decreased by taking precise topographic measurements in these areas.