Spatialization of sensible heat flux over a heterogeneous landscape

Abstract

Two methods for retrieving sensible heat flux over a bare soil/wheat composite surface are compared within the framework of an experiment performed in June 1997 during the Alpilles/ReSeDA campaign in the South-East of France. The first one is based on field measurements using large aperture scintillometers. The principle of the method is first given and its application to composite surface discussed. The comparison against reference fluxes obtained from eddy correlation technique shows that scintillometryderived fluxes are overestimated by about 10%. A numerical experiment demonstrates this is induced by aggregation problems resulting both from non linearity in the relationship between structure parameter for refractive index C N 2 and sensible heat flux H, and from non uniform sensitivity of the scintillometer to C N 2 along the pathlength. The second method is based on the use of a simple surface energy balance model, SEBAL. The model is supplied with high spatial resolution remote sensing data from two airborne sensors in visible, near infrared and TIR bands. It provides maps of surface energy fluxes at a 20 m spatial sampling. A comparison against scintillometry derived fluxes (for June 9 th ) shows important discrepancies. They result from large errors in the estimation of the roughness length z 0 in the model. This demonstrates that the use of an empirical relationship based on NDVI only is inadequate for inferring this key parameter in SEBAL. 

Scintillometer-Based Turbulent Fluxes of Sensible and Latent Heat Over a Heterogeneous Land Surface – A Contribution to Litfass-2003

“…the eddy-covariance (EC) method) of eddy heat fluxes, especially when one is concerned about the representativeness of in situ tower-based flux measurements over natural (and thus heterogeneous) landscapes (Lagouarde et al, 1996(Lagouarde et al, , 2002Chehbouni et al, 2000;Beyrich et al, 2002a;Meijninger et al, 2002a,b). In most of these studies large aperture scintillometers (LAS) were used.…”

Footprint issues in scintillometry over heterogeneous landscapes

“…In this section, first a summary of the physical background of the LAS measurement is provided, described also in detail in Chehbouni et al (2000), Lagouarde et al (2002b) and Wang et al (1978), valid for the observations over a homogeneous surface. Then a review is provided on typical problems over heterogeneous surfaces, followed by a section dealing with implications for estimating fluxes from LAS observations over a heterogeneous landscape.…”

Assessment of actual evapotranspiration over a semi-arid heterogeneous land surface by means of coupled low resolution remote sensing data with energy balance model: comparison to extra Large Aperture Scintillometer measurements

“…Therefore, scintillometry techniques have emerged as one of the best tools aiming to quantify averaged fluxes over heterogeneous land surfaces (Brunsell et al, 2011). They provide average sensible heat estimates over areas comparable to those observed by satellites (Hemakumara et al, 2003;Lagouarde et al, 2002b). Scintillometry can provide sensible heat using different wavelengths, aperture sizes 130 and configurations (Meijninger et al, 2002).…”