Tanguy, M; Baille, A; Gonzalez-Real, MM; Lloyd, C; Cappelaere, B; Kergoat, L; Cohard, JM (2012). A new parameterisation scheme of ground heat flux for land surface flux retrieval from remote sensing information. JOURNAL OF HYDROLOGY, 454, 113-122.
The objective of the study was to assess the performance of a new parameterisation scheme of ground heat flux (G) for retrieving surface fluxes from remote sensing data (MODIS-Terra). Formulae that are based on empirical relationships relating G to net radiation, R-n (G = alpha R-n, alpha being a function of a vegetation index, VI) are currently used, but presented drawbacks, especially in bare or sparse vegetation areas because of the poor adequacy of VI-based relationships to account for changes in soil moisture. In this study, we proposed to link a to the evaporative fraction, EF. In a first step, using a non-dimensional form of the surface energy balance, we demonstrated that a is functionally related to EF and to the ratio gamma = G/H (H = sensible heat flux). In a second step, we proposed an EF-based parameterisation of alpha, using ground fluxes data sets collected throughout the years 2005, 2006 and 2007 at four flux-tower sites in West African countries (Mali, Benin, Niger) that differ in surface conditions and Monsoon influence. The analysis indicated that the average site-specific values of alpha and EF were well described by a linear relationship of the type alpha = a EF + b, with a = -0.22 and b = 0.23. In a third stage, we investigated whether ET-retrieval from remote sensing information (MODIS-Terra) using the new parameterisation of alpha perform better than the classical formulation through VI-based relationships. We found that the retrieved values of H using the new parameterisation supplied the best agreement with the observed ground data and significant improvement with respect to estimates from alpha-VI relationships. Advantages and limitations of the proposed parameterisation scheme were discussed. (C) 2012 Elsevier B.V. All rights reserved.