A remote sensing surface energy balance algorithm for land (SEBAL) 1. Formulation W.G.M. Bastiaanssen a, * , M. Menenti a , R.A. Feddes b , A.A.M. Holtslag c a DLO-The Winand Staring Center for Integrated Land, Soil and Water Research, P.O. Box 125, 6700 AC Wageningen, The Netherlands b Agricultural University Wageningen, Department of Water Resources, Nieuwe Kanaal 11, 6709 PA Wageningen, The Netherlands c Royal Netherlands Meteorlogical Institute/Institute of Maritime and Atmospheric Research, P.O. Box 201, 3730 AE De Bilt, The Netherlands Abstract The major bottlenecks of existing algorithms to estimate the spatially distributed surface energy balance in composite terrain by means of remote sensing data are briefly summarised. The relationship between visible and thermal infrared spectral radiances of areas with a sufficiently large hydrological contrast (dry and wet land surface types, vegetative cover is not essential) constitute the basis for the formulation of the new Surface Energy Balance Algorithm for Land (SEBAL). The new algorithm (i) estimates the spatial variation of most essential hydro-meteorological parameters empirically, (ii) requires only field information on short wave atmospheric transmittance, surface temperature and vegetation height, (iii) does not involve numerical simulation models, (iv) calculates the fluxes independently from land cover and (v) can handle thermal infrared images at resolutions between a few meters to a few kilometers. The empirical relationships are adjusted to different geogra- phical regions and time of image acquisition. Actual satellite data is inserted in the derivation of the regression coefficients. Part 2 deals with the validation of SEBAL.  1998 Elsevier Science BV. All rights reserved. Keywords: Surface energy balance; Evaporation; Remote sensing 1. Introduction c:/autopag/out/Land surface processes are of para- mount importance for the re-distribution of moisture and heat in soil and atmosphere. The exchanges of radiative, heat and moisture fluxes affect the biosphere development and physical living conditions on earth. The thermo-dynamic equilibrium between turbulent transport processes in the atmosphere and laminar processes in the sub-surface manifests itself in the land surface energy balance, which reads as Q *  G 0 + H + lE Wm -2 ; 1 Where Q * is net radiation, G 0 is soil heat flux, H is sensible heat flux and l E is latent heat flux. The sign convention of Eq. (1) is that Q * is considered positive when radiation is directed towards the surface, while G 0 , H and l E are considered positive when directed away from the land surface. Eq. (1) neglects the energy required for photosynthesis and the heat storage in vegetation. Time integrated values of latent heat flux, l E, are important for different applications in hydrology, agronomy and meteorology. Numerical models for crop growth (e.g. Bouman et al., 1996), watersheds (e.g. Famigliette and Wood, 1994), river basins (e.g. Kite et al., 1994) and climate hydrology (e.g. Sellers et al., 1996) can contribute to an improved future planning and management of land Journal of Hydrology 212–213 (1998) 198–212 0022-1694/98/$ - see front matter  1998 Elsevier Science BV. All rights reserved. PII: S0022-1694(98)00253-4 * Corresponding author. Corresponding address. ITC, P.O. Box 6, 7500 AA Enschede, The Netherlands.