This proposal is part of a project, funded by the NERC LOCAR thematic programme, which is developing new methods of estimating evaporation at the catchment scale using numerical models. In terms of the land surface, one of the challenges lies in knowing what values to use for the model parameters that describe the vegetation. The uncertainties in these parameters manifest themselves in uncertainty in the estimates of evaporation. Three of the parameters: canopy height, the amount of leaves and the amount of the sun's energy reflected by the vegetation, can be measured using remotely sensed data. We will use airborne remotely sensed data to quantify the variability in these parameters, both across the landscape as a whole and within fields. Then we can use these measures of variability to investigate how much effect they have on the estimates of evaporation. The result will be more reliable estimates of evaporation for use in informing the balance between the supply of water to householders, industry and agriculture and its use to support the flora and fauna.