HR: 09:10h
AN: H31A-03 INVITED     [Abstracts]
TI: Estimation of Surface Evaporation Based on Assimilation of Sequential Images of Remotely Sensed Land Surface Temperature
AU: * Caparrini, F
EM: fcapa@dicea.unifi.it
AF: Dipartimento di Ingegneria Civile - Universita' degli Studi di Firenze, via S. Marta, 3, Firenze, 50139 Italy
AU: Entekhabi, D
EM: darae@mit.edu
AF: Department of Civil and Environmental Engineering, Massachustts Institute of Technology, 77 massachusetts avenue, Cambridge, MA 02139 United States
AU: Castelli, F
EM: fabio@dicea.unifi.it
AF: Dipartimento di Ingegneria Civile - Universita' degli Studi di Firenze, via S. Marta, 3, Firenze, 50139 Italy
AB: Evapotranspiration does not have a unique signature that can be detected by remotely deployed instruments. In order to retrieve the fluxes, the measurements need to be merged into models that infer fluxes from their space and time patterns. We here discuss an approach based on variational assimilation of Land Surface Temperature (LST) into a surface energy balance model. It does not require empirical relations such as those relating evaporation to vegetation indices (or LST) nor does it require closure assumptions such as those that assume ground heat flux is a given fraction of net radiation. There are two major unknown parameters in the estimation of evapotranspiration (near-surface air turbulent conductivity and evaporative fraction) when following an energy-balance criteria. The air turbulent conductivity scales the magnitude of the turbulent fluxes and the evaporative fraction partitions the total turbulent flux into latent and sensible heat fluxes. Both are non-dimensional parameters and uncertainties about the values drive the errors in the calculation of turbulent fluxes. The mapping capability comes from the use of land surface temperature sensed from several environmental satellites. The data may relate to different times of day and apply at different and often overlapping resolutions. Thus the assimilation system has to be multiscale and capable of constraining the estimation at varying resolutions. The surface composition can be treated either as a `combined' soil-vegetation medium, or with a `two-source' formulation where the contributions from the canopy and the exposed soil surface are singled out. A number of applications are discussed, which demonstrate the robustness with respect to environmental and satellite availability conditions. These include an application on the Southern Great Plains site using a combination of three different LST sources (where hourly evapotranspiration is mapped with a resolution of the order of few kilometers) over large continental area and a case study in a Mediterranean small watershed using data with high refresh rate from the geostationary MSG. In the framework of the latter application, the potential for using the retrieval approach in combination with a high resolution (tens to hundreds meters) distributed hydrological model is also discussed.
DE: 1818 Evapotranspiration
DE: 1833 Hydroclimatology
DE: 1836 Hydrologic budget (1655)
DE: 1854 Precipitation (3354)
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2005 Joint Assembly