Télédétection et ressources en eau/Remote sensing and water resources
305
Models for determining evapotranspiration
RESUMÉ
L′évapotranspiration réelle peut être calculée à partir du rayonnement net journalier et de
la différence entre la température de l′air et de surface des cultures en milieu de journée.
Nous proposons d′estimer l′évapotranspiration à l’aide des modèles à une ou deux couches
et d’une combinaison d′images Landsat et NOAA, les premières pour connaître la
distribution des cultures et les deuxièmes pour déterminer la variation spatiale de la
température. Cette méthode permet d′estimer l′évapotranspiration réelle avec une marge
d’erreur de 0,9 mm par jour et, en conséquence, de contrôler les besoins d′irrigation.
ABSTRACT
The actual evapotranspiration can be calculated from daily net radiation and the
temperature difference between air and crop surface at midday. We propose estimating
actual evapotranspiration by using one or two layer models and combining Landsat and
NOAA images, the former for defining crop distribution and the latter for determining
spatial variation in temperature. This methodology allows for the estimation of actual daily
evapotranspiration with an error margin of 0.9 mm day
-1 , and in consequence to monitor
water requirements.
INTRODUCTION
Knowledge of evapotranspiration is useful for different aims like water budget calculations,
climatological and meteorological studies. In arid regions evapotranspiration is a significant and
often the dominant water flux leaving the Earth´s land surface, nearly all the inputs in the form of
rain is lost trough evapotranspiration therefore the importance of this parameter for controlling
watering schedule and determining crops productivity. We have applied this methodology to the
Barrax and Tomelloso (Spain) areas, pilot experiment zones of the EFEDA project. (Bolle and
Langer,1991)
METHODOLOGY
Attempting to determine the energy transport in sparsely vegetated rangelands requires methods
such as those proposed by Shuttleworth and Wallace (1985), Shuttleworth and Gurney (1990) or
Kustas (1990) that consider the soil and canopy as separate sources or sinks for latent and
sensible heat fluxes.
E. Hurtado and M.M. Artigao, Department of Applied Physics, Polytechnical College of
Albacete, University of Castilla-La Mancha, Albacete, and V. Caselles, Department of
Thermodynamics, Faculty of Physics, University of Valencia, Burjassot, Spain
305
Models for determining evapotranspiration
RESUMÉ
L′évapotranspiration réelle peut être calculée à partir du rayonnement net journalier et de
la différence entre la température de l′air et de surface des cultures en milieu de journée.
Nous proposons d′estimer l′évapotranspiration à l’aide des modèles à une ou deux couches
et d’une combinaison d′images Landsat et NOAA, les premières pour connaître la
distribution des cultures et les deuxièmes pour déterminer la variation spatiale de la
température. Cette méthode permet d′estimer l′évapotranspiration réelle avec une marge
d’erreur de 0,9 mm par jour et, en conséquence, de contrôler les besoins d′irrigation.
ABSTRACT
The actual evapotranspiration can be calculated from daily net radiation and the
temperature difference between air and crop surface at midday. We propose estimating
actual evapotranspiration by using one or two layer models and combining Landsat and
NOAA images, the former for defining crop distribution and the latter for determining
spatial variation in temperature. This methodology allows for the estimation of actual daily
evapotranspiration with an error margin of 0.9 mm day
-1 , and in consequence to monitor
water requirements.
INTRODUCTION
Knowledge of evapotranspiration is useful for different aims like water budget calculations,
climatological and meteorological studies. In arid regions evapotranspiration is a significant and
often the dominant water flux leaving the Earth´s land surface, nearly all the inputs in the form of
rain is lost trough evapotranspiration therefore the importance of this parameter for controlling
watering schedule and determining crops productivity. We have applied this methodology to the
Barrax and Tomelloso (Spain) areas, pilot experiment zones of the EFEDA project. (Bolle and
Langer,1991)
METHODOLOGY
Attempting to determine the energy transport in sparsely vegetated rangelands requires methods
such as those proposed by Shuttleworth and Wallace (1985), Shuttleworth and Gurney (1990) or
Kustas (1990) that consider the soil and canopy as separate sources or sinks for latent and
sensible heat fluxes.
E. Hurtado and M.M. Artigao, Department of Applied Physics, Polytechnical College of
Albacete, University of Castilla-La Mancha, Albacete, and V. Caselles, Department of
Thermodynamics, Faculty of Physics, University of Valencia, Burjassot, Spain