Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Master → Pays Bas → Comparative Analysis Among Near-Operational Evapotranspiration Products for the Nile Basin Based on Earth Observations

Delft University of Technology (2014)

Comparative Analysis Among Near-Operational Evapotranspiration Products for the Nile Basin Based on Earth Observations

Hofste, R.W.

Titre : Comparative Analysis Among Near-Operational Evapotranspiration Products for the Nile Basin Based on Earth Observations

Auteur : Hofste, R.W.

Université de soutenance : Delft University of Technology (TU Delft)

Grade : Master Thesis 2014

Résumé
Following the success of open access rainfall products based on earth observation data, similar global products are now under development for actual evapotranspiration. In this research, seven prototype evapotranspiration products based on MODIS and geostationary satellites were compared for the Nile basin. They include the special MOD16 version of the Nile basin, SEBS, SSEBSop, ALEXI, GLEAM, LSA-SAF and CMRSET. Most datasets are not yet released, and are in their testing phase before being disseminated to a wide audience. These remotely sensed ET products are fundamentally different in their parameterizations, ranging from reference ET based fractions products to two-layer turbulent transfer schemes for sensible and latent heat. Furthermore the used spectral radiances vary widely from near-infrared and shortwave infrared reflectance to thermal infrared and microwaves emissions. This study covers the time span 2005 -2010 for the Nile basin. The independent validation datasets are based on flux towers and augmented with water balances of catchments and subbasins of the Nile system. Significant differences between the different evapotranspiration products are observed both on subbasin and field scale. A comparison based on land-use class shows that for some land-use classes the estimation of the varies products correspond whereas for other land-use classes the differences between the products is substantial. The different input data and different parameterization of the ET products, together with the large observed differences in ET values for certain land-classes and areas, calls for an ensemble product. A set of ET products based on different level of physics and spectral data is the necessary basis for creating an ensemble ET product. The validation reveals that using an ensemble product instead of a single remote sensing evapotranspiration product yields more reliable and consistent results when compared on a subbasin and basin level. Three ensemble products have been proposed and evaluated in this study : A mean product, an ensemble product based on land-class selection and an ensemble product based on outlier statistics. The ensemble mean product based on land-use class selection is a logical solution because it recognizes that not all ET products have an equally good performance for various land surface conditions. Although all proposed ensemble products show better results when compared to subbasin water

Présentation

Page publiée le 11 novembre 2016, mise à jour le 14 octobre 2018