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Development of assimilation schemes for soil moisture profiles using remotely sensed data

Research project T4/DD/09 (Research action T4)

Persons :

Description :

This proposal fits within the option "Fundamental research" for the program "Satellite observation of the Earth", subprogram "Global change", theme 'soil moisture' (A2).

The general purpose of this project is the development of algorithms to retrieve the soil moisture content in the root zone using multitemporal radar observations. Considering the complex relationships in the interaction of electromagnetic waves and the top layer of the soil, we will focus on bare soils within the framework of this project.

The algorithm will make use of a state reconstruction technique, viz. the Kalman filter. The unsaturated soil layer is considered as a dynamic system, in which the soil moisture profile represents the state vector. The one-dimensional Richards equation descripts the dynamics of this system. Both analytical and numerical solutions exist for this equation. Through radar measurements we observe for certain timesteps part of the state vector of this dynamic system. The observation equation is the mathematical expression for the observations. This equation links the state vector (or part of it) to a measured quantity (in this case the backscatter coefficient) using surface and volume scattering models. The Kalman filter makes it possible to reconstruct the state vector through the use of the system and the observation equation.

The observation model is based on the radiative transfer formulation, and has already been implemented. For drying profiles, it needs further modification, so that a sensitivity analysis on the modified version is necessary.

After implementation of both models and the Kalman filter, the technique is validated in two steps:
. The first validation is performed with a synthetic example, generated with well known accurate hydrological and observation models.
. The second validation is carried out with 3 datasets, retrieved under well-controlled conditions at the EMSL, JRC, Ispra. Italy. Accurate time series of soil moisture are available, combined with multifrequency, monostatic radar observations for 4 polarisations and 3 incidence angles.
The validation will allow to test different configurations of frequencies and polarisations. The influence of the interval between radar measurements will be closely evaluated.

A further development, not scheduled within this project, is the validation of the technique to SAR data from ERS1, ERS 2 and RADARSAT. Data concerning these sensors were acquired in previous and current projects (see form L).

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