Abstract
Abstract. The present paper proposes a method for the evaluation of soil evaporation, using soil moisture estimations based on radar satellite measurements. We present firstly an approach for the estimation and monitoring of soil moisture in a semi-arid region in North Africa, using ENVISAT ASAR images, over two types of vegetation covers. The first mapping process is dedicated solely to the monitoring of moisture variability related to rainfall events, over areas in the "non-irrigated olive tree" class of land use. The developed approach is based on a simple linear relationship between soil moisture and the backscattered radar signal normalised at a reference incidence angle. The second process is proposed over wheat fields, using an analysis of moisture variability due to both rainfall and irrigation. A semi-empirical model, based on the water-cloud model for vegetation correction, is used to retrieve soil moisture from the radar signal. Moisture mapping is carried out over wheat fields, showing high variability between irrigated and non-irrigated wheat covers. This analysis is based on a large database, including both ENVISAT ASAR and simultaneously acquired ground-truth measurements (moisture, vegetation, roughness), during the 2008–2009 vegetation cycle. Finally, a semi-empirical approach is proposed in order to relate surface moisture to the difference between soil evaporation and the climate demand, as defined by the potential evaporation. Mapping of the soil evaporation is proposed.
Highlights
Soil moisture is a key parameter, influencing the manner in which rainwater is shared between the phenomena of evapotranspiration, infiltration and runoff (Engman, 1991; Beven and Fisher, 1996; Koster et al, 2004)
The present paper proposes a method for the evaluation of soil evaporation, using soil moisture estimations based on radar satellite measurements
Soil evaporation estimations are essential in these regions, which are generally characterised by a dispersed vegetation cover associated with a strong contribution to the surface flux, following rainfall events in particular
Summary
Soil moisture is a key parameter, influencing the manner in which rainwater is shared between the phenomena of evapotranspiration, infiltration and runoff (Engman, 1991; Beven and Fisher, 1996; Koster et al, 2004). In the case of the land surface models, for example, the soil surface moisture is often considered to be the upper boundary condition (Bernard et al, 1986; Saux-Picart et al, 2009). These models require different parameterisations, and in particular the hydraulic conductivity or diffusivity between the surface and deeper layers. For the purposes of surface soil moisture estimation, we used the IS1, IS2, IS3 configurations, corresponding to low incidence angles of less than 30◦ The aim of this approach was to limit the influence of vegetation and soil roughness, thereby increasing the accuracy of the moisture estimations. The radar signal could be modelled with a linear relationship between radar signal and moisture, as: σt0otal ≈ α (veg) × Mv + g (Roughness, veg)
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