Soil moisture retrieval from ERS scatterometer data

Abstract

Soil moisture is an important component of the hydrological cycle. It is a limiting factor in agricultural production, puts an important control on ecosystems, influences runoff, affects weather patterns, and is a crucial element in climate change studies. The objective of this work was to develop a method to retrieve soil moisture from ERS Scatterometer data. The ERS Scatterometer is a spaceborne radar operated at 5.3 GHz (C- band) and has a spatial resolution of 50 km. It has been flown on the European Remote Sensing Satellites ERS-1 and ERS-2. It measures the backscattering coefficient that, over land surfaces, is a function of vegetation, surface roughness, soil moisture content and incidence angle. To estimate soil moisture the other influencing factors need to be accounted for. How this is achieved is described in this thesis. The retrieved soil wetness values are a relative measure of the moisture content in the remotely sensed soil surface layer which, in C-band, is in general 0.5 - 2 cm deep. A method to estimate the water content in the soil profile from the ERS Scatterometer and soil data is developed. A validation of the method based on an extensive data set of gravimetric soil moisture measurements from the Ukraine shows that the soil moisture content in the first meter of the soil can be estimated with a r.m.s. error of 4.9 % volumetric units. Soil moisture maps of a number of other regions with diverse climatic conditions (Mali, Iberian Peninsula, Illinois, England and Wales) were produced. A qualitative analysis suggests a good quality of the derived soil moisture maps for a wide range of climate and vegetation types.