Near-surface soil moisture content is a key variable in the functioning of the environment and climate system. Radar satellites map these globally and daily, providing inputs into weather forecasts and climate models. There are, however, persistent retrieval issues with those regions of the world associated with hot arid zones. These represent some of the most fragile environments on the planet, suffering from frequent droughts, environmental degradation, and societal pressures. The lack of satellite-derived data for these areas arises due to low moisture conditions that cause the radar signal to penetrate through the soil. This causes sub-surface features such as rocks to ‘contaminate’ the returned surface signal that would otherwise carry reliable information on soil moisture.
The project will develop a soil moisture retrieval scheme appropriate to arid zones, based primarily around the European Space Agency’s Sentinel-1 radar satellites. This opportunity is built upon an innovative new model which describes the physics of the radar-soil interaction at low moisture conditions. This model requires further development and testing, including the incorporation of soil thermal and vapour flow theory, which would also allow the use of surface temperature data from the Sentinel-3 satellite to improve the retrieval. The 4m x 1m x 0.5m soil trough within the Reading Radar Facility will be used to capture high-resolution 3D radar imagery of the interaction of a radar signal with soil in controlled and repeatable conditions. With these “microwave eyes” we will be able to directly observe the radar dynamics throughout the soil volume. The model is unique by considering both surface and sub-surface scattering, while also utilizing both the phase and amplitude behaviours of the radar signal.
The overall objective of this work is to amass knowledge from laboratory and modelling studies and apply this to the development of an internationally-important, satellite-based soil moisture product relevant to the European Union’s Earth Observation Programme and EUMETSAT. For this purpose, it is expected the student will undertake an extended visit to the Technical University of Vienna to aid development of bespoke satellite image processing chains and oversee its in-service implementation. We also envisage a visit to the University of Twente in the Netherland to work on the STEMMUS soil model.