Remote sensing technology on satellites is being used to create soil moisture maps which can improve the prediction of such things as heatwaves and rainfall.
To date, soil moisture levels have been measured using L-band (1.4 GHz) technology, but the current L-band satellites can only detect soil moisture in the top 5 cm of soil.
Professor Jeff Walker, a civil engineer/hydrologist from Monash University, and his team are now using P-band technology (0.75 GHz) to detect moisture content in layers of soil up to three times deeper, resulting in more useful maps.
"P-band has the potential to not just provide soil moisture for a deeper layer of soil, but to also provide a more accurate estimate for a larger portion of the continent, as it can see through the vegetation more easily than L-band,” said Walker.
The team, which includes representatives from NASA and ESA, recently launched the first phase of this important research with the installation of an automated tower that will be used to test the P-band technology in preparation for the next generation of soil moisture satellite missions.
Walker says the Earth naturally emits microwave radiation at all wavelengths proportional to its physical temperature and emissivity, and in turn the emissivity is affected by the soil moisture content through the dielectric constant contrast between water and dry soil.
Complicating factors include the roughness of the soil which enhances this emission, and any overlying vegetation which both attenuates the ground emission and contributes its own emission proportional to the water in the foliage. Importantly, the longer the wavelength the deeper the layer of soil from which emissions can be observed, the lower the impact of surface roughness, and the more transparent the vegetation layer.
Satellites orbiting the Earth can measure these naturally emitted microwave signals and in turn infer global soil moisture maps every few days. But at present there is no passive microwave satellite operating at P-band.
[Professor Jeff Walker. Photo: Monash University]