Mapping Microwave Penetration Depths Over Arid Areas

Passive microwave remotely sensed data are increasingly used for the estimation of earth system parameters with application for precision agriculture or meteorology. They are almost impervious to clouds and can be used to provide long term global observations of Earth surface temperatures, soil moisture, etc. However the effective sampling depth of the soil is not constant and this leads to dubious results over arid areas. To account for this phenomenon, in this study we analyse the relationship between the soil geological characteristics such as porosity, sand/clay/silt fractions, and its thermal and electrical properties. Indeed the brightness temperatures measured at different frequencies depend on the effective temperature and emissivity that is a related to the sampling depth and the soil temperature profile. The soil temperature profile can be estimated based on the diffusion equation that relies on the thermal properties of the soil, and the microwave sampling depth is related to the dielectric permittivity of the material. The early results shown here show how we can use soil characteristics maps, and relate them to differences in brightness temperatures at the GMI frequencies between 10 and 89 GHz over the Sahara desert and to different penetration depths at these frequencies.