Overview of Soil Moisture Retrieval from Passive Microwave Remote Sensing

Abstract

The surface soil moisture is a quantity resulting from the water and energy exchanges at the land-surface/atmosphere interface. Measuring this variable has potential application in hydrology and meteorology. Passive microwave remote sensing techniques have great potential for providing estimates of soil moisture with good temporal repetition on a daily basis and on a regional scale (~10 km).Compared with optical and thermal-infrared sensors, although passive microwave measurements are of lower spatial resolution than optical and infrared measurements, they are less influenced by solar illumination, aerosols, and clouds, and they are responsive to different dynamic ranges of vegetation structure and biomass. Compared with active microwave sensors, the passive microwave systems include frequent coverage, low data rates, simpler data processing. However, the effects of vegetation cover, soil temperature, snow cover, topography, and soil surface roughness also play a significant role in the microwave emission from the surface. Different soil moisture retrieval approaches have been developed to account for the various parameters contributing to the surface microwave emission. In this paper, approaches for monitoring soil moisture using passive microwave remote sensing were discussed and compared, especially the retrieval approaches which will have to be used in the future operational application.