Radiobrightness thermal inertia sensing of soil and canopy moistures for grassland areas

Radiobrightness thermal inertia (RTI) can be used to estimate the moisture content of prairie grassland and agricultural soils. Moisture increases the apparent thermal inertia' of soil by increasing its thermal conductivity, density, and specific heat. Apparent thermal inertia is further increased by evapotranspiration during the day and by condensation at night. Increasing moisture content causes a decrease in microwave emissivity. Combined, these effects should enhance the dependence of RTI upon soil moisture. 37 GHz data from the Nimbus 7 SMMR have been used to demonstrate the plausibility of the RTI method. However, longer data sets over several contiguous days of moisture change were needed to more fully test the model. Also, the masking effect of a vegetation canopy is best handled through the use of a Soil Vegetation-Atmosphere Transfer (SVAT) model. From August 19 to September 8, 1992, the authors' Tower Mounted Radiometer System (TMRS) was operated at the Matthaei Botanical Gardens, Michigan. 19, 35, 37.0, and 85.5 GHz polarimetric observations were made. Simultaneous measurements of solar and net downwelling radiation, air temperature, precipitation, relative humidity, thermal IR surface temperature, wind speed, subsurface temperature, and soil heat flux were also made.<>