Comparison of Three in Situ Surface Soil Moisture Measurements And Application to C-Band Scatterometer Calibration

C-band scatterometers can be used to measure the surface soil moisture. This technique does not directly give the water content and a signal calibration is necessary. This is done by comparing the scatterometer signal (expressed as a scattering cross section per unit area) to gravimetric samples. The gravimetric sample calibration takes a lot of time and people, hence it is not adapted to airborne or satellite remote-sensing measurements. In this paper, new automatic equipment based on the measurement of the real part of the complex permittivity of moist soil is presented. The results of a one-month experiment show that this technique is well adapted to the automatic monitoring of soil moisture in general. In particular, it can be used for the calibration of microwave remote-sensing equipment.