Models for grassland and agricultural stubble on the plot scale (O 102 m2) have already been validated by our research group in several Radiobrightness and Energy Balance EXperiments (REBEXs). We are currently developing a new LSP/R model adapted specifically to field corn. Corn represents the next level of modeling for our group because the size of some canopy components (stalks and cobs) are on the order of microwave wavelengths and hence will scatter, rather than simply absorb, the radiation emitted from the soil. Data gathered during two extensive REBEXs held during the summers of 2000 and 2001, will be used to force and validate the model.
We present measurements made of near-surface soil moisture during REBEX-7 and REBEX-8 . We define near-surface soil moisture as the water content of the first few centimeters of the soil. Near-surface soil moisture is an extremely important variable in the context of this work since it is the quantity of water which a microwave radiometer can measure. Over 100 measurements of near-surface soil moisture were made daily using a hand-held impedance probe (ThetaProbe, Delta T Devices). These measurements allow us to more accurately represent the hydrologic state of the field site as compared to previous studies. The site was found to be surprisingly uniform, both in terms of the mean and variance of soil moisture measurements. Near-surface soil moisture was also recorded continuously with buried time-domain reflectometry (TDR) probes (CS-615, Campbell Scientific). Accurate calibration of these specific TDR instruments to a specific soil has been difficult to accomplish in the past. Our presentation focuses on the method we used to continuously calibrate the buried TDR instruments with the hand-held impedance probe, as well as an analysis of the near-surface soil moisture data collected during the two experiments.
Supplementary URL: http://www.eecs.umich.edu/grs