Date of Award
Master of Science
Brian K. Hornbuckle
Soil moisture and vegetation remote sensing measurements can be inaccurate and/or misinterpreted in the US Corn Belt, specifically when considering seasonal variation in standing vegetation. A direct crop water measurement method was employed to assist in correction of satellite measurements, specifically to SMOS and SMAP. A 433 MHz radio link was installed in a central Iowa cornfield, shortly after planting, across a distance of 50 meters, for the purpose of measuring attenuation by crop water. This experiment ran until mid grain fill, development stage R3. Vegetation water column density increased from essentially 0 at planting to just above 4 kg/m2 at R3. Received signal strength fell from -68 dBm to -86 dBm. The relationship between water column density and signal strength was significant, on the seasonal scale (p = 3.6442×10−5, r2= 0.894), with the signal dropping around 4 dBm per 1 kg/m2 increase in water column density. At the V10 stage, vegetation contained on the order of 0.5 kg/m2 more water in the morning than the afternoon. A response in received signal strength to this diurnal variation in crop water was not detected,however. The change in crop water could be too small to measure, or it may be masked out by signal noise, such as soil moisture, leaf wetness, or temperature effects on receiver efficiency. Crop water measurements by means of a radio link can monitor growth and development, and possibly scan for water stress. Crop water measurements can also assist in correcting SMAP and SMOS soil moisture measurements, which are inaccurate in the US Corn Belt, possibly due to seasonal vegetation.
Richard Jay Cirone
Cirone, Richard Jay, "UHF band attenuation through a corn canopy with crop growth" (2019). Graduate Theses and Dissertations. 16990.