GROUND-BASED X-BAND (3-CM WAVE) RADAR BACKSCATTERING OF AGRICULTURAL CROPS .2. WHEAT, BARLEY, AND OATS - THE IMPACT OF CANOPY STRUCTURE

The ground-based, X-band radar backscattering of wheat, barley, and oats was investigated through the growing season at VV and HH polarizations, and at incidence angles from 10-degrees to 80-degrees. The VV and HH backscattering of wheat and barley decreased at all incidence angles with crop growth until it fluctuated around a stable level from grain filling to dying of the canopy. The VV backscattering of oats at low to medium angles of incidence decreased during vegetative growth and sharply increased to a steady level with the appearance of the panicles. The geometrical architecture of the crop canopy was a major factor that influenced the X-band radar backscattering of wheat, barley, and oats. Row spacing, crop variety, lodging, and ear orientation of barley had a large effect on the radar backscattering. The architecture of the canopy also influenced the impact of the soil background on the radar backscattering of the whole crop. Stubble and straw largely determined the radar backscattering of harvested fields. Because of the many complex factors that influence the canopy structure, the radar backscattering was highly variable through the years.