Multitemporal C- and L-band polarimetric signatures of crops

Polarimetric synthetic aperture radar (SAR) data of agricultural fields have been acquired by the Danish L- and C-band polarimetric SAR (EMISAR) in March, May, June, and July of 1995, covering the agricultural test site at the Research Centre Foulum located in Central Jutland, Denmark. Polarimetric signatures for a number of agricultural crops, including both spring and winter crops, have been analyzed, both with respect to incidence angle variations, between-field differences, and multitemporal variations for the individual crops. The variation with incidence angle was most pronounced for the early acquisitions (March and May) where the backscatter was dominated by surface scattering. In later acquisitions (June and July), the variation was relatively small except for a few cases. Also, the largest between-field variation was observed for the early acquisitions, probably due to the sensitivity of the polarimetric parameters to differences in plowing and planting direction, soil texture, tillage practice, time of planting, etc. The analysis of the multitemporal signatures revealed significant information about the scattering mechanisms. Especially, the correlation coefficient between HH and VV showed a large difference between spring and winter crops in the beginning of the growing season, because of the dominance of surface scattering for spring crops and volume scattering for winter crops.