A standard Ku-band FM-CW scatterometer which can transmit in the horizontal (H) and vertical (V) states was converted to a full 'Stokes Parameters' polarimeter. The system was used to evaluate the polarization response of three cereal crops (spring wheat, durum wheat, and barley), canola and fallow fields. It was found that all the targets caused partial unpolarization (a decrease in the polarization ratio) of the transmitted state but no depolarization in that the polarized portion of the received signal had the same linear polarization as the transmitted state (H or V). As a consequence, one can recover all the polarization information about these targets from the standard scatterometer measurements. This can be stated as the 'Scatterometer Polarization Theorem', in which the co-polar scatterometer components (HH or VV) contain all the polarized power plus half the unpolarized power, while the cross-polar components (HV or VH) contain exactly half of the unpolarized power. There was more attenuation by wheat of V than H transmissions. This indicates that, for the V transmit state, the polarized component of the signal is anti-correlated with the plant water content. For canola, a randomly structured target medium, the unpolarized component of the signal correlates positively with plant moisture.