FIG. 6. Dielectric data for quartz sand with no dielectric dispersion and moist clays showing dielectric dispersion; the real (Eq. [7a]) and imaginary (Eq. [7b]) permittivity for water without ionic conductivity are indicated for reference. The upper-left figure shows six common soil water sensors: (A) time domain reflectometer, (B) ECH₂O EC-20 probe, (C) Hydra probe, (D) Acclima time domain transmission sensor, (E) ThetaProbe, (F) CS-616. The center figure shows a cart-mounted ground penetrating radar (GPR) (courtesy, Sensors & Software, Inc., Mississauga, ON); the top-right figure is a passive microwave remote sensing radiometer mounted on a crane.