Measurements in dry desert soils have shown significant complex resistivity (or impedivity) variations across the
frequency range from 1 kHz to 1 MHz. The impedivity of various soils are measured in-situ in field experiments
using a custom apparatus, consisting of a probe head and accompanying custom electronics. Four galvanic
electrodes are fixed in the probe head, and arranged in a Wenner array, such that the geometric factor is
1.00 m. In this way, impedance measurements (in Ω) are easily converted to estimates of impedivity (in Ω · m).
Field measurements made in-situ are important for obtaining accurate results, because impedance measurements
typically change value significantly once soil samples are extracted from their natural environment. These changes
are due to changes in the grain boundaries, as well as changes in moisture, temperature, etc. Soil impedivity
signatures collected on a variety of soils in the south west region of the USA over the frequency band up to 1
MHz are presented.