Yeah - you can do some sort of ground penetrating radar... these days, that's a
VNA and suitable antennas.
Someone here at JPL has built a CMOS ASIC that does it, but at higher
frequencies
here's a FMCW GPR designed to operate on a helicopter on Mars
https://dataverse.jpl.nasa.gov/dataset.xhtml?persistentId=doi:10.48577/jpl.L1LCBV
On Wed, 4 Mar 2026 12:17:57 -0800, Brian Beezley <k6sti@att.net> wrote:
AB7E said:
"...I'd be most interested in trying to determine how deep the
equivalent RF ground is for future modeling (because it certainly isn't
at the surface of my dry Arizona hillside)..."
Dave, the RF ground begins at the surface, but it may extend well below.
For a plane wave exciting uniform soil, ground current decays
exponentially. It decays to 37% of the surface value at the skin depth,
which is determined by ground permittivity and conductivity. By two or
three skin depths the current has decayed to an insignificant value. You
can see skin depth values for various kinds of soil at HF here:
https://k6sti.neocities.org/hfgc
The problem is that your soil is not necessarily uniform. The electrical
characteristics may change gradually or suddenly. Stratified ground has
layers of soil of different characteristics. NEC can't model that, and
ground probes measure only the surface layer:
https://k6sti.neocities.org/sg
Using a low antenna to determine ground constants below the surface is
an attractive idea. However, it has many problems. See the end of the
stratified ground writeup for a brief discussion.
Brian
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