
Ground-Penetrating Radar - peter_d_sherman
https://en.wikipedia.org/wiki/Ground-penetrating_radar
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peter_d_sherman
>"Archaeology

Ground penetrating radar survey is one method used in archaeological
geophysics. GPR can be used to detect and map subsurface archaeological
artifacts, features, and patterning.[7]

GPR depth slices showing a crypt in a historic cemetery. These planview maps
show subsurface structures at different depths. Sixty lines of data –
individually representing vertical profiles – were collected and assembled as
a 3-dimensional data array that can be horizontally "sliced" at different
depths.)

GPR depth section (profile) showing a single line of data from the survey of
the historic crypt shown above. The domed roof of the crypt can be seen
between 1 and 2.5 meters below surface.

The concept of radar is familiar to most people. With ground penetrating
radar, the radar signal – an electromagnetic pulse – is directed into the
ground (it is important to not get GPR surveys confused with electromagnetic
surveys, a recent survey of an Iron Age hillfort in Hampshire recently
revealed the discrepancies between Magnetometry, EM and GPR surveys over the
same area). Subsurface objects and stratigraphy (layering) will cause
reflections that are picked up by a receiver. The travel time of the reflected
signal indicates the depth. Data may be plotted as profiles, as planview maps
isolating specific depths, or as three-dimensional models.

GPR can be a powerful tool in favorable conditions (uniform sandy soils are
ideal). Like other geophysical methods used in archaeology (and unlike
excavation) it can locate artifacts and map features without any risk of
damaging them. Among methods used in archaeological geophysics, it is unique
both in its ability to detect some small objects at relatively great depths,
and in its ability to distinguish the depth of anomaly sources.

The principal disadvantage of GPR is that it is severely limited by less-than-
ideal environmental conditions. Fine-grained sediments (clays and silts) are
often problematic because their high electrical conductivity causes loss of
signal strength; rocky or heterogeneous sediments scatter the GPR signal,
weakening the useful signal while increasing extraneous noise."

PDS: Also, Ground-Penetrating Radar (GPR) -- is Star Trek's planetary scanners
-- just version 0.0000001... <g>

