Case Study
Mission San Antonio de Padua
Electrical Resistance Survey
See also: Summary
page - Ground Penetrating Radar Survey
- Magnetic Field Gradient Survey
Download
data plot as .PDF file (zipped)
- Highlighted in red are linear high resistance anomalies thought
to represent stone foundations of adobe walls. The long linear
anomaly running east-west across the image is thought to represent
the inner (closer to the interior plaza) wall. This anomaly may
in fact represent two paired linear anomalies that are parallel
and separated by approximately one meter.
- Solid yellow lines trace well-defined linear low resistance
anomalies interpreted to represent the remains of adobe walls.
- Dashed yellow lines trace less-well defined linear low resistance
anomalies interpreted to represent the remains of adobe walls.
- Outlined by solid yellow lines are three high resistance anomalies
that appear to occur within room blocks. These high resistance
anomalies may represent the remains of tiled room floors. Tiled
floors were discovered in the excavation block immediately adjacent
to the west.
- A dashed green line traces a linear low resistance anomaly that
is thought to represent a modern pipeline.
- Dashed blue lines bound a modern gravel access road.
General comments: Lighter areas within and around the remains of
the structure most likely represent a soil matrix composed largely
of "melted" adobe. The relative resistance of soil containing
melted adobe appears to be significantly lower than the natural
surrounding soil, although this can not be stated for certain due
to the relatively small survey area. Stone foundations underlying
adobe walls are presumably composed of higher resistance material
than the surrounding soil. Some resistance readings were likely
taken over low resistance "melted" adobe soil that had
underlying high resistance stone foundations. Whether the resulting
reading will be relatively high or relatively low is difficult to
determine. This is because the recorded signal during an electrical
resistance survey is a volume average of all material within a semi-spherical
radius equal to the spacing of the current and potential probes
(0.50 m is this case). Some low resistance anomalies interpreted
as adobe walls may possess stone foundations. The explanation for
this apparent contradiction is that the low resistance adobe component
may contribute more to the volume average than the underlying stone
component.
