Ground-penetrating radar is used to map physical and chemical contrasts in the materials below the ground’s surface. Contrasts of interest to cultural resource managers include building foundations and basements, trenches, prehistoric structures, middens, unmarked burials, anthropogenic soil surfaces, and any case where a change in the physical or chemical properties of the subsurface are present.
To collect GPR data, pulses of electromagnetic energy are transmitted into the ground where they reflect off of changes in the sub-surface material and are collected by a receiving antenna. The amplitude strength of the received electromagnetic pulse and its elapsed travel time are measured and collected by a computer. Elapsed travel time is used as a proxy for distance and can be converted to distance through velocity calculations. Data points are collected in transects with as many as 50 pulses of electromagnetic energy being transmitted and received for each meter. Together all of the pulses form a profile. Multiple parallel transects are lined up in a grid and the space between each transect is interpolated to form a three-dimensional block of data. This block of data can be sliced at arbitrary depths for plan view interpretation of GPR results.
Ground-penetrating radar survey is well-suited to both historic and prehistoric sites. New South Associates has had success using GPR at historic cemeteries to locate unmarked burials, on prehistoric and historic structures, to map Civil War era trenches, and many more types of sites. This is the only geophysical method that allows for accurate depth estimates. Data collection requires the antenna to have contact with the ground surface at all times. It might not be suited to project locations with heavy vegetation (that cannot be cleared) or very extreme topography. GPR does work very well through paving, gravel, grass, and any relatively unobstructed surface. New South Associates uses a GSSI SIR 3000 control unit and selects antenna frequencies in consultation with client needs and project goals; our most common antenna frequencies for archaeological use are 400 MHz, 900 MHz, and 200 MHz. New South Associates also provides geophysical training.