Ground-Penetrating Radar (GPR) is a non-destructive technique. Cemeteries, shell mounds, and many other sensitive site types can be documented in detail with little or no excavation, depending on the nature of the GPR project. While GPR alone does not provide the data needed for site mitigation, GPR plan maps and profiles can enhance knowledge of site structure with great efficiency. Based on GPR findings in relation to other data sources such as probing, a strategy can be developed to limit a project’s footprint and avoid portions of a site most suitable for full preservation.
At Left: Stone foundation blocks appear in 2015 GPR slice map overlying excavation schematic of a historic structure. Our GPR mapping confirmed the alignment of blocks expected based on earlier test excavations and archival research.
Archaeological projects can recognize cost savings when incorporating GPR at survey, testing and data recovery phases. In many instances site sampling for features and artifact-rich cultural strata can be more limited, involving less excavation, if GPR is used to identify key areas to concentrate excavation units within a site. GPR does not take the place of shovel probes or test units that may be needed to recover artifacts and expose features for sampling, but it often allows excavation unit placement to focus on features and artifact concentrations that can otherwise require extensive probing to identify.
Above: GPR profile and corresponding excavation profile at Stege mound, Richmond, California. Detailed shell mound strata are evident as planar radar reflections, and disturbed pit fill is clearly differentiated from intact stratigraphy. Excavation profile courtesy of Alta Archaeological Consulting. This demonstrates that even without excavation the sequence of oblique truncated mound layers can be mapped. Similar mound strata are evident at other west coast shell mound sites we have surveyed where no excavation has taken place.
How is GPR incorporated into an archaeological project?
GPR surveys focus on a variety of buried deposits in archaeology. These include
Cultural stratigraphy/component depth and aerial extent;
Geomorphic stratum repose, composition, and conformity;
Feature type and composition;
Feature size and distribution;
Artifact concentration/dispersal;
Thermal alteration and disturbance of deposits, bioturbation etc.
At the outset of a GPR project, characteristics of a site are considered in order to determine the most suitable equipment choice and survey strategy. Context geomorphology is often key to GPR setup and interpretation. Sources include soil surveys, vegetation and hydrology mapping, geotechnical bore logs, geological mapping, and auger probing. Consideration of site taphonomy from plowing, filling, weathering, frost heave, seasonal saturation and drying, and bioturbation (rodents, worms, roots) is also useful for interpreting GPR results.
GPR surveys are never done in a vacuum. Every archaeological application of the technology involves relating GPR data to other archaeological information. The surveyor will relate GPR data to any profile and plan exposures in test unit and trench excavation, clearing excavation, and cutbanks on or near a site. Often, GPR is used at more than one phase during an excavation project, so that data interpretations can be fine-tuned with “ground truthing.” Removing overburden often allows more precise GPR feature and stratum mapping.
Radar reflections are interpreted based on known site elements from records such as historic photos, maps and drawings, textual description, and previous archaeological reports. If visible structures are partially exposed at a site their buried portions can be traced with GPR. These structures might include buildings, culverts, stone alignments, earthworks, mounds, grave markers, and other surface features. Other geophysical survey data are sometimes tied in with GPR data, including findings from magnetometer, resistivity, EM and LIDAR surveys.
for more information contact scottbyram@featuresurvey.com
GPR surveys focus on a variety of buried deposits in archaeology. These include
Cultural stratigraphy/component depth and aerial extent;
Geomorphic stratum repose, composition, and conformity;
Feature type and composition;
Feature size and distribution;
Artifact concentration/dispersal;
Thermal alteration and disturbance of deposits, bioturbation etc.
At the outset of a GPR project, characteristics of a site are considered in order to determine the most suitable equipment choice and survey strategy. Context geomorphology is often key to GPR setup and interpretation. Sources include soil surveys, vegetation and hydrology mapping, geotechnical bore logs, geological mapping, and auger probing. Consideration of site taphonomy from plowing, filling, weathering, frost heave, seasonal saturation and drying, and bioturbation (rodents, worms, roots) is also useful for interpreting GPR results.
GPR surveys are never done in a vacuum. Every archaeological application of the technology involves relating GPR data to other archaeological information. The surveyor will relate GPR data to any profile and plan exposures in test unit and trench excavation, clearing excavation, and cutbanks on or near a site. Often, GPR is used at more than one phase during an excavation project, so that data interpretations can be fine-tuned with “ground truthing.” Removing overburden often allows more precise GPR feature and stratum mapping.
Radar reflections are interpreted based on known site elements from records such as historic photos, maps and drawings, textual description, and previous archaeological reports. If visible structures are partially exposed at a site their buried portions can be traced with GPR. These structures might include buildings, culverts, stone alignments, earthworks, mounds, grave markers, and other surface features. Other geophysical survey data are sometimes tied in with GPR data, including findings from magnetometer, resistivity, EM and LIDAR surveys.
for more information contact scottbyram@featuresurvey.com