Archaeological Geophysics Methodology
Sub-surface imaging by means of geophysical survey is a powerful tool for archaeological site assessment and mapping which historically has been under-utilized in North American archaeology. Continuing improvements in survey equipment performance and automation have made large area surveys with a high data sample density possible. Advances in processing and imaging software have made it possible to detect, display, and interpret subtle patterns of cultural origin within the geophysical data.
Some of the unique advantages of geophysical survey:
- Geophysical methods are non-intrusive, and are not destructive to site integrity
- A survey can provide detailed evidence of occupation and activity not visible from surface information
- Large areas mapped quickly and inexpensively
- A subsurface map of a site can be created before excavation is begun
- Researchers can assess site patterning and integrity, and target specific cultural features for excavation while avoiding others
Geophysical data can complement excavation data, and allow researchers to understand excavation results within the entire site context A survey must be a joint endeavor between the archaeologist and the surveyor. The suitability of a site for survey, a definition of the archaeological record, its stratigraphy and geophysical contrast as well as survey design must all be determined jointly. Competent cultural interpretation of the geophysical data is clearly a multi-disciplinary activity.
Square-array electrical resistance survey
Electrical resistance map of historic features at the Army City site
Surveys which are both successful and cost-effective must satisfy a number of basic requirements. They must be implemented using appropriate and properly configured survey equipment. The data sampling strategy and density must be matched to the spatial resolution and statistical requirements of the survey. Monitoring the quality of data while in the field is mandatory, and post survey data processing must be both appropriate and mathematically sound.
Archaeo-Physics personnel have academic and professional backgrounds in archaeology, electrical engineering, electromagnetic theory and civil engineering. We have 40 years combined experience providing professional geophysical surveys specifically to the archaeological community. Our staff also has many years of archaeological field experience including all phases of cultural resource management and academic research projects.
Our principal survey tools are:
- Geoscan Research RM 15 electrical resistance meter
- Geoscan Research FM 256 magnetic gradiometer
- Geoplot 3.0 analysis and interpretation software.
- PulseEKKO 1000 ground penetrating radar
As may be appropriate we also use:
- G858 portable cesium magnetometer/gradiometer
- EMP400 electromagnetic conductivity/magnetic susceptibility meter
- EM38 electromagnetic conductivity/magnetic susceptibility meter
- EM31 electromagnetic conductivity meter
In addition to field surveys, we may also perform laboratory analysis of soils and other materials. This may be done before survey in order to assess feasibility and optimize survey design. Laboratory testing may also be useful for post-survey and post-excavation analysis.
Post-survey support includes collaboration in ongoiong interpretation and guidance in "invasive" explorations. Our staff has extensive excavation experience as well as insight into the geophysical expression of archaeological patterning. We endeavor to provide guidance that make will testing and data recovery economical and efficient as possible. In many circumstances, preliminary results can be made available in the field, and testing or formal excavation may conducted concurrently with the survey.
A technical report describing our work, including high resolution maps with detailed interpretation is presented to the client upon completion of analysis. Ongoing support includes: ongoing interpretation based on teating and excavation; consultation on further fieldwork; and collaboration on conference papers and publications.