Geophysical Remote Sensing

What is geophysical remote sensing?

Archaeological remote sensing is defined as any technique that allows archaeologists to remotely study the remains of past cultures without physically contacting them – this can include aerial photography, satellite imagery, and a range of geophysical techniques.  Geophysical survey uses aspects of the earth’s physical properties to investigate archaeological features located at or near the ground surface.  Human activities such as the movement of soil and rock, building houses, the excavation of pits, and building fires can all alter the local physical properties of the soil in significant ways.  Remote sensing instruments use the associated variations in magnetic fields, the ability of soil to conduct electricity, or the ease with which an electromagnetic wave can pass through the soil to detect the traces of these human activities.

The advantage of geophysical survey is that it can examine larger areas more quickly and with greater resolution than is possible with traditional archaeological field methods. Further, geophysical methods have the advantage of being nondestructive, a capacity particularly relevant for sites where it is neither permissible nor desirable to disturb them.  These characteristics, along with advances in the instrumentation and interpretation of geophysical data have caused them to become an increasing important in archaeological research.

What type of remote sensing is conducted at Luther?

Geophysical remote sensing at Luther College currently uses three of the most prevalent instruments used for archaeological geophysical research: a Bartington Grad 601-2 fluxgate gradiometer, a Geoscan RM-85 soil resistivity meter, and GSSI SIR-4000 ground penetrating radar (GPR) system.

The Bartington gradiometer measures local variations in the earth’s magnetic field using pairs of vertically oriented sensors located 1.0 meter apart.  The Bartington instrument uses two sensor tubes to record two simultaneous lines of data, increasing the rate of data collection.  Data is collected by walking the instrument along regular traverses and readings are taken automatically at predetermined intervals. The sensors record small variations in the earth’s magnetic field (or gradient).

The Geoscan RM85 resistance meter uses arrays of probes to inject an electrical current in to the soil and measure the degree of resistance of that current passing through.  The probe array is repeatedly picked up and placed at regular intervals, and readings are automatically recorded at each location to create a larger of regular data points across an area.  The probes record the differences in resistance at these locations.

The final instrument is a GSSI SIR 4000 portable GPR system with a 400mhz antenna.  The instrument mounts the antenna and data collector on a three-wheel cart that is pushed along the traverse ropes at preselected intervals while a calibrated survey wheel records the distance along the traverse line. The 400mhz antenna transmits an electromagnetic wave into the ground and measures variations in the way that wave is reflected back to the ground surface.  

In addition to these instruments the Luther College Anthropology Lab also additional instruments and software that are integral to conducting remote sensing.  This includes a survey grade Trimble GNSS survey system with R10 and R2 GNSS receivers and TSC3 data collectors.  We also have a range of analytical software packages including Geoplot, Terrasurveyor, RADAN, Surfer, ArcMap, and Photoscan. These instruments and software represent an ideal suite of tools for investigating many of the aspects of the archaeological record in northeast Iowa including prehistoric mounds, earthworks, and village sites.

What opportunities are there for students to participate in remote sensing?

There are a range of opportunities for Luther College students to get direct, hands on experience with archaeological remote sensing in both the classroom and research settings.  Luther College is one of only a few colleges and universities in the United States that offers remote sensing opportunities specifically oriented for undergraduates.  All students in the introductory archaeology course learn about the basics of these techniques and get the opportunity to try them out as part of the course. The Anth 305 Remote Sensing in Archaeology class provides an in-depth overview of both the theory and methods of geophysical remote sensing.  Further, the archaeological field school involves a remote sensing component alongside traditional archaeological techniques.

Beyond the classroom, remote sensing represents an ideal means for students to develop and implement their own research projects . Students interested in archaeology are encouraged to develop research projects that use these techniques to explore questions associated with the archaeology of the local area.  The Luther College Dean’s Office provides funding for collaborative summer research experiences for students to work directly with faculty members on research projects in the local area.  Further, students are encouraged to develop senior research projects utilizing remote sensing.