Using the Total Station Transit To Prepare the Excavation Site

Last Friday Team Paleo found themselves working in the field at a local dig site, known as the Morton Village Site, to prepare for students from Michigan State University to excavate in a few weeks. When we arrived at the archaeological site, Dr. Conner, the person in charge of the dig, handed us a satellite map with a grid, and a long pole with a mirror on top. He showed us a rectangular box sitting atop of a tripod. The box was a device called a Total Station Theodolite. When we aimed the reflector pole at it, the Total Station would bounce a laser off of the mirror. The machine measured the time it took for the laser to return, and used trigonometry to figure how far away the reflector was.

We would be using the reflector to measure out 30 meter (98 feet) squares for magnetic surveying. After trekking approximately 30 meters through knee-deep grass, the team received information from Dr. Conner over a small radio, telling us how far we needed to move to get to the right spot. Finding the exact location to place a stake usually went something like this: * Static * “...Move it 1.6 meters towards me...”  * Static * “...6 inches to your left...” * More static * “...That looks good... Move it right 4 inches...” * Static * “...Go south 15 meters...” We would move back 15 meters and repeat the process all over again.

Several hours passed, and finally our work was complete. We returned with the reflector, where Dr. Conner informed us that in the next few weeks, the folks in charge of the survey would arrive with a magnetometer and scan the squares we laid out. A magnetometer scans the ground to detect minor differences in the magnetic properties of the soil. Dr. Conner invited us back to help with the survey. We all agreed, and are eager to try our luck with another expensive machine.

Total Station Transit

Reflector

More Information on the Total Station Transit 

A Total Station, which we used to determine the location of our dig site, is designed to measure the distance and angle between itself and another point. It starts by sending an electric laser to a reflector. When the beam returns from the reflector, the transit measures the return time and uses trigonometry to calculate the distance from the reflector. A grid, established in the 1980s at the Morton excavation site, allows us to pinpoint the coordinates of the point we want to find. Using the original grid as a starting point, a handheld computer calculates the coordinates so that we don't have to figure it in our heads.

We used a GIS, or Geographic Information System, to map information about the site. The GIS also stores coordinates for past excavations, allowing us to refer to them. Team Paleo identified new excavation areas we wanted to survey and then we placed the coordinates of the 30 x 30 meter blocks into the GIS. Then the information was transferred to the handheld computer. The computer signals the Total Station transit to find the first set of coordinates, and the transit calculates the angle and distance of the location. When the person manning the transit aims it in the given direction, the person in the field with the reflector lines up with the transit. They move back and forth until they find the coordinates indicated. In the last satisfying moment, an indicator stake is placed at the final coordinate.

Articles written by Gwen McDaniel