June 22, 2018
Knysna, South Africa
“we want our excavators to stay within the [quad] lines.
It’s like coloring, but with geo-spatial data.”
Tuesday was a warm day, with enormous waves rolling into the
coastline, spray torn from the high white crests, to crash relentlessly against
the rocks below. My task, week three, was to train our students as Site Techs. This
is the person responsible for checking the geo-spatial data in the database,
and making sure all electronic data (tablets, camera, ect) is backed up
multiple times to many locations (okay, three). Capturing an archaeological
site with all the marvels of modern technology is wonderful, until something goes wrong and a computer crashes,
the tablet is dropped, and a critical item is submersed in water. Every
artifact has an associated data point captured by the total stations (“guns”)
and associated with a unique barcode, so that we can go back and understand the
“big-picture” view of the site. This
method allows for precise, rapid and extensive amounts of data to be collected.
Plus, it’s fun to manipulate the spatial data.
Keller et al. The Fauna of KEH-1 (South Africa) A
Middle and Later Stone Age site: A Pilot Study. Poster presented at the 82nd
Annual Meeting of the Society for American Archaeology 2018.
The day before, a tablet crashed and “deleted” more than 400
datapoints (these were later recovered), causing some consternation and stress.
However, this was a minor blip compared to what was about to hit us. In order
to see the location of the artifact, sometimes we need to use a crosshair fixed
to paper or on the end of a rod. The correct height of the crosshair from the
ground must be entered on the gun, or we have points showing up in random
sequences across the map. If a gunner is switching between chits and rod, it
can be easy to forget to tell the computer the correct height. The day before,
one of the excavators grabbed the scanner for the wrong gun, and accidently
entered a find number as a rod height of 4 million (placing the points on the
other side of the moon!). Luckily, fixing this involves a simple
addition/subtraction, which excel preforms for us.
Once the corrections have been entered, it is time to import
everything to the map and visually check the data. This is the fun
part—manipulating the three-dimensional map. Then one of my site tech trainees
found what we thought was a rod error: points in unexcavated sediment. We then
noticed something even more problematic: all the points were shifted, not only
down, but to the right of our quads. Since our crew is not given to digging in
random squares, we had a bigger problem on our hands. "Transforming" the gun
makes the electronics think that it has moved position relative to the triangulated position. This is useful if you want to move the gun,
less so if you are marking the positions of artifacts. It took three senior
members and two trainees combing through the numbers, but eventually we
discovered the sequence of events:
- . An excavator grabbed the wrong scanner, causing the gun to take a shot (i.e. collect a datapoint).
- . The gun reset itself to an earlier position.
- . All the following data collected was based off the assumption that the gun was somewhere it wasn’t.
As my stats professor is fond of saying, electronics are
dumb, and people are smart. Once we knew what to look for, all we had to do was
more math, mostly involving subtracting the actual coordinates from the fake
ones (in the end, it required three grad students and a bottle of wine).
However cool the computer simulations are, the actual finds
are just as fascinating. Holocene shell middens are a common scene along the
coasts of south Africa. KEH-1 is no exception, with a dense and formidable
layer of shell, bone, and who knows what else resting above the earlier
deposits. (fortunately, the deposit is on a slope, so we can target the MSA/LSA
transition we’re interested in). in our third week of excavation, we delved more
deeply into the thick shell above. While our excavators were busily removing
shell, our OLS specialist was preparing and removing samples. Additionally, we
removed one of our oldest and well-placed gunning platforms, allowing us to dig
deeper. So far, the stuff we have pulled from the lowest layers is not super
exciting (mostly large chunks of rock and the occasional bits of charcoal.
Excavators become jubilant when they discover anything else), but there is the
potential for occupation layers contemporaneous with other sites in south
Africa. And under the sediment, beneath the rock, is endless potential. At least until we hit the cave floor.
