Case Study
Hidatsa Earth Lodges
Nightwalkers Butte, Fort Berthold Reservation, North
Dakota
Nightwalker's Butte (also known as
Duskwalker's butte) is a fortified village occupied in the late
18th century by a dissident grop of Hidatsa. An electrical resistance
survey was performed as part of an interdisciplinary archaeological
study of this site in partnership with the descendant community.
Download images as a *.PDF
file (zipped)
A highpass filter is implemented by calculating the
local mean in a moving window and subtracting the mean from the
original map data. The size of the moving window is adjustable.
In this case, a 5 meter radius is used. The result is a new map
in which the average "background" resistance of the site
has been subtracted. The mean value of the new map is zero.
Highpass filtering of resistance data offers a number
of benefits to the mapping and interpretation of resistance data.
In addition to enhancing the visibility of small low contrast features,
it also creates a resistance map with zero mean. This zero mean
map can be thought of as a resistance map containing features which
are greater than the local average (the positive values) and features
which are less than the local average resistance (the negative values).
The zero data regions correspond to areas of no resistance deviation
from "background" or local mean.
With this insight, it is convenient to interpret positive
data as features with "greater than average resistance,"
or "less than average resistance." In order to display
anomalies associated with earth lodges, the color image was plotted
from data from which negative values and extreme high outliers had
been clipped.
