Mapping Effigy Mounds with Lidar

Continental Mapping worked with the National Park Service’s Midwest Archaeological Center (MWAC) on a high resolution Lidar mapping project at the Effigy Mounds National Monument on the Mississippi River near Harper’s Ferry, Iowa. The focus area was the Sny Magill Effigy Mound Group, an area containing over 100 conical and effigy mounds dating to the Woodland period (1000 BC to 1000 AD). Numerically, it is the largest surviving group of prehistoric mounds in the United States.

A goal of the project was to assess the utility of lidar technology for assessing archeologically sensitive sites. Continental Mapping provided MWAC with a high density lidar collect, supplemental ground control, and stereo aerial imagery with a full AT solution for data verification. Lidar data was collected at dense post spacing and stereo imagery was used to verify the Lidar data accuracy.

Data visualization techniques were used to highlight different characteristics of the mound group. These visualizations, combined with ancillary GIS data sources, provided MWAC with information that helped identify previously undocumented mounds and gave insight into mound construction. Subsequent field verification confirmed many of these new finds.

The Sny Magill mound group

Note: The chalking of mounds in this oblique image provided by MWAC.

The Sny Magill mound group is heavily forested, providing a project challenge.

Shallow depressions around mounds (darker brown areas above) suggest barrow areas for mound construction or maintenance.

Anomalies in the data were field-verified by MWAC before being documented as a previously unrecorded mound.

This previously unrecorded mound remnant is barely visible on the ground and appears to be all that remains of a larger mound affected by bank erosion.

The mound group is visible in the center of this image, which shows the bare earth model of the entire project.

Project Specifications

· One square mile area near Harper’s Ferry, Iowa

· Average point spacing of 0.5 meters

· Vertical accuracy for bare earth data of 15 cm RMSE

· Horizontal accuracy of 0.5 meters RMSE

Product quality for bare earth data

· 95% of artifacts removed

· 98% of outliers removed

· 97% of vegetation removed

100 years ago the National Park Service was founded — This calls for a celebration.

Continental Mapping will be celebrating #NPS100 all year long.

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