By Ethan Theuerkauf, Assistant Professor at Michigan State University
and Guy Meadows, Professor at Michigan Tech. University
Part of the Great Lakes Bottom Mapping Working Group Winter 2021 Underwater Update newsletter. Subscribe here.
In the old days it took a survey crew on shore and on a boat many hours to acquire nearshore survey profiles that mapped the top of the bluff or dune to offshore beyond the depth of closure. In addition, once back in the office, much more work was required to process those data. That has now all changed.
The shore crew is now one person outfitted with a high-accuracy GPS system and a drone and the boat crew is now one person on a personal watercraft (PWC). In addition, the shore and water parts of the survey no longer need to be conducted simultaneously—they can be combined together using computer programs back in the office. Surveying with these new technologies was ten times faster than the methods used in historical surveys, which allows more frequent monitoring of larger stretches of the coast.
How does it work? The coast shoreline portion of the survey utilizes a quadcopter drone with a camera to collect a series of photographs over the study site. Throughout the site about a dozen black and white targets known as ground control points, are placed through the study area and surveyed with a GPS. These are used to turn the photos collected with the drone into centimeter-accurate 3D maps of the beach, bluff, or dune. From here, a profile can be extracted and compared to the historical data collected by Dr. Meadows since the 1980s.
The nearshore portion of the survey consists of a PWC outfitted with a high-resolution GPS/moving map display and a single beam echosounder. The offshore endpoint of the survey line is acquired and the survey is run from offshore toward the beach. The nearshore endpoint of the survey is on the beach and is a control point for both the drone and PWC surveys. This water portion of the survey must be terminated at two feet of water depth due to echosounder limits.
The end result is an integrated digital beach and bluff and an offshore profile. During this current episode of high Great Lakes water levels and rapid coastal change, we have found that this rapid, accurate, and cost-effective method of tracking coastal change is extremely beneficial for generating important datasets for coastal research and management.