Virtual viewer doesn’t see trees
Researchers at Michigan Technological University were hired by the Friends of the Huron Mountains (FOHM) to conduct a viewshed analysis of the wind farm proposed by Renewable Energy Systems (RES).
In explaining the process, the researchers said they started the analysis in December 2018 and finished in January.
According to Ryan Williams, assistant director of the Geospatial Research Facility at MTU, information on the height and position of each turbine was determined using permit applications filed with the Federal Aviation Administration (FAA) by RES. These permits are publicly available on the FAA website, oeaaa.faa.gov.
The analysis used a height on 279 feet for the turbines. This is the height of the center, or nacelle, of the spinning turbine blades.
While the blades could extend as much as 200 feet beyond the nacelle, the hub was used because the position of the blades would frequently change, according to FOHM president Burt Mason. Mason said navigation lights would be placed on the hub, not the blades.
The elevations on the map come from a US Geological Survey (USGS) National Elevation Dataset (NED) last updated in 2013. Ninety-five percent of the measurements are accurate to within 3.02 meters, according to USGS accuracy analysis completed in 2014.
The NED was created using several methods, including LiDAR, to create a complete topographical dataset. Its accuracy was checked against elevations from the National Geodetic Survey, which is created using GPS measurements at particular points.
This information was used to create the virtual viewer, which lets a user see what turbines in the RES-proposed locations would look like from any location. However, it does not take ground cover into account.
The analysis for FOHM is more thorough than a typical example, in that it also includes an estimation of obstruction by forested areas.
“As you can see on the map, it makes a very big difference,” Williams said in an email.
The first layer on the map is calculated with only ground elevation taken into account, and assuming a viewer height of about six feet.
For the second layer, a 52.5-foot obstruction was added in areas identified as forested in the 2017 USDA National Cropland Data. The USDA information breaks land down into 30-meter squares, and classifies them based on the majority land cover type within that square. The 52.5-foot height of the forest is an estimation.
Mason said he hopes people can use the two-dimensional map with the virtual viewer to get a good idea of how visible the proposed turbines will be from locations that matter to them like their home, fishing areas or hunting camp.
Including the obstructions caused by forested areas should increase the accuracy of the analysis, according to Williams. However, he said a lack of detailed data for objects smaller than 30 meters in size prevents the inclusion of features such as buildings, narrow fence rows, or trees in yards.
The results of the analysis are available at FOHM’s website, savethehuronmountains.org.