By Tim Loesch, Minnesota Department of Natural Resources
The DNR and a number of partners have been working together to fund the collection of high-quality elevation data using LIDAR technology for 3600 square miles within the Red River watershed. This spring, data for 60% of the project area was collected with the remainder scheduled to be collected this fall. Project partners include the Federal Emergency Management Agency, the Minnesota Department of Transportation, local units of government (including Norman and Clay counties), the Wild Rice Watershed District, the White Earth Reservation and a variety of other agencies and organizations in the Red River Valley.
In August we got our first look at the data with the delivery of a pilot project area to the DNR GIS section for quality control and validation of the contracted deliverable products. The pilot project covers approximately 180 square miles and the total data volume for this area was 92 gigabytes. The delivered products included raw LIDAR as well as processed data for bare earth, vegetation, buildings, first and last returns and an interesting product that records the intensity of the LIDAR return and looks much like an air photograph. The image below is a small area within the town of Ada in Norman County. You can plainly see roadways, houses, a golf course, vegetation and bare earth.
After spending a couple of days processing and reviewing the data it was concluded that the data was very good although it needed a bit of tweaking to remove effects from vegetation on the bare earth data.
Using 23 validation points provided by Mn/DOT survey crews, the elevation data proved to be very good indeed. In urban and agricultural field environments the data was particularly good with six of the sites having elevation values within 1/10 of a foot, eight sites within ½ foot and eight sites within a foot. Only one site had a LIDAR error of more than a foot at 1.277. It was noted that this site was in a swamp that had water in it during the spring during the LIDAR collection and was dry when the survey was done in late July. This may account for the higher level of error at this site. A histogram of the sites is shown below, the Y-axis represents the number of points while the X-axis shows the level of error. Eight of the points had errors of less than .01.
One of the products is a one-meter raster representing the bare earth elevation surface.
The image below shows a shaded relief perspective of a larger area within the town of Ada that has the Wild Rice River flowing through the center of the image. This map clearly shows a series of flood control structures used to protect the city from flooding.
From this surface a set of one-foot contours was generated. The image below shows a small sample area of a river drainage surrounded by agricultural lands.
Delivery of the final data of the spring flight area is expected in early September. Current plans are to make the raster and vector data available on the DNR GIS Data Deli for download.