Southeast Minnesota LiDAR Project Completed! By Tim Loesch, Minnesota Department of Natural Resources
In August 2007, a rainfall event dumped more than 10 inches of rain over a large swath of southeastern Minnesota. The flooding that ensued was responsible for damage estimated at $67 million, affecting 4,200 homes and tragically resulting in seven deaths. Seven counties were declared disaster areas: Dodge, Fillmore, Houston, Olmsted, Steele, Wabasha and Winona – a total of approximately 4,100 square miles.
The Minnesota Legislature responded by appropriating monies to aid in the flood relief and to provide mitigation against future flood events. Acquisition of high-resolution elevation data using LiDAR technology was targeted as one of the outcomes of that mitigation and data collection was approved in April 2008. The project was coordinated by the Mn DNR and several partners including the U.S. Geological Survey, Mn/DOT and staff from affected counties. The project area grew to include Mower and Freeborn counties with $75,000 from the USGS and $122,000 from the two counties, and Turtle Creek, Shell Rock River and Cedar River Watershed Districts. This expanded the study area to 5,500 square miles.
A view of the Lake Zumbro Dam on the Zumbro River near Rochester.
A contract was awarded to Aerometric, Inc. and data collection was conducted in November 2008. Data started flowing in to the DNR for QA/QC starting in April 2009. Products delivered included one-meter resolution DEMs, two-foot contours, edge-of-water breaklines and LAS points. Required vertical accuracy was 18 centimeters (a bit more than 7 inches) as measured using methodologies outlined by the National Standard for Spatial Data Accuracy (NSSDA).
These data were independently validated using control points collected by county and contracted surveyors. In each county 100+ validation points were collected and used to verify the vertical accuracy of the LiDAR information. Accuracy assessments were completed by county and the following table shows the results (most are less than 6 inches).
Data was delivered in tiles that covered an area 1/16th of a 1:24,000-scale USGS quadrangle (approximately 3.25 square miles). As part of the processing, a one- and a three-meter county mosaic DEM was created and used for visual quality assessment.
County mosaics are being distributed on the DNR’s ftp site and are available by county. These data are being distributed as ESRI V9.3 file geodatabases and contains the breaklines, validation points, one- and three-meter DEMs and a shaded relief raster.
Individual tiles of contours, points and DEMs will be available soon on the DNR Data Deli.
These datasets were delivered to each of the partner counties on an external hard-drive. A GIS contact was identified in each county and they acted as the focal point for distribution to other entities in the county. An ArcGIS toolbox was created to assist local GIS staff in data projection, conversion and surface creation. This toolbox continues to grow and evolve as new applications and needs arise (available at ftp://ftp.dnr.state.mn.us/pub/gisftp/semn_lidar/semn_lidar_tools.zip).