LiDAR - Minnesota's Digital Elevation Project

LiDAR

LiDAR stands for “Light Detection And Ranging,” a technology that originated in the 1960’s as a combination of “light” and “radar”. LiDAR systems send a laser light pulse to target surfaces.  The light is reflected back to the system sensors where it is analyzed to capture the return time of travel from the surface.  The recorded time it takes for the light to return provides a measure of range (distance) to the target surface. 

Think of this technology as a virtual tape measure with the beam of light as the tape. This is the same science used by hand-held laser range finders commonly utilized in golfing and hunting to measure distance.  In a LiDAR system, the light pulses are combined with high accuracy global positioning systems (GPS) to determine the location of the source equipment and the resulting target surfaces.  From this information, a point is created representing those surfaces in a computer-generated model.  LiDAR sensors collect millions of these points where collectively they form a “point cloud” of data representing a 3D rendering of all the surfaces encountered by the laser pulses.

The new elevation data for Minnesota was acquired using LiDAR instrumentation mounted on fixed wing aircraft to map the earth’s surface, capturing all of the natural and human made features upon it. The information contained in the Minnesota point cloud data allows technicians and scientists to generate various landscapes such as ground, buildings and trees used for map making, resource inventory and modeling purposes.

Background

Minnesota, the land of 10,000 lakes, is fortunate to have an abundance of clean, clear water. Our communities have evolved from the benefits and transit capabilities of our waters; many of us still define our lives around the waters in this state. Placing a high value on these water resources, the citizens of Minnesota voted to establish the Clean Water, Land, and Legacy Amendment in 2008. As a result, a portion of the state’s sales tax is dedicated to the Clean Water Fund, which supports projects and products that protect, preserve and improve the water quality of Minnesota.

The Need for Topographic Information

Most, if not all, of these projects require detailed and accurate information that describes the lay of the land. The morphology of the landscape defines how precipitation transforms into flowing water, and subsequently that flowing water shapes the landscape. Detailed topographic information is essential to understanding this dynamic process and the human influences on the hydrologic systems of earth.

To meet this need, a portion of the Clean Water Fund was used to compile a highly detailed and accurate elevation data set for the entire state in a consistent format and to make it readily available without charge to the public. 

Modern Data

The U.S. Geological Survey (USGS) 1:24,000-scale quadrangle maps provided the initial coverage of statewide topographic contours.  The elevation information was derived from stereo aerial photography generally in the 1960’s and 1970’s.  The contours on these 1,745 individual maps also provided 30-meter digital elevation model (DEM) data for the entire state.  For many years resource managers and citizens have relied on these base topographic maps for terrain representation, which over time have become increasingly out-of-date.  Thanks to advances in technology and the formation of data collection and evaluation partnerships, a new elevation collection project was possible using LiDAR.

Cooperation and Collaboration

This LiDAR elevation mapping project was a partnership between state, federal, county and city governments and academic institutions in Minnesota. These partnerships, occurring at all levels of the project, were the foundation for a coordinated statewide LiDAR data collection. 

In some areas of the state, existing data was acquired and transformed to state standards. The remaining areas, which had older data or none at all, were collected by vendors under contract and added to the existing coverage. This amalgamation of data has resulted in a statewide seamless, modern representation of detailed topography for viewing and downloading.

Cooperative Funding

This valuable data is available to the public thanks to cooperative funding initiatives. With oversight from the Minnesota Elevation Committee, Minnesota’s modern elevation mapping project was completed with funding from the Clean Water Fund of the Land and Legacy Amendment.  Collections in the northwest and west-central areas were funded through the Red River Basin Mapping Initiative which pooled resources from many funding partners.  Collections in the southeast were funded through state flood relief and mitigation monies in response to the 2007 flood. Several counties and cities funded data collections within their boundaries or provided funding to increase the LiDAR point density for their jurisdiction.

Cooperative Quality Control

Quality control was critical to the success of Minnesota’s elevation mapping project.  Again, a cooperative approach was taken to bring efficiencies and lower cost into the project under the guidance of MnDOT survey staff.  Many counties across the state provided assistance and staff time to gather detailed ground-survey information that was used to verify the accuracy of the data collected by the LiDAR vendors. In other areas, Department of Transportation surveyors gathered this information. This information was then used by Minnesota Department of Natural Resources staff to assess the accuracy of the information and ensure that it was within contractual guidelines.