Thursday, January 15, 2015
High resolution elevation data now available through DNR
Agricultural professionals and producers, with or without GIS software, now have access at no cost to the Minnesota high resolution elevation data collected with LiDAR laser scanning. The Minnesota DNR released MnTOPO in 2014, a web application for viewing, printing and downloading the data. http://www.dnr.state.mn.us/maps/mntopo/index.html
From a computer or mobile device you can view contour lines at two, ten, or fifty foot elevation intervals projected over one of four basemaps. They include roads, aerial images, colored terrain, and black and white terrain images. The user can also obtain an elevation profile for a line drawn on the map. MnTOPO navigation is similar to that of Google Earth, allowing zooming and panning to locate a desired area or point, and has a location search capability. The contour lines appear at increasingly higher resolution (decreasing intervals) when zooming in on an area, and each contour resolution can be turned on or off by the user. Maps can be created, saved and printed.
The data can also be downloaded for GIS software directly from MnTOPO. The user draws a polygon around an area on the map and then selects the LiDAR products desired for that area from a list that includes contours, digital elevation models (DEM), hillshade images, and classified point data. The data are then automatically assembled and a link for ftp download is emailed to the user.
The LiDAR data were obtained from light aircraft scanning the earth surface with laser pulses, one pulse for every 1.5 square meters. Several “returns” (reflections) are obtained for each pulse, corresponding to the altitude of the reflecting surface, like vegetation and bare earth. The data were collected in late fall and early spring, avoiding as much green leaf tissue or snow as possible in order to maximize the bare earth surface measured. One hundred ground surveyed points per county were used to verify the target vertical accuracy of about seven inches on average. Deviations are most commonly found in areas of very dense vegetation like cattail wetlands. The overall accuracy is an order of magnitude greater than previously available elevation data, except for that from surveyed points and RTK technology.
The data are being used in rural areas for many applications, including delineation of field management zones, erosion prediction, siting and pre-design of conservation structures and drainage systems, wetland restoration, flood management, and many others. These can take place any time of year, including when the crop is in the field or snow is covering the ground, since the data are already available for the entire state.