COMPARISON OF AIRBORNE LIDAR ELEVATION DATA AND USGS NATIONAL ELEVATION DATASET INFORMATION FOR INPUTS TO REGIONAL AND LARGE-SCALE GEOLOGIC MAPPING APPLICATIONS IN ILLINOIS

As a partner agency in the Illinois Height Modernization Program funded by the National Geodetic Survey, the Illinois State Geological Survey (ISGS) is the primary in-state point-of-contact for county-based airborne LiDAR elevation data, as well as the responsible agency for providing public access and distribution of all LiDAR data products. The receipt of this high-resolution, improved LiDAR technology elevation data has afforded ISGS scientists an unusual opportunity to investigate the potential of LiDAR in geographic areas of the state which have been prioritized for geological mapping applications. The airborne LiDAR last returns data received by the ISGS averages 1.0-1.2 meter horizontal resolution and 0.3-0.4 meter vertical resolution, and first returns data typically exhibit a higher horizontal resolution. This enhanced spatial resolution has resulted in the discovery by ISGS mapping geologists of fine-resolution landscape features within continental glaciated terrain, as well as within areas where bedrock is at or near the surface.

The introduction of LiDAR into the ISGS geologic mapping program has created scientific curiosity about the appropriateness and accuracy of the topographic information contained within the U.S. Geological Survey's National Elevation Dataset (NED), most especially the digital elevation models produced from 1 arc-second (30 meter) and 1/3 arc-second (10 meter) source data, both of which are much coarser in horizontal and vertical resolution than LiDAR. Currentness of the NED data is also a concern, particularly in active geomorphic areas of the state, because the source information for the Illinois portion of the NED is several decades old. Using a ten meter average cell size as the unit of measurement, analysis shows there is a difference of ten feet between LiDAR and NED elevation values for approximately 44 percent of a typical size county area; an additional 40 percent of the county area shows little difference. Elevation differences greater than ten feet are in isolated areas and can be largely attributed to land use change (e.g., mining and quarrying), forest cover, and near-surface geomorphic processes. Elevation differences at the 7.5-minute quadrangle scale are more variable and indicate the requirement of LiDAR data for large scale mapping applications.