2017 USGS Lidar: West Central Illinois

Product: These lidar data are processed Classified LAS 1.4 files, formatted to 22,028 individual 2000 foot x 2000 foot tiles; used to create intensity images, 3D breaklines and hydro-flattened DEMs as necessary.

Geographic Extent: West Central Illinois, covering approximately 3,077 square miles. Counties included are Schuyler, Brown, Menard, Mason, Sangamon, and Morgan. A lidar survey was collected over two (2) areas of interest (AOI) in Illinois identified as the Base AOI and the Option AOI. The Base AOI covers approximately 1,926 square miles in total and the Option AOI covers approximately 1,151 square miles for a total of 3,077 square miles.

Dataset Description of the Original Data: West Central Illinois 2017 Lidar project called for the Planning, Acquisition, processing and derivative products of lidar data to be collected at a nominal pulse spacing (NPS) of 0.5 meter. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base Lidar Specification, Version 1.2; Quality Level 2+. The data was developed based on a horizontal projection/datum of NAD83 (2011), State Plane Coordinate System Illinois West (FIPS 1202), US Survey Feet and vertical datum of NAVD88 (GEOID12B), US Survey Feet. Lidar data was delivered as processed Classified LAS 1.4 files, formatted to 22,208 individual 2000 foot x 2000 US survey feet tiles, as 22,208 tiled Intensity Imagery, and as 22,209 tiled bare earth DEMs; all tiled to the same 2000 foot x 2000 foot schema. In an effort to preserve smooth continuity of the surface in which there are multiple overlapping swaths, an isolated area of cross flight line 229 was bit set at withheld in the following nine tiles: 2207_1295, 2207_1293, 2209_1297, 2209_1295, 2209_1293, 2311_1297, 2311_1295, 2311_1293, and 2313_1297. One tile located in Mason County, titled 2353_1367, did not contain LAS points as it consisted strictly of water with no ground points present. Therefore, no intensity image TIF could be produced for this tile, only a hydro-flattened DEM image is available. This tile is included in the tile index consisting of 22,209 tiles.

Ground Conditions: Lidar was collected in December 2017, while no snow was on the ground and rivers were at or below normal levels. In order to post process the lidar data to meet task order specifications and meet ASPRS vertical accuracy guidelines, Surveying and Mapping, LLC (SAM) established a total of 63 ground control points that were used to calibrate the lidar to known ground locations established throughout the Base AOI and Option AOI project areas. An additional 162 independent accuracy checkpoints, 91 in Bare Earth and Urban landcovers (91 NVA points), 71 in tall Grass/tall weeds/crops, Brush lands/short trees, Forested categories (71 VVA points), were used to assess the vertical accuracy of the data. These checkpoints were not used to calibrate or post process the data.

This metadata record supports the data entry in the NOAA Digital Coast Data Access Viewer (DAV). For this data set, the DAV is leveraging the Entwine Point Tiles (EPT) hosted by USGS on Amazon Web Services.

To acquire QL2+ lidar detailing surface elevation data, vegetation, and buildings for use to support the 3DEP mission, the Natural Resources Conservation Services (NRCS) Agricultural Drainage Water Management Initiative, National Water Quality Initiative and the Mississippi River Basin Initiative. Classified LAS files are used to show the manually reviewed bare earth surface. This allows the user to create Intensity Images, Breaklines and Raster DEM. The purpose of these lidar data was to produce high accuracy 3D hydro-flattened Digital Elevation Model (DEM) with a 2 US survey feet cell size. These lidar point cloud data were used to create intensity images, 3D breaklines, and hydro-flattened DEMs as necessary.

Any conclusions drawn from the analysis of this information are not the responsibility of NOAA, the Office for Coastal Management or its partners.

Data is available online for bulk and custom downloads.

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Users should be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations.

Microsoft Windows 7 Professional Service Pack 1; ESRI ArcCatalog 10.7.1

Twelve checkpoints were determined to be photo-identifiable in the intensity imagery and were used to test the horizontal accuracy of the LiDAR dataset. As only twelve (12) checkpoints were photo identifiable, the results are not statistically significant enough to report as a final tested value, but the results of are still provided. Using NSSDA methodology (endorsed by the ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014)), horizontal accuracy at the 95% confidence level (called ACCURACYr) is computed by the formula RMSEr * 1.7308 or RMSExy * 2.448. No horizontal accuracy requirements or thresholds were provided for this project. However, LiDAR datasets are generally calibrated by methods designed to ensure a horizontal accuracy of 1 meter or less.

Actual positional accuracy of this dataset was found to be RMSEx = 0.242 ft (7.389 cm) and RMSEy = 0.252 (7.696 cm) which equates to +/- 0.606 ft (18.466 cm) at 95% confidence level.

The specifications require that only non-vegetated vertical accuracy (NVA) be computed for raw lidar data swath files. The vertical accuracy was tested with 91 independent survey located in open terrain. These check points (check points) were not used in the calibration or post processing of the lidar data. The survey check points were distributed throughout the project. Specifications for this project require that the NVA be 19.6 centimeters (cm) or better AccuracyZ at 95-percent confidence level.

The NVA was tested using 91 independent survey located in open terrain. The survey check points were distributed throughout the project area. The checkpoints were distributed throughout the project area and were surveyed using GPS techniques. See survey report for additional survey methodologies. The link is provided in the URL section of this metadata record.

Elevations from the unclassified lidar surface were measured for the x,y location of each check point. Elevations interpolated from the lidar surface were then compared to the elevation values of the surveyed control. The root mean square error vertical (RMSEz) was computed to be 0.06253 meters. AccuracyZ has been tested to meet 19.6 cm NVA at 95-percent confidence level using (RMSEz * 1.9600) as defined by the National Standards for Spatial Data Accuracy (NSSDA); assessed and reported using American Society of Photogrammetry and Remote Sensing (ASPRS) Guidelines.

For more information see the lidar report. The link to this report is provided in the URL section of this metadata record.

These LAS data files include all data points collected. No points have been removed or excluded. A visual qualitative assessment was performed to ensure data completeness. No void areas or missing data exist. The raw point cloud is of good quality and data passes Non-Vegetated Vertical Accuracy specifications.

Data is backed up to cloud storage.

The NOAA Office for Coastal Management (OCM) ingested references to the USGS Entwine Point Tiles (EPT) hosted on Amazon Web Services (AWS) into the Digital Coast Data Access Viewer (DAV). The DAV accesses the point cloud as it resides on AWS under the usgs-lidar-public-container.