2016 NYSGPO Lidar DEM: Allegany and Steuben Counties, NY

Product: These are Digital Elevation Model (DEM) data for Allegany and Steuben County, New York as part of the required deliverables for the 2016 Allegany and Steuben County Lidar project. Class 2 (ground) lidar points in conjunction with the hydro breaklines were used to create a 1 meter hydro-flattened Raster DEM.

Geographic Extent: Allegany and Steuben County, New York, covering approximately 1,316 square miles.

Dataset Description: Allegany and Steuben County, New York 2016 Lidar project called for the Planning, Acquisition, processing and derivative products of lidar data to be collected at a nominal pulse spacing (NPS) of 0.7 meter. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base Lidar Specification, Version 1.2. Lidar data was delivered as flightline-extent unclassified LAS swaths, as processed Classified LAS 1.4 files, formatted to 1516 individual 1500 m x 1500 m tiles, as tiled bare earth DEMs; all tiled to the same 1500 m x 1500 m schema.

Ground Conditions: Lidar was collected in early 2016, 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, New York Office of Information Technology Services established a total of 26 ground control points that were used to calibrate the lidar to known ground locations established throughout the Allegany and Steuben County, New York project area. An additional 111 independent accuracy checkpoints, 61 in Bare Earth and Urban landcovers (61 NVA points). Please note that 3 of the 61 total NVA point were excluded from the solution due to being outside of the LiDAR coverage area. 50 in Tall Grass and Brushland/Low Trees categories (50 VVA points) were used to assess the vertical accuracy of the data. Please note that 2 VVA points out of the 50 collected were excluded due to being outside of the collection area. These checkpoints were not used to calibrate or post process the data.

In addition to these bare earth Digital Elevation Model (DEM) data, the lidar point data that these DEM data were created from, are also available. These data are available for custom download at the link provided in the URL section of this metadata record.

To acquire detailed surface elevation data for use in conservation planning, design, research, floodplain mapping, dam safety assessments and elevation modeling, etc. 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 1 meter cell size. These raw lidar point cloud data were used to create classified lidar LAS files, 3D breaklines, hydro-flattened DEMs as necessary.

USGS Contract No. G16AC00068 CONTRACTOR: New York Office of Information Technology Services. SUBCONTRACTOR: Axis Geospatial, LLC Lidar data were acquired and calibrated by Axis GeoSpatial, LLC. All follow-up processing was completed by the prime contractor. This material is based upon work supported by the Natural Resources Conservation Service, U.S. Department of Agriculture, under number 68-2C31-15-501.Raster File Type = IMGBit Depth/Pixel Type = 32-bit floatRaster Cell Size = 1 MeterInterpolation or Resampling Technique = Triangulated Irregular NetworkRequired Vertical Accuracy = 19.6 cm NVA

Overall Project Metadata

The data represented is the result of data collection and processing per contract specifications and indicates the general existing conditions at the time of data collection. As such, it is only valid for its intended use, content, time, and accuracy specifications. The user is responsible for the results of any application of the data for other than its intended purpose.

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.

None

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.

Horizontal error in lidar derived elevation data is largely a function of positional error as derived from the Global Navigation Satellite System (GNSS), attitude (angular orientation) error (as derived from the INS) and flying altitude; and can be estimated based on these parameters. As described in Section 7.5 of the ASPRS Positional Accuracy Standards for Digital GeoSpatial Data the horizontal errors in lidar data are largely a function of GNSS positional error, INS angular error, and flying altitude. Therefore lidar data collected with GNSS error of 0.05m and the IMU error of 0.005 degrees at an altitude of 1830 m; the expected radial horizontal positional error will be RMSEr = 0.29 m.

The project specifications require the accuracy (ACCz) of the derived DEM be calculated and reported in two ways:

1. The required NVA is: 19.6 cm at a 95% confidence level, derived according to NSSDA, i.e., based on RMSE of 10 cm in the “bare earth” and "urban" land cover classes. This is a required accuracy. The NVA was tested with 58 checkpoints located in bare earth and urban (non-vegetated) areas.

2. Vegetated Vertical Accuracy (VVA): VVA shall be reported for "brushlands/low trees" and "tall weeds/crops" land cover classes. The target VVA is: 29.4 cm at the 95th percentile, derived according to ASPRS Guidelines, Vertical Accuracy Reporting for Lidar Data, i.e., based on the 95th percentile error in all vegetated land cover classes combined. This is a target accuracy. The VVA was tested with 48 checkpoints located in tall weeds/crops and brushlands/low trees (vegetated) areas. The checkpoints were distributed throughout the project area and were surveyed using GPS techniques. See survey report for additional survey methodologies.

AccuracyZ has been tested to meet 19.6 cm or better Non-Vegetated Vertical Accuracy at 95% confidence level using RMSE(z) x 1.9600 as defined by the National Standards for Spatial Data Accuracy (NSSDA); assessed and reported using National Digital Elevation Program (NDEP)/ASRPS Guidelines.

Tested 0.153 meters NVA at a 95% confidence level using RMSE(z) x 1.9600 as defined by the National Standards for Spatial Data Accuracy (NSSDA). The NVA of the DEM was calculated using 58 independent checkpoints located in the Bare Earth and Urban land cover categories.

Tested 0.135 meters VVA at a 95% confidence level was calculated using 48 checkpoints located in the Brushlands and Low Trees and Tall Weeds and Crops land cover categories at the 95th percentile, derived according to ASPRS Guidelines, Vertical Accuracy Reporting for Lidar Data. Tested against the DEM.

Datasets contain complete coverage of tiles with the exception of three tiles on the outer edges of the project area, u_2505069200_2016.img, u_2520071300_2016.img and u_2535071300_2016.img. No points have been removed or excluded. A visual qualitative assessment was performed to ensure data completeness. There are no void areas or missing data. The raw point cloud is of good quality and data passes Non-Vegetated Vertical Accuracy specifications. Points with extreme elevations (negative values, or positive values well above the expected maximum) are present in this dataset. These points are classified as low or high noise in classified point cloud tiles.

Data covers the entire area specified for this project. Partially elevated water bodies may be present where use of Class 10 (Ignored Ground) next to the hydro breaklines has eliminated ground points on a small berm or raised bank. On some smaller bridges breaklines were created to prevent triangulation across the gap in the bare earth DEM.

Data is backed up to tape and to cloud storage.

Data were collected and processed by Axis GeoSpatial, LLC for the New York Office of Information Technology Services and posted to their ftp site. The NOAA Office for Coastal Management (OCM) downloaded the data from the ftp site and processed it to make it available for custom download from the Data Access Viewer (DAV) and bulk download from https.