2018 NYS ITS Lidar DEM: Cayuga and Oswego Counties, NY

Product: Raster digital elevation model (DEM) data.

Geographic Extent: Cayuga and Oswego County, New York, covering approximately 1,720 square miles.

Dataset Description: Cayuga and Oswego County, New York 2018 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 1.3. The data was developed based on a horizontal projection/datum of NAD83(2011), Universal Transverse Mercator Zone 18 N, meters and vertical datum of NAVD88 (GEOID12B), meters. Lidar data was delivered as processed Classified LAS 1.4 files, formatted to 1,980 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 the spring 2018, 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 48 ground control points that were used to calibrate the lidar to known ground locations established throughout the Cayuga and Oswego County, New York project area. An additional 125 independent accuracy checkpoints, 69 in Bare Earth and Urban landcovers (69 NVA points). 56 in Tall Grass and Brushland/Low Trees categories (56 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 GeoTIFF files hosted by USGS on Amazon Web Services.

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 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.

Raster File Type = IMG Bit Depth/Pixel Type = 32-bit float Raster Cell Size = 1 Meter Interpolation or Resampling Technique = Triangulated Irregular Network Required Vertical Accuracy = 19.6 cm NVA

Any conclusions drawn from the analysis of this information are not the responsibility of Axis Geospatial, LLC, New York Office of Information Technology Services, USGS, NOAA, the Office for Coastal Management or its partners.

Data is available online for bulk and custom downloads.

None

None. However, users should be aware that temporal changes may have occurred since this dataset was collected and that some parts of these data may no longer represent actual surface conditions. Users should not use these data for critical applications without a full awareness of the limitations of the data. Acknowledgement of New York Office of Information Technology Services would be appreciated for products derived from these data. The data represented is the result of data collection and processing per contract specifications and indicates the general existing conditions at the time of the 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.

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 69 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 56 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.

Non-Vegetated Vertical Accuracy (NVA) Check Points and Vegetated Vertical Accuracy (VVA) Check Points were independently surveyed and compared to the DEM data. For the NVA checkpoints, the overall RMSEz is 3.1 centimeters. This compares favorably to the USGS specification of < 10 cm. (USGS “LiDAR Base Specification vers. 1.3”, Page 4, Table 4;). The NVA at the 95% confidence level is 6.1 centimeters which is within the USGS specification of < 19.6 cm. (USGS “LiDAR Base Specification vers. 1.3”, Page 24, Table 4;)

Vegetated Vertical Accuracy (VVA) Check Point RMSEz is 6.6 centimeters and the VVA at the 95th percentile is 11.9 centimeters. The VVA of the DEM was calculated using 56 checkpoints located in the Brushlands and Low Trees and Tall Weeds and Crops land cover categories. The USGS specification for VVA at the 95th percentile is < 29.4 cm. (USGS “LiDAR Base Specification vers.1.3”, Page 24, Table 4;)

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. You may see data voids where caused by areas of low near infrared reflectivity, such as asphalt or composition roofing. We have seen these dropouts on building rooftops throughout this project. Also, there are extreme positive and negative Z values within the LiDAR pointcloud. We have classified these points as Class 7 (Low Point) and/or Class 18 (High Point) to accommodate for these values. Partially elevated water bodies may be present where use of Class 20 (Ignored Ground) next to the hydro breaklines has eliminated ground points on a small berm or raised bank.

Data covers the entire area specified for this project except there is a known data gap on the southeast corner of tile 4335081050. Partially elevated water bodies may be present where use of Class 20 (Ignored Ground) next to the hydro breaklines has eliminated ground points on a small berm or raised bank.

Data is backed up to tape and to cloud storage.

The NOAA Office for Coastal Management (OCM) ingested references to the USGS GeoTIFF files that are hosted on Amazon Web Services (AWS), into the Digital Coast Data Access Viewer (DAV). The DAV accesses the raster data as it resides on AWS.