2017 NRCS/FEMA/USGS Lidar: South Central VA

Product: These lidar data are processed Classified LAS 1.4 files, formatted to 11495 individual 1500 m x 1500 m tiles; used to create intensity images, 3D breaklines and hydro-flattened DEMs as necessary.

Geographic Extent: Virginia and West Virginia, covering approximately 9431 square miles.

Dataset Description: VA FEMA NRCS South Central 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 0.7 meter. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base Lidar Specification, Version 1.2. The data was developed based on a horizontal projection/datum of NAD83 (2011), Universal Transverse Mercator, meters and vertical datum of NAVD88 (GEOID12B), meters. Lidar data was delivered as processed Classified LAS 1.4 files, formatted to 11495 individual 1500 m x 1500 m tiles, as tiled Intensity Imagery, and as tiled bare earth DEMs; all tiled to the same 1500 m x 1500 m schema.

Ground Conditions: Lidar was collected from mid 2017 to mid 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, Dewberry established a total of 63 ground control points that were used to calibrate the lidar to known ground locations established throughout the VA FEMA NRCS South Central project area. An additional 331 independent accuracy checkpoints, 190 in Bare Earth and Urban landcovers (190 NVA points),141 in Tall Grass and Brushland/Low Trees categories (141 VVA points), were used to assess the vertical accuracy of the data. These checkpoints were not used to calibrate or post process the data.

Data were subsequently reprocessed to Entwine Point Tile (EPT) format in web mercator projection with vertical meters. The EPT form of the data is used by the NOAA Digital Coast Data Access Viewer, which this metadata record is supporting. Additional processing steps may have been done by the Data Access Viewer and will be recorded in the lineage section.

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 lidar point cloud data were used to create intensity images, 3D breaklines, and hydro-flattened DEMs as necessary.

USGS Contract No. G16PC00020 CONTRACTOR: Dewberry SUBCONTRACTOR: Leading Edge Geomatics (LEG) and Axis Geospatial, LLC Lidar data were acquired and calibrated by Aerial Scanning Services. All follow-on processing was completed by the prime contractor.

The following are the USGS lidar fields in JSON:

{

"ldrinfo" : {

"ldrspec" : "U.S. Geological Survey (USGS) - National Geospatial Program (NGP) Lidar Base Specification v1.2",

"ldrsens" : "Riegl VQ-780i",

"ldrmaxnr" : "15",

"ldrnps" : "1.0",

"ldrdens" : "1.0",

"ldranps" : "0.7",

"ldradens" : "2.0",

"ldrfltht" : "1600",

"ldrfltsp" : "100",

"ldrscana" : "60",

"ldrscanr" : "74",

"ldrpulsr" : "300",

"ldrpulsd" : "3",

"ldrpulsw" : "0.9",

"ldrwavel" : "1064",

"ldrmpia" : "1",

"ldrbmdiv" : "0.25",

"ldrswatw" : "1848",

"ldrswato" : "55",

"ldrgeoid" : "National Geodetic Survey (NGS) Geoid12B"

},

"ldrinfo" : {

"ldrspec" : "U.S. Geological Survey (USGS) - National Geospatial Program (NGP) Lidar Base Specification v1.2",

"ldrsens" : "Riegl LMS-Q1560",

"ldrmaxnr" : "15",

"ldrnps" : "0.7",

"ldrdens" : "2.0",

"ldranps" : "0.7",

"ldradens" : "2.0",

"ldrfltht" : "2087",

"ldrfltsp" : "150",

"ldrscana" : "58.52",

"ldrscanr" : "153",

"ldrpulsr" : "687",

"ldrpulsd" : "3",

"ldrpulsw" : "0.90",

"ldrwavel" : "1064",

"ldrmpia" : "1",

"ldrbmdiv" : "0.25",

"ldrswatw" : "2338",

"ldrswato" : "15",

"ldrgeoid" : "National Geodetic Survey (NGS) Geoid12B"

},

"ldrinfo" : {

"ldrspec" : "U.S. Geological Survey (USGS) - National Geospatial Program (NGP) Lidar Base Specification v1.2",

"ldrsens" : "Riegl VQ-1560i",

"ldrmaxnr" : "15",

"ldrnps" : "0.7",

"ldrdens" : "2.0",

"ldranps" : "0.7",

"ldradens" : "2.0",

"ldrfltht" : "2087",

"ldrfltsp" : "150",

"ldrscana" : "58.52",

"ldrscanr" : "153",

"ldrpulsr" : "687",

"ldrpulsd" : "3",

"ldrpulsw" : "0.90",

"ldrwavel" : "1064",

"ldrmpia" : "1",

"ldrbmdiv" : "0.25",

"ldrswatw" : "2338",

"ldrswato" : "15",

"ldrgeoid" : "National Geodetic Survey (NGS) Geoid12B"

},

"ldraccur" : {

"ldrchacc" : "0.672",

"rawnva" : "0.117",

"rawnvan" : "183",

"clsnva" : "0.113",

"clsnvan" : "190",

"clsvva" : "0.211",

"clsvvan" : "141"

},

"lasinfo" : {

"lasver" : "1.4",

"lasprf" : "6",

"laswheld" : "Withheld (ignore) points were identified in these files using the standard LAS Withheld bit.",

"lasolap" : "Swath "overage" points were identified in these files using the standard LAS overlap bit.",

"lasintr" : "16",

"lasclass" : {

"clascode" : "1",

"clasitem" : "Processed, but Unclassified"

},

"lasclass" : {

"clascode" : "2",

"clasitem" : "Bare Earth Ground"

},

"lasclass" : {

"clascode" : "7",

"clasitem" : "Low Noise"

},

"lasclass" : {

"clascode" : "9",

"clasitem" : "Water"

},

"lasclass" : {

"clascode" : "10",

"clasitem" : "Ignored Ground"

},

"lasclass" : {

"clascode" : "17",

"clasitem" : "Bridge Decks"

},

"lasclass" : {

"clascode" : "18",

"clasitem" : "High Noise"

}

}}

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 or 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.

Tested Non-Vegetated Vertical Accuracy = 0.117 meters 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 raw lidar point cloud swath files was calculated against TINs derived from the final calibrated and controlled swath data using 183 independent checkpoints located in Bare Earth and Urban land cover classes.

The project specifications require that only Non-Vegetated Vertical Accuracy (NVA) be computed for raw lidar point cloud swath files. The required accuracy (ACCz) 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. Eight checkpoints (NVA-10, 125, 127, 141, 143, 147, 153, and 157) were removed from the raw swath vertical accuracy testing due to proximity to vegetation. Only non-vegetated terrain checkpoints are used to test the raw swath data because the raw swath data has not been classified to remove vegetation, structures, and other above ground features from the ground classification. Three of these points (NVA-10, 125, and 127) were located in open terrain, but were obscured by overhead branches or transient objects (vehicles). Points NVA- 141, 143, 153, and 157 were removed due to sensor noise modeled by the lidar point cloud. These high points caused erroneous high values during the swath vertical accuracy testing; therefore, these points were removed from the final calculations. Once the data underwent the classification process, the vegetation, objects and high noise were removed from the final ground classification and these seven checkpoints were added back into the final vertical accuracy testing.

NVA-147 was positioned next to a steep mountain slope and close to mature trees. The erroneously high survey elevation is likely the result of multipathing errors, which result when vertical obstructions either partially block or "bounce" the GPS signal, producing incorrect position information. This point was removed from all testing.

The NVA was tested with 183 checkpoints located in bare earth and urban (non-vegetated) areas. These check points were not used in the calibration or post processing of the lidar point cloud data. The checkpoints were distributed throughout the project area and were surveyed using GPS techniques. See survey report for additional survey methodologies. 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 points. 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.

These LAS data files include all data points collected. No points have been removed or excluded, including synthetic points. Additional information regarding the synthetic points can be found in the final project report delivered to USGS. 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 covers the entire area specified for this project.

Data is backed up to cloud storage.