2018 USGS Lidar: Post Hurricane Maria - USVI

Product: These lidar data are processed Classified LAS 1.4 files, formatted to 301 individual 1500 m x 1500 m tiles; used to create intensity images, 3D breaklines and hydro-flattened DEMs as necessary.

Geographic Extent: St. Croix, US Virgin Islands, covering approximately 82 square miles & St. Thomas and St. John, US Virgin Islands, covering approximately 52 square miles.

Dataset Description: PR USVI Lidar project called for the Planning, Acquisition, processing and derivative products of lidar data to be collected at a nominal pulse spacing (NPS) of 0.35 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), Puerto Rico and Virgin Islands, meters and vertical datum of VIVD09 (GEOID12B), meters. Lidar data was delivered as processed Classified LAS 1.4 files, formatted to 143 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 in late 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, Leading Edge Geomatics established a total of 4 ground control points that were used to calibrate the lidar to known ground locations established throughout the St. Croix, US Virgin Islands project area. An additional 28 independent accuracy checkpoints, 22 in Bare Earth and Urban landcovers (22 NVA points), 6 in Tall Grass and Brushland/Low Trees categories (6 VVA points), were used to assess the vertical accuracy of the data. These checkpoints were not used to calibrate or post process the data.

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 0.5 meter cell size. These raw lidar point cloud data were used to create classified lidar LAS files, intensity images, 3D breaklines, hydro-flattened DEMs as necessary.

USGS Contract No. G16PC00020 CONTRACTOR: Dewberry SUBCONTRACTOR: Leading Edge Geomatics Lidar data were acquired and calibrated by Leading Edge Geomatics. 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 v1.3",

"ldrsens" : "Riegl VQ1560i",

"ldrmaxnr" : "Infinite",

"ldrnps" : "0.31",

"ldrdens" : "10.3",

"ldranps" : "0.31",

"ldradens" : "10.3",

"ldrfltht" : "1000",

"ldrfltsp" : "150",

"ldrscana" : "57",

"ldrscanr" : "175x2",

"ldrpulsr" : "700x2",

"ldrpulsd" : "3",

"ldrpulsw" : "0.8994",

"ldrwavel" : "1064",

"ldrmpia" : "1",

"ldrbmdiv" : "0.25",

"ldrswatw" : "1086",

"ldrswato" : "20",

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

},

"ldrinfo" : {

"ldrspec" : "U.S. Geological Survey (USGS) - National Geospatial Program (NGP) Lidar Base Specification v1.3",

"ldrsens" : "Riegl Q780",

"ldrmaxnr" : "Infinite",

"ldrnps" : "0.42",

"ldrdens" : "5.7",

"ldranps" : "0.30",

"ldradens" : "11.4",

"ldrfltht" : "800",

"ldrfltsp" : "100",

"ldrscana" : "60",

"ldrscanr" : "122",

"ldrpulsr" : "400",

"ldrpulsd" : "3",

"ldrpulsw" : "0.8994",

"ldrwavel" : "1064",

"ldrmpia" : "1",

"ldrbmdiv" : "0.25",

"ldrswatw" : "924",

"ldrswato" : "50",

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

},

"ldraccur" : {

"ldrchacc" : "0.341",

"rawnva" : "0.148",

"rawnvan" : "91",

"clsnva" : "0.132",

"clsnvan" : "96",

"clsvva" : "0.270",

"clsvvan" : "71"

},

"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" : "17",

"clasitem" : "Bridge Decks"

},

"lasclass" : {

"clascode" : "18",

"clasitem" : "High Noise"

},

"lasclass" : {

"clascode" : "20",

"clasitem" : "Ignored Ground"

}

}}

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.

The island of Puerto Rico and its surrounding islands were produced to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 41 cm RMSEx/RMSEy Horizontal

Accuracy Class which equates to Positional Horizontal Accuracy = +/- 1 meter at a 95% confidence level. Seventeen (17) checkpoints were photo-identifiable but do not produce a

statistically significant tested horizontal accuracy value. Using this small sample set of photo identifiable checkpoints, positional accuracy of this dataset was found to be RMSEx = 15.5 cm

and RMSEy = 12.2 cm which equates to +/- 34.1 cm at 95% confidence level. While not statistically significant, the results of the small sample set of checkpoints are within the produced to meet horizontal accuracy

For St. Croix, the tested RMSEz of the classified lidar data for checkpoints in non-vegetated terrain equaled 6.6 cm compared with the 10 cm specification; and the NVA of the classified lidar data computed using RMSEz x 1.9600 was equal to 12.9 cm, compared with the 19.6 cm specification.

For St. Croix, the tested VVA of the classified lidar data computed using the 95th percentile was equal to 9.5 cm, compared with the 29.4 cm specification.

For St. John and St. Thomas, the tested RMSEz of the classified lidar data for checkpoints in non-vegetated terrain equaled 5.2 cm compared with the 10 cm specification; and the NVA of the classified lidar data computed using RMSEz x 1.9600 was equal to 10.2 cm, compared with the 19.6 cm specification.

For St. John and St. Thomas, the tested VVA of the classified lidar data computed using the 95th percentile was equal to 11.1 cm, compared with the 29.4 cm specification. Additional accuracy information and statistics for the classified lidar data, raw swath data, and bare earth DEM data are found in the following sections of this report.

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. The NVA of Puerto Rico, the U.S. Virgin Islands, and the surrounding islands will be tested with 91 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 will be 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.

Datasets contain complete coverage of tiles. 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.

Data covers the entire area specified for this project.

Data is backed up to tape and to cloud storage.