2017 USGS 3DEP Lidar: Fairbanks, AK (QL1 & QL2)

In May 2017, Quantum Spatial (QSI) was contracted by the United States Geological Survey (USGS) to collect QL1 and QL2 Light Detection and Ranging (LiDAR) data over approximately 1.8 million acres of land for the Fairbanks 3DEP mapping site in Alaska (Task Order G17PD00606). Data were collected to aid USGS in assessing the topographic and geophysical properties of the study area to support the 3DEP mapping initiative.

Geographic Extent: The QL1 area encompasses 248,555 acres and the QL2 area encompasses 1,186,822 acres.

Dataset Description: RAW flight line swaths were processed to create 6,268 classified LAS 1.4 files delineated in 3000 x 3000 ft tiles tiles. Each LAS file contains LiDAR point information, which has been calibrated, controlled, and classified. LAS files have been edited to the extent of the buffered boundary. Additional derived products include intensity images, hydro-flattened DEMs, highest hit surface models, 2ft contours, and 3D breaklines of rivers and lakes within the study area.

Ground Conditions: Data was acquired during conditions with an absence of snow, high water, ground fog and/or clouds below the flight altitudes.

The NOAA Office for Coastal Management (OCM) downloaded 1203 laz files from ftp://rockyftp.cr.usgs.gov/vdelivery/Datasets/Staged/Elevation/LPC/Projects/USGS_LPC_AK_FairbanksNSB_QL1_2017_LAS_2018/ and 6268 laz files from ftp://rockyftp.cr.usgs.gov/vdelivery/Datasets/Staged/Elevation/LPC/Projects/USGS_LPC_AK_FairbanksNSB_QL2_2017_LAS_2018 and processed the data to the Data Access Viewer (DAV) and https.

Hydro and bridge breaklines are also available. These data are available for download at the link provided in the URL section of this metadata record. Please note that these products have not been reviewed by the NOAA Office for Coastal Management (OCM) and any conclusions drawn from the analysis of this information are not the responsibility of NOAA or OCM.

The purpose of the lidar data was to produce a high accuracy 3D dataset that meets all necessary standards laid out by the 3DEP initiative.

The raw lidar point cloud data were used to create classified lidar LAS files, intensity images, hydro-flattened DEMs, highest hit surface models, 2ft contours, and 3D breaklines of rivers and lakes within the study area.

CONTRACTOR: Quantum Spatial, Inc.

Ground Control Points were acquired DOWL Engineering. All Lidar data acquisition, calibration, and follow-on processing were completed by the prime contractor.

The following are the USGS lidar fields in JSON:

{

"ldrinfo" : {

"ldrspec" : "National Geospatial Program Lidar Base Specification Version 1.2",

"ldrsens" : "ALS-70",

"ldrmaxnr" : "15",

"ldrnps" : ".71",

"ldrdens" : "2",

"ldranps" : "0.71",

"ldradens" : "2",

"ldrfltht" : "1600",

"ldrfltsp" : "145",

"ldrscana" : "30",

"ldrscanr" : "50.2",

"ldrpulsr" : "175",

"ldrpulsd" : "9",

"ldrpulsw" : "2.698",

"ldrwavel" : "1064",

"ldrmpia" : "1",

"ldrbmdiv" : "22",

"ldrswatw" : "857",

"ldrswato" : "28",

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

},

"ldraccur" : {

"ldrchacc" : "0.5",

"rawnva" : "0.376 ft",

"rawnvan" : "321"

},

"lasinfo" : {

"lasver" : "1.4",

"lasprf" : "6",

"laswheld" : "Withheld points are identified using the standard LAS witheld bit.",

"lasolap" : "Swath overage points are identified using the standard LAS overlap bit.",

"lasintr" : "16",

"lasclass" : {

"clascode" : "1",

"clasitem" : "Processed, but Unclassified"

},

"lasclass" : {

"clascode" : "2",

"clasitem" : "Bare earth ground"

},

"lasclass" : {

"clascode" : "3",

"clasitem" : "Low Vegetation (0.5m - 2m)"

},

"lasclass" : {

"clascode" : "4",

"clasitem" : "Medium Vegetation (2m - 6m)"

},

"lasclass" : {

"clascode" : "5",

"clasitem" : "High Vegetation (6m+)"

},

"lasclass" : {

"clascode" : "6",

"clasitem" : "Buildings (automated classification only)"

},

"lasclass" : {

"clascode" : "7",

"clasitem" : "Low Noise"

},

"lasclass" : {

"clascode" : "9",

"clasitem" : "Water"

},

"lasclass" : {

"clascode" : "10",

"clasitem" : "Ignored Ground Near Breakline"

},

"lasclass" : {

"clascode" : "17",

"clasitem" : "Bridge Decks"

}

}}

Any conclusions drawn from the analysis of this information are not the responsibility of Quantum Spatial, Inc, USGS, 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.

LASTools, TerraPOS, Cloudpro 1.2.4, Microstation Version 8i, TerraScan Version 17, TerraModeler Version 17, ESRI ArcGIS 10.3, Windows 7 Operating System

The specifications require that raw Non-vegetated Vertical Accuracy (NVA) be computed from the both the raw lidar point cloud swath files and the derived DEMs. Additionally, Vegetated Vertical Accuracy (VVA) is also to be computed from the derived DEMS. The NVA check points were collected by DOWL Engineering and distributed throughout the project as feasible. These check points were not used in the calibration or post processing of the lidar point cloud data. The VVA was collected by DOWL Engineering and tested with independent check points located in vegetated terrain, also witheld from the calibration and post processing of the lidar point cloud data and distributed throughout the project area as feasible. Specifications for this project require that the NVA be 19.6 cm (Swath, DEM) meters or better AccuracyZ at 95% confidence level and that the VVA be 29.4 cm (DEM) or better AccuracyZ at the 95th percentile. The following accuracy assessment reflects the combined accuracy results of QL1 and QL2 data.

0.115 m (0.376 ft) AccuracyZ at the 95 percent Confidence Interval for RAW LAS NVA.

DEM NVA: 0.094 m (0.309 ft) AccuracyZ at the 95 percent Confidence Interval.

DEM VVA: 0.209 m (0.687 ft) AccuracyZ at the 95th percentile.

NVA was tested using 321 surveyed check points. Elevations interpolated from the unclassified lidar surface were compared to the elevation values of the surveyed NVA check points. The RMSE was computed to be 0.058 m (0.192 ft) resulting in an AccuracyZ at the 95% confidence level of 0.115 m (0.376 ft).

The NVA check points were also compared to the elevations of the derived bare earth DEMs. The RMSE was computed to be 0.048 m (0.158 ft) resulting in an AccuracyZ of 0.094 m (0.309 ft) at the 95% confidence level. NVA AccuracyZ has been tested and meets the required 19.6 cm at 95% confidence level using (RMSEz * 1.9600) for both the raw lidar point cloud and derived DEMs, as defined by the National Standards for Spatial Data Accuracy (NSSDA) and herein reported using National Digital Elevation Program (NDEP)/ASPRS Guidelines.

Elevations of the 219 VVA check points were compared to the elevations of the derived bare earth DEMs. The RMSE was computed to be 0.113 m (0.371 ft) and resulted in an AccuracyZ of 0.209 m (0.687 ft) at the 95th percentile. AccuracyZ has been tested on the derived bare earth DEMs and meets the required 29.4 cm (DEM) VVA using the 95th percentile of the absolute value of all vertical errors in all combined vegetation classes as defined by the National Standards for Spatial Data Accuracy (NSSDA); and herein reported using National Digital Elevation Program (NDEP)/ASPRS Guidelines.

LAS files include all data points collected. No points have been removed or excluded. Shaded relief images have been visually inspected for data errors such as pits, border artifacts, and shifting. LiDAR flight lines have been examined to ensure consistent elevation values across overlapping flight lines. The raw point cloud is of good quality and data passes Vertical Accuracy specifications.

Classified LAS files were tested by QSI for both vertical and horizontal accuracy. All data is seamless from one tile to the next, no gaps or no data areas.