Photo Science, Inc.
Department of Commerce (DOC), National Oceanic and Atmospheric Administration (NOAA), National Ocean Service (NOS), Office for Coastal Management (OCM)
20140829
2013 NOAA Topographic Lidar: US Virgin Islands Digital Elevation Models (DEMs)
Model
https://coast.noaa.gov/dataviewer/#/lidar/search/where:ID=8390
https://coast.noaa.gov/htdata/raster2/elevation/NOAA_USVI_DEM_2013_8390
https://coast.noaa.gov/dataviewer
https://coast.noaa.gov
The United States Virgin Islands Topographic LiDAR Task Order involved collecting and delivering topographic elevation point data derived from multiple return light detection and ranging (LiDAR) measurements on the islands of St. Thomas, St. John, St. Croix and numerous smaller islands and islets in the United States Virgin Islands. The data collected for the project area will exhibit Hydro Flattened DEMs (1m resolution) for inclusion into the NED. The purpose of the data is for use in coastal management decision making, including applications such as flood plain mapping and water rights management. LiDAR was collected at an average of 0.7 meter point spacing for all acquired project areas.
Overall the DEMs were acceptable, but appear oversampled as a result of low ground point density (heavy vegetation), and is not a contractor issue as a 1 m DEM was specified. Incremental improvements to the DEMs were earned through breakline adjustments. Another characteristic of the USVI lidar data that was observed on all islands is the appearance of divots where there is a single tree or a narrow line of trees that lie in areas of open, bare terrain. The cause appeared to be sub-canopy points that were lower than the surrounding land. In most cases these low points were lower than the true ground surface at those locations, but were classified as ground and retained in the point cloud for use in DEM generation. This issue was not addressed during revisions.
Raster DEM files are used to show the Digital Elevation Model of the LAS Class 2 points. Breaklines can be incorporated into
the DEM to show a more representative surface.
20131109
20131210
Ground Condition
Unknown
-65.093469
-64.561957
18.423828
17.670388
ISO 19115 Topic Category
elevation
none
Model
LiDAR
DEM
Raster
Breaklines
Remote Sensing
None
United States Virgin Islands
Saint Thomas
Saint John
Saint Croix
Charlotte Amalie
US
None
None. However, users should be aware that temporal changes may have occurred since this data set was collected and that some parts of the data may no longer represent actual surface conditions. Users should not use the data for critical applications without a full awareness of its limitations.
Precision Aerial Reconnaissance, LLC. acquired the LiDAR for the entire project area. Photo Science performed all LiDAR post-processing and created all required deliverables for the project.
MicroStation Version 8; TerraScan Version 14; TerraModeler Version 14; GeoCue Version 2013.1.45.1; ESRI ArcGIS 10.1;
Global Mapper Version 15.2; ALS Post Processor Version 2.75 Build #25; Windows 7 Operating System
The project area requires LiDAR to be collected on average of 0.7 meter point spacing or better and vertical accuracy of 9.25 centimeters RMSE or better to support 1' contour generation when combined with breaklines.
Bare-earth DEMs were tested by Photo Science, Inc. for vertical accuracy. All data are seamless from one tile to the next, no gaps or no data areas.
Datasets contain complete coverage of tiles.
There is no assessment of the accuracy of the DEMs. However, the horizontal accuracy of the lidar that was collected and used to help create the DEMs was determined. The LiDAR data was compiled to meet a 1 meter horizontal accuracy. The calibration of the LiDAR sensor itself and the calibration process of the data produced by this sensor ensure that this accuracy is met.
1.0
Value stated in meters
There is no assessment of the accuracy of the DEMs. However, the vertical accuracy of the lidar that was collected and used to help create the DEMs was determined. NOAA OCM conducted the vertical accuracy assessment for this data set. Eighty ground control points were collected on all three islands. The following are the number of points collected per island: St. Croix (31), St. John (19), St. Thomas (30). The accuracy specification called for a 9.25 cm Root Mean Square Error (RMSE) for all the islands. St. John and St. Thomas met this specification, however, St. Croix did not. The RMSE values for each island are as follows: St. Croix (14 cm), St. John (7 cm), St. Thomas (8 cm). The all islands RMSE value is 11 cm.
The Quality Assurance Review Report may be viewed at: https://coast.noaa.gov/htdata/lidar1_z/geoid12a/data/3669/supplemental/usvi2013_stc_stj_stt_m3669_qa_report.pdf
The Check Point Survey Report may be viewed at: https://coast.noaa.gov/htdata/lidar1_z/geoid12a/data/3669/supplemental/usvi2013_stc_stj_stt_m3669_chk_pnt_report.pdf
0.11
RMSE in meters of classified LiDAR
Photo Science, Inc.
2014
LiDAR
digital data
Hard Drive
20131109
20131210
ground condition
LiDAR
LiDAR points were used to produce the deliverables.
Applanix + POSPac Mobile Mapping Suite software was used for post-processing of airborne GPS and inertial data (IMU), which is critical to the positioning and orientation of the LiDAR sensor during all flights. POSPac combines aircraft raw trajectory data with stationary GPS base station data yielding a “Smoothed Best Estimate Trajectory (SBET) necessary for additional post processing software to develop the resulting geo-referenced point cloud from the LiDAR missions.
During the sensor trajectory processing (combining GPS and IMU datasets) certain statistical graphs and tables are generated within the Applanix POSPac processing environment which are commonly used as indicators of processing stability and accuracy. This data for analysis include: Max horizontal / vertical GPS variance, separation plot, altitude plot, PDOP plot, base station baseline length, processing mode, number of satellite vehicles, and mission trajectory.
The generated point cloud is the mathematical three dimensional composite of all returns from all laser pulses as determined from the aerial mission. Point clouds were created using the Leica ALS Post Processor software. Laser point data are imported into TerraScan and a manual calibration is performed to assess the system offsets for pitch, roll, heading and scale. At this point this data is ready for analysis, classification, and filtering to generate a bare earth surface model in which the above-ground features are removed from the data set. GeoCue distributive processing software was used in the creation of some files needed in downstream processing, as well as in the tiling of the dataset into more manageable file sizes.
2013
TerraScan and TerraModeler software packages were used for the automated data classification, manual cleanup, and bare earth generation. Project specific macros were developed to classify the ground and remove side overlap between parallel flight lines.
The classes used in the dataset are as follows and have the following descriptions:
Class 1 – Processed, but Unclassified – These points would be the catch all for points that do not fit any of the other deliverable classes. This would cover things like vegetation, buildings, cars, bridges, etc.
Class 2 – Bare earth ground – This is the bare earth surface
Class 7 – Noise – Low or high points, manually and/or automatically identified above or below the surface that could be noise points in point cloud.
Class 9 – Water – Points found inside of inland lake/ponds, rivers or points on the ocean side of any shoreline feature.
Class 10 – Ignored Ground – Points found to be close to breakline features. Points are typically moved to this class from Class 2. This class is ignored during the DEM creation.
Class 17 – Overlap Default (Unclassified) – Points found in the overlap between flight lines. These points are created through automated processing methods and are not cleaned up during manual classification.
Class 18 – Overlap Bare-earth ground – Points found in the overlap between flight lines. These points are created through automated processing, matching the specifications determined during the automated process, that are close to the Class 2 dataset (when analyzed using height from ground analysis)
Class 25 – Overlap Water – Points found in the overlap between flight lines that are located inside hydro features. These points are created through automated processing methods and are not cleaned up during manual classification.
All overlap data was processed through automated functionality provided by TerraScan to classify the overlapping flight line data to approved classes by USGS. The overlap data was classified to Class 17 (Overlap Default) and Class 18 (Overlap Ground). These classes were created through automated processes only and were not verified for classification accuracy. Due to software limitations within TerraScan, these classes were used to trip the withheld bit within various software packages.
The bare earth surface is then manually reviewed to ensure correct classification on the Class 2 (Ground) points. After the bare earth surface is finalized; it is then used to generate all hydro-breaklines through heads-up digitization.
Class 2 LIDAR was used to create a bare earth surface model. The surface model and LAS intensity were then used to heads-up digitize 2D breaklines of inland streams and rivers as well as the ocean shoreline. Inland Ponds and Lakes of 2 acres or greater were also collected.
Elevation values were assigned to all Inland Ponds and Lakes using TerraModeler functionality.
Elevation values were assigned to all Inland Streams and Rivers using Photo Science proprietary software.
Elevation values were assigned to all Coastal Shoreline features using TerraModeler functionality. Z values for the shorelines were assigned based on tidal conditions at the time of acquisition.
All ground (ASPRS Class 2) LiDAR data inside of the Lake Pond and Double Line Drain hydro flattening breaklines were then classified to water (ASPRS Class 9) using TerraScan macro functionality. A buffer of 1 meter was also used around each hydro flattened feature to classify these ground (ASPRS Class 2) points to Ignored ground (ASPRS Class 10). All Lake Pond Island and Double Line Drain Island features were checked to ensure that the ground (ASPRS Class 2) points were reclassified to the correct classification after the automated classification was completed.
LAS data was then run through additional macros to ensure deliverable classification levels matching LAS ASPRS Classification structure. GeoCue functionality was used to ensure correct LAS Version. In house software was used as a final QA/QC check to provide LAS Analysis of the delivered tiles.
The breakline files were translated to ESRI Shapefile format using ESRI conversion tools.
Class 2 LiDAR in conjunction with the hydro breaklines were used to create a 1.0 meter Raster DEM. Using automated scripting routines within ArcMap, an ERDAS Imagine IMG file was created for each tile. Each surface is reviewed using Global Mapper to check for any surface anomalies or incorrect elevations found within the surface.
2014
NOAA OCM received the Digital Elevation Models (DEMs) along with the las points and the hydro-flattened breaklines. Overall the DEMs were acceptable, but appear oversampled as a result of low ground point density (heavy vegetation), and is not a contractor issue as a 1 m DEM was specified. Incremental improvements to the DEMs were earned through breakline adjustments. Another characteristic of the USVI lidar data that was observed on all islands is the appearance of divots where there is a single tree or a narrow line of trees that lie in areas of open, bare terrain. The cause appeared to be sub-canopy points that were lower than the surrounding land. In most cases these low points were lower than the true ground surface at those locations, but were classified as ground and retained in the point cloud for use in DEM generation. This issue was not addressed during revisions. For further information, the QA Review Report may be accessed here: https://coast.noaa.gov/htdata/lidar1_z/geoid12a/data/3669/supplemental/usvi2013_stc_stj_stt_m3669_qa_report.pdf
2014
Raster
Universal Transverse Mercator
20
0.99960000
-63.00000000
0.0
500000.00000000
0.0
coordinate pair
0.01
0.01
meters
North American Datum of 1983
Geodetic Reference System 1980
6378137.000000
298.257222
Local Mean Sea Level
0.01
meters
Explicit elevation coordinate included with horizontal coordinates
ERDAS .IMG files with a 1 meter pixel. No Data values outside of the project area are represented with -3.4028235e+038.
All deliverables meet specifications in contract. LAS Files meet ASPRS Classification Standards.
NOAA Office for Coastal Management
mailing and physical
2234 South Hobson Avenue
Charleston
SC
29405-2413
843-740-1202
coastal.info@noaa.gov
Downloadable Data
Any conclusions drawn from the analysis of this information are not the responsibility of the PhotoScience, the Office for Coastal Management, or its partners.
This data can be obtained on-line at the following URL: https://coast.noaa.gov/dataviewer
20170925
NOAA Office for Coastal Management
mailing and physical
2234 South Hobson Avenue
Charleston
SC
29405-2413
843-740-1202
coastal.info@noaa.gov
FGDC Content Standards for Digital Geospatial Metadata
FGDC-STD-001-1998