2013 NOAA Topographic Lidar: U.S. Virgin Islands (St. Croix, St. John, St. Thomas)

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Converted from FGDC Content Standard for Digital Geospatial Metadata (version FGDC-STD-001-1998) using 'fgdc_to_inport_xml.pl' script. Contact Tyler Christensen (NOS) for details.

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LiDAR points were used to produce the deliverables. | Source Geospatial Form: digital data | Type of Source Media: Hard Drive

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. TerraScan and TerraModeler software packages were then 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.

All ground (ASPRS Class 2) LiDAR data inside of the collected 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 lidar files were received by the NOAA Office for Coastal Management for incorporation into the NOAA Digital Coast. The data consisted of 358 lidar files. The data were in LAS format 1.2 and were in UTM, Zone 20, NAD83, meters coordinates. The data were in Virgin Islands Vertical Datum (VIVD09), meters vertical units. The classifications of the data were: 1 (Unclassified), 2 (Ground), 7 (Noise), 9 (Water), 10 (Ignored Ground, breakline proximity), 17 (Overlap Unclassified), 18 (Overlap Ground), 25 (Overlap Water). For Digital Coast data storage and provisioning purposes, the NOAA OCM performed the following processing: 1. The data were reviewed for any elevation outliers. 2. The data were converted from UTM, Zone 20 coordinates to geographic coordinates. 3. The data were converted from VIVD09 elevations to ellipsoid elevations using Geoid12a. 4. The points that were classified as 25 (Overlap Water) were reclassified to 16 (Overlap Water). 5. The global encoding bit in the las file headers was changed from 0 to 1. 6. The data were converted from las to laz format.