2012 USGS Lidar: Juneau (AK)

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This graphic shows the lidar coverage for the 2012 USGS lidar project for Juneau (AK).

Date that the source FGDC record was last modified.

Converted from FGDC Content Standards 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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The LiDAR data was captured using AeroMetric's twin-engine fixed wing aircraft equipped with an Optech LiDAR system. The LiDAR systems includes a differential GPS unit and inertial measurement system to provide superior accuracy.

Acquisition parameters:

1. Flight Height - 1500 meters or lower above mean terrain

2. Swath Width - 28 degrees

3. Sidelap - 55%

4. Nominal Post Spacing - 1.0 meters

GPS and IMU processing parameters

1. Maximum baseline length - Not greater than 100 kilometers.

2. Number of base stations during LiDAR collection - A minimum of 1.

3. Maximum positional RMS of trajectory during LiDAR collection - 0.10 meters

4. IMU processing monitored for consistency and smoothness - Yes.

Point Cloud Processing:

1. Horizontal Datum - NAD83

2. Horizontal Coordinates - Universal Transverse Mercator, Zone 8, in meters.

3. Vertical Datum - NAVD88

4. Geoid Model used to reduce satellite derived elevations to orthometric heights - NGS Geoid09.

LiDAR Processing:

1. Point Cloud data is imported to TerraScan in a Microstation V8 (V) CAD environment on a specified 1500 meter by 1500 meter tiling scheme.

2. Analyze the data for overall completeness and consistency. This is to ensure that there are no voids in the data collection.

3. Inspect for calibration errors in the dataset using the TerraMatch software. This is accomplished by sampling the data collected across all flight lines and classify the individual lines to ground. The software will use the ground-classified lines to compute corrections (Heading, Pitch, Roll, and Scale).

4. Orientation corrections (i.e. Calibration corrections) are then applied (if needed) to the entire dataset.

5. Automatic ground classification is performed using algorithms with customized parameters to best fit the project area. Several areas of varying relief and planimetric features were inspected to verify the final ground surface.

6. AeroMetric, Inc. provided Quality Assurance and Quality Control (QA/QC) data for this project. AeroMetric captured QA/QC points in 'open terrain' land cover category that were used to test the accuracy of the LiDAR ground surface. TerraScan's Output Control Report (OCR) was used to compare the QA/QC data to the LiDAR data. This routine searches the LiDAR dataset by X and Y coordinate, finds the closest LiDAR point and compares the vertical (Z) values to the known data collected in the field. Based on the QA/QC data, a bias adjustment was determined, and the results were applied (if necessary) to the LiDAR data. A final OCR was performed with a resulting RMSE of 10.7 cm for the project.

7. After the LiDAR data is finalized for vertical placement, a macro is run via TerraScan to output a dataset generated on a per swath basis as part of the final deliverables. All points of the swath are reclassified to class 0 during this step.

8. Each tile is reviewed for accuracy and consistency of the macro ground classification. During this phase, MicroStation is used to generate line work representing water bodies and rivers. Separate line work is also placed in instances where overpasses have blocked enough valid ground returns or water gave too few ground returns to reasonably portray the ground surface. A proprietary in-house software program is then run to drape the river line work in a flowing fashion. Contours are generated on the river breaklines to review monotonicity of the draped line work.

9. Once the automatic processing and the testing of LiDAR is complete, AeroMetric meticulously reviews the generated bare-earth surface data to ensure that proper classification was achieved as part of a Quality Control process.

10. Final deliverables are generated and output to a client specified 1500 meter by 1500 meter tiling scheme.

The NOAA Office for Coastal Management (OCM) received the files in laz format via an FTP online repository. The files contained lidar elevation and intensity measurements. The data were in UTM Zone 8, NAVD88 (orthometric) heights in meters. OCM performed the following processing for data storage and Digital Coast provisioning purposes:

1. The data were converted from UTM coordinates to geographic coordinates.

2. The data were converted from NAVD88 (orthometric) heights in meters to GRS80 (ellipsoid) heights in meters using Geoid 09.

3. The LAS data were sorted by latitude and the headers were updated.

4. Erroneous elevations were removed.