2012 FEMA Lidar: Valdez, Alaska

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Bulk download of data files in LAZ format, geographic coordinates, orthometric heights. Note that the vertical datum (hence elevations) of the files here are different than described in this document.

Information on the NOAA Office for Coastal Management (OCM)

The Data Access Viewer (DAV) allows a user to search for and download elevation, imagery, and land cover data for the coastal U.S. and its territories. The data, hosted by the NOAA Office for Coastal Management, can be customized and requested for free download through a checkout interface. An email provides a link to the customized data, while the original data set is available through a link within the viewer.

This graphic displays the footprint for this lidar data set.

Link to data set report.

Link to the QA report.

Using a Optech Gemini LiDAR system, 120 flight lines of highest density (Nominal Pulse Spacing of 1.0 m) were collected over the Valdez area. A total of 6 missions were flown on the following dates: 9-21-2011, two on 9-26-2011, 10-18-2011, 10-28-2011 and 6-18-2012. Four airborne global positioning system (GPS) base stations were used to support the LiDAR data acquisition: 45652650, 83682650, 19112910, and 45652910 located at the Valdez airport. Coordinates and further information is available in the Cordova Post-Flight Aerial Acquisition Report.

The LiDAR data was captured using a twin engine fixed wing aircraft equipped with a LiDAR system. The LiDAR system includes a differential GPS unit and inertial measurement system to provide superior accuracy.

Acquisition parameters:

1. Scanner - Optech ALTM Gemini LIDAR, Leica ALS70

2. Flight Height - 1750 meters above ground level

3. Swath Width - 10 degrees

4. Sidelap - 67%

5. Nominal Point Spacing - 8 points per meter

GPS and IMU processing parameters:

1. Processing Programs and version - Applanix POSPac, version 4.4

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

Point Cloud Processing:

1. Program and version - Optech's Dashmap 5.20

2. Horizontal Datum - NAD83

3. Horizontal Coordinates - UTM zone 6N, in meters.

4. Vertical Datum - NAVD88

5. Geoid Model used to reduce satellite derived elevations to orthometric heights - Geoid09 (Survey Feet).

LIDAR Processing:

1. Processing Programs and versions - Optech's Dashmap version 5.20, Leica's IPAS version 3.1, TerraSolid TerraScan (version 011.018), TerraModeler (version 011.005 and TerraMatch (version 011.015) and Intergraph MicroStation (version.08.05.02.70).

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

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

4. QC (Quality Control) for calibration errors in the dataset. This is accomplished by sampling the data collected accross all flight lines and classify the idividual lines to ground. The software will use the ground-classified lines to compute corrections (Heading, Pitch, Roll, and Scale).

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

6. 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.

7. Aerometric provided Quality Assurance and Quality Control (QAQC) data for this project. Aerometric processed QA/QC points in 'open terrian' 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 QAQC 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 QAQC data, a bias adjustment was determined, and the results were applied to the LIDAR data. A final OCR was performed with a resulting RMSE of 0.055m for the project.

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

9. Final deliverables are generated and output to a client specified PLSS tiling scheme.

The NOAA Office for Coastal Management (OCM) downloaded 64 laz files from the Alaska Division of Geological and Geophysical Surveys data Portal (https://elevation.alaska.gov/). The files contained classified elevation and intensity measurements for the 2012 Valdez data set. The data were in UTM Zone 6 coordinates and NAVD88 (GEOID09) elevations in feet. The data had the following classifications: 1 - Unclassified, 2 - Ground, 7 - Noise, 8 - Model Key Point. OCM processed all points to the Digital Coast Data Access Viewer (DAV). OCM found that several differing values for the vertical accuracy were noted in different fields within the provided metadata and the accompanying reports. Those values have been maintained in this metadata record, as provided in the original metadata. All values for the vertical accuracy found during the OCM processing are:

1. From the AeroMetric metadata - values of 4.5 cm RMSE (Purpose field), 5.5 cm RMSE (Process Step field) and 6.9 cm RMSE (Vertical Accuracy field)

2. From the Elevation Data Quality Assurance Report (Spatial Information Solutions) - 14.4 cm RMSE

3. From the AeroMetric Post-Flight Aerial Acquisition Report - 17.6 cm RMSE

OCM performed the following processing on the data for Digital Coast storage and provisioning purposes:

1. LAStools lasinfo and lasvalidate were run on the laz files to check for errors.

2. LAStools lasinfo was used to convert the global encoding bit from 0 to 1.

3. An internal OCM script was run to check the number of points by classification and by flight ID and the gps and intensity ranges.

4. Internal OCM scripts were run on the laz files to convert from UTM Zone 6 coordinates to geographic coordinates, to convert from NAVD88 elevations to ellipsoid elevations using the GEOID09 model, to convert from feet to meters, to assign the geokeys, to sort the data by gps time and zip the data to database and to http.