2011 ARRA Lidar: Hidalgo County (TX)

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This graphic shows the lidar coverage of the Hidalgo County, Texas from 2011 to support ARRA of 2009.

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 Cessna 310, fixed wing aircraft equipped with a LiDAR system. The LiDAR system includes a differential GPS unit and inertial measurement system to provide superior positional accuracy.

Acquisition parameters:

1. Flight Height - 2500 meters above mean terrain

2. Swath Width - 34 degrees

3. Sidelap - 30%

4. Nominal Post Spacing - 1.5 meters

GPS and IMU processing parameters:

1. Maximum baseline length - Not greater than 40 kilometers.

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

3. Maximum positional RMS of trajectory during LiDAR collection - 0.05 meters

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

Point Cloud Processing:

1. Horizontal Datum - NAD83(NSRS2007)

2. Horizontal Coordinates - Universal Transverse Mercator, Zone 14, 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 via 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 or anomalies 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 points by flightline to compute corrections (Heading, Pitch, Roll, and Scale).

4. Orientation corrections (i.e. Calibration corrections) are 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 0.086 meters for the project.

7. Each tile is reviewed for accuracy and consistency of the macro ground classification.

8. 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.

9. Final deliverables are generated and output to a client specified 1500 meters by 1500 meters tiling scheme.

The NOAA Office for Coastal Management (OCM) downloaded topographic files (point clouds) in LAZ format from an USGS ftp site. The data was received in UTM Zone 14 North (in meters) and vertical coordinates were referenced to NAVD88 in meters using the Geoid09 model. OCM performed the following processing for data storage and Digital Coast provisioning purposes:

1. The All-Return LAZ files were checked for erroneous outliers removed.

2. The LAZ files were converted from a UTM coordinates to Geographic Coordinates (decimal degrees), then converted to ellipsoidal vertical units in meters with respect to the Geoid09.

3. Overlapping tiles (42) exist on the county boundary between Hidalgo and Willacy counties. These were decidedly left as is in order to extend past county boundaries for individual county requests. These are duplicate points between projects as they are the same acquired lidar points.