2011 Puget Sound LiDAR Consortium (PSLC) Topographic LiDAR: Quinault River Basin

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This graphic shows the lidar coverage for the Quinault collected in 2011 in Grays Harbor

county Washington.

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.

Partial upload of Positional Accuracy fields only.

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Acquisition.

The LiDAR survey utilized a Leica ALS50-II sensor in a Cessna Caravan 208B.

Depending on acquisition day, weather, and terrain, the Leica systems were set to

acquire 105,000 laser pulses per second (i.e.105 kHz pulse rate) and flown at 900

meters above ground level (AGL), capturing a scan angle of +/- 14 degrees from

nadir. These settings were developed to yield points with an average native

pulse density of 8 pulses per square meter over terrestrial surfaces. It is not

uncommon for some types of surfaces to return fewer pulses than the laser

originally emitted. These discrepancies between 'native' and 'delivered' density will

vary depending on terrain, land cover, and the prevalence of water bodies.

All areas were surveyed with an opposing flight line side-lap of more than 60%

(less than 100% overlap) to reduce laser shadowing and increase surface

laser painting. The Leica laser systems allow up to four range

measurements (returns) per pulse, and all discernable laser returns

were processed for the output dataset.

To accurately solve for laser point position (geographic coordinates x, y, z)

the positional coordinates of the airborne sensor and the attitude of the

aircraft were recorded continuously throughout the LiDAR data collection

mission. Aircraft position was measured twice per second (2 Hz) by an onboard

differential GPS unit. Aircraft attitude was measured 200 times per second

(200 Hz) as pitch, roll and yaw (heading) from an onboard inertial measurement

unit (IMU). To allow for post-processing correction and calibration,

aircraft/sensor position and attitude data are indexed by GPS time.

1. Resolved kinematic corrections for aircraft position data using kinematic

aircraft GPS and static ground GPS data.

Software - Waypoint GPS v.8.10, Trimble Business Center 2.6

2. Developed a smoothed best estimate of trajectory (SBET) file that blends

post-processed aircraft position with attitude data. Sensor head position and

attitude were calculated throughout the survey. The SBET data were used

extensively for laser point processing.

Software - IPAS TC v.3.1

3. Calculated laser point position by associating SBET position to each laser

point return time, scan angle, intensity, etc. Created raw laser point cloud

data for the entire survey in *.las (ASPRS v. 1.2) format.

Software - ALS Post Processing Software v.2.74, Corpscon 6

4. Imported raw laser points into manageable blocks (less than 500 MB) to

perform manual relative accuracy calibration and filter for pits/birds. Ground

points were then classified for individual flight lines (to be used for

relative accuracy testing and calibration).

Software - TerraScan v.12.004

5. Using ground classified points per each flight line, the relative

accuracy was tested. Automated line-to-line calibrations were then performed

for system attitude parameters (pitch, roll, heading), mirror flex (scale)

and GPS/IMU drift. Calibrations were performed on ground classified points

from paired flight lines. Every flight line was used for relative accuracy

calibration.

Software - TerraMatch v.12.001

6. Position and attitude data were imported. Resulting data were classified

as ground and non-ground points. Statistical absolute accuracy was assessed

via direct comparisons of ground classified points to ground RTK survey data.

Data were then converted to orthometric elevations (NAVD88) by applying a

Geoid03 correction. Software: TerraScan v.12.004, TerraModeler v.12.002

7. Bare Earth models were created as a triangulated surface and exported as

ArcInfo ASCII grids at a 3-foot pixel resolution. Highest Hit models were

created for any class at 3-foot grid spacing and exported as ArcInfo ASCII

grids.

Software - TerraScan v.12.004, ArcMap v.10.0, TerraModeler v.12.002

The NOAA Office for Coastal Management (OCM) downloaded topographic files in LAZ format from PSLC's website.

The files contained lidar easting, northing, elevation, intensity, return number, class, scan angle

and GPS time measurements; the data was received in state plane Washington (in feet) and vertical coordinates were

referenced to NAVD88 in feet using the Geoid03 model.

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

1. The All-Return LAZ files were checked for bad elevations

2. The laz files were converted from a Projected Coordinate System (SP 4602) to a Geographic Coordinate system (NAD83)

3. The laz files were then converted to ellipsoidal vertical units in meters using the geoid03 conversion.