2009 PSLC-USGS Topographic LiDAR: Wenatchee

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This graphic shows the lidar coverage of Chelan and Douglas counties, Washington area collected in 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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Acquisition.

The lidar survey uses a Leica ALS50 Phase II laser system. For the Wenatchee USGS survey

area, the sensor scan angle +/- 14 degrees from nadir with a pulse rate designed to yield an

average native density (number of pulses emitted by the laser system) of more than 8 points

per square meter over terrestrial surfaces. All survey areas were surveyed with an opposing

flight line side-lap of more than 50% (less than 100% overlap) to reduce laser shadowing and

increase surface laser painting. The Leica ALS50 Phase II system allows up to four range

measurements (returns) per pulse, and all discernible laser returns were processed for the

output dataset. It is not uncommon for some types of surfaces (e.g. dense vegetation or water)

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.

To accurately solve for laser points 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, 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.

Resolved kinematic corrections for aircraft position data using kinematic aircraft GPS and

static ground GPS data.

Software - Waypoint GPS v.8.10, Trimble Geomatics Office v.1.62

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 v.1.4

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 v1.1) format.

Software: ALS Post Processing Software v.2.69

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.9.001

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.9.001

Position and attitude data were imported. Resulting data were classified as ground and nonground

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. Ground models were created as a

triangulated surface and exported as ArcInfo ASCII grids at a 3-foot pixel resolution.

Software - TerraScan v.9.001, ArcMap v.9.3, TerraModeler v.9.001

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.