Data Management Plan

TerraPoint surveyed and created this data for the Puget Sound LiDAR Consortium under contract. The area surveyed is approximately 167 square miles and covers a northwest portion of Snohomish County, WA.

All data was collected during ideal conditions (leaf-off).

The LAS files were derived from all returns ASCII files contain the X,Y,Z values of all the LiDAR returns collected during the survey mission. The GPS time, classification, scan angle, intensity and return numbers of each point

were preserved in the conversion from ASCII to LAS. The LAS files are classified into the following ASPRS classes: (1) Unclassified (2) Bare Earth. Ground and water points are included in Class 2 (Bare Earth). Futher details are

available in the Process Steps below. The NOAA Office for Coastal Management noticed that some intensity values are 0, so be aware before using the intensity information.

This dataset was flown in 2003 with a 50% overlap between flight lines. Due to the overlap the nominal point spacing of the dataset is 1.0 meter.

Process Steps:

• Acquisition. Lidar data were collected in leaf-off conditions (approximately 1 November - 1 April) from a fixed-wing aircraft flying at a nominal height of 1,000 meters above ground surface. Aircraft position was monitored by differential GPS, using a ground station tied into the local geodetic framework. Aircraft orientation was monitored by an inertial measurement unit. Scan angle and distance to target were measured with a scanning laser rangefinder. Scanning was via a rotating 12-facet pyramidal mirror; the laser was pulsed at 30+ KHz, and for most missions the laser was defocussed to illuminate a 0.9m-diameter spot on the ground. The rangefinder recorded up to 4 returns per pulse. Flying height and airspeed were chosen to result in on-ground pulse spacing of about 1.5 m in the along-swath and across-swath directions. Most areas were covered by two swaths, resulting in a nominal pulse density of about 1 per square meter.
• Processing. GPS, IMU, and rangefinder data were processed to obtain XYZ coordinates of surveyed points. For data acquired after January 2003 (NW Snohomish, Mt Rainier, Darrington, and central Pierce projects), survey data from areas of swath overlap were analysed to obtain best-fit in-situ calibration parameters that minimize misfit between overlapping swaths. This reduces vertical inconsistency between overlapping swaths by about one-half. Heights were translated from ellipsoidal to orthometric (NAVD88) datums via GEOID99
• ASCII file generation All Point returns with all their attributes were directly exported into ASCII files. These were first divided into USGS quarter quads (3.25 minute by 3.25 minute) and then in 25 tiles per quarter quad.
• 2013-02-01 00:00:00 - The NOAA Office for Coastal Management (OCM) received topographic files in ASCII .TXT format. The files contained lidar elevation measurements. The data were received in Washington State Plane North Zone 4601, NAD83 coordinates and were vertically referenced to NAVD88 using the Geoid99 model. The vertical units of the data were feet. OCM performed the following processing for data storage and Digital Coast provisioning purposes: 1. The ASCII .TXT files were parsed and converted to LAS version 1.2 using LAStools' txt2las tool. 2. Bad elevations were filtered and removed from many tiles across the data set on a tile by tile basis using LASTools' las2las tool. 3. The topographic las files were converted from orthometric (NAVD88) heights to ellipsoidal heights using Geoid99. 4. The topographic las files were converted from a Projected Coordinate System (WA SP North) to a Geographic Coordinate system (NAD 83). 5. The topographic las files' vertical units were converted from feet to meters. 6. The topographic las files' horizontal units were converted from feet to decimal degrees.

This data can be obtained on-line at the following URL:

https://coast.noaa.gov/dataviewer/#/lidar/search/where:ID=1462

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