2015 WA DNR Lidar DEM: Hood Canal, WA

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Bulk download of data files in GeoTiff format, WA State Plane South NAD83(HARN) US survey feet coordinates and orthometric heights in feet.

Link to the GeoTerra Technical Lidar Report from the Washington Lidar Portal.

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.

Lidar Acquisition and Survey Control

GeoTerra, Inc. acquired the LiDAR sensor data on the 15th, 16th and 17th of February 2015. A system calibration was performed prior to the project execution. Weather conditions during time of flight were fair with intermittent cloud cover and some moisture in the air. Pitch and roll were less than 3 degrees for all strips acquired. Real time data was monitored closely to review any errors and gaps prior to de-mobilization from the project site.

During the aerial LiDAR missions, the Airborne GNSS (AGNSS) technique was employed which entails obtaining the X,Y,Z coordinates of the laser during the aerial acquisition. The data collected during the flight is post-processed into a Smoothed Best Estimate of Trajectory (SBET) binary file of the laser trajectory which is the combined processed data from both GNSS satellite data and Inertial Motion Unit (IMU) data and is used along with the ground control points to geo-reference the laser point cloud during the mapping process.

The LiDAR data was acquired utilizing an Optech Orion H sensor with integrated Applanix POS AV GNSS/IMU system mounted in a Cessna 180 aircraft. During the flights the receiver on board the aircraft logged GNSS data at 1 Hz interval and IMU data at 200 Hz interval. The LiDAR acquisition flights occurred on 15, 16, 17-Feb-2015 with two separate flights on each of the three days.

After the flight, the GNSS and IMU data was post-processed using NovAtel’s Waypoint Products Group software package Inertial Explorer Version 8.60.4131. The GNSS data was processed using a differential GNSS technique utilizing Washington State Reference Network (WSRN) Continuously Operating reference Stations (CORS) for the ground stations. CORS sites CUSH and/or ELSH were utilized. The published (22-May 2014) WSRN NAD83(2011)(Epoch 2010.0) values were held fixed to control the AGNSS trajectory. The processed GNSS data were then combined with the IMU data using a loosely coupled technique.

Lever arm offsets between the IMU and the L1 phase center of the aircraft antenna were measured and held fixed as follows: x=-0.075, y=-0.160, z=1.054 m (x-right, y-fwd, z-up). The lever arm from the IMU to the mirror were held fixed at the internal Optech provided values of x=-0.051, y=-0.153, z=0.003 m (x-right, y-fwd, z-up, IMU->Mirror). This resulted in a precise trajectory of the laser that was output as an NAD83(2011)(Epoch 2010.0) SBET file with data points each 1/200 of a second.

Laser Point Post-Processing

During the aerial LiDAR missions, the Airborne GNSS (AGNSS) technique was employed which entails obtaining the X,Y,Z coordinates of the laser during the aerial acquisition. The data collected during the flight is post-processed into a Smoothed Best Estimate of Trajectory (SBET) binary file of the laser trajectory which is the combined processed data from both GNSS satellite data and Inertial Motion Unit (IMU) data and is used along with the ground control points to geo-reference the laser point cloud during the mapping process.

The LiDAR data was acquired utilizing an Optech Orion H sensor with integrated Applanix POS AV GNSS/IMU system. During the flights the receiver on board the aircraft logged GNSS data at 1 Hz interval and IMU data at 200 Hz interval. The LiDAR acquisition flights occurred on 15, 16, 17-Feb-2015 with two separate flights on each of the three days.

After the flight, the GNSS and IMU data was post-processed using NovAtel’s Waypoint Products Group software package Inertial Explorer Version 8.60.4131. The GNSS data was processed using a differential GNSS technique utilizing Washington State Reference Network (WSRN) Continuously Operating reference Stations (CORS) for the ground stations. CORS sites CUSH and/or ELSH were utilized. The published (22-May 2014) WSRN NAD83(2011)(Epoch 2010.0) values were held fixed to control the AGNSS trajectory. The processed GNSS data were then combined with the IMU data using a loosely coupled technique.

Lever arm offsets between the IMU and the L1 phase center of the aircraft antenna were measured and held fixed as follows: x=-0.075, y=-0.160, z=1.054 m (x-right, y-fwd, z-up). The lever arm from the IMU to the mirror were held fixed at the internal Optech provided values of x=-0.051, y=-0.153, z=0.003 m (x-right, y-fwd, z-up, IMU->Mirror). This resulted in a precise trajectory of the laser that was output as an NAD83(2011)(Epoch 2010.0) SBET file with data points each 1/200 of a second.

Raw range data from the sensor was decoded using Optech’s LMS software. Instrument corrections were applied to the laser ranges and scan angles, and then the range files were split into the separate flight lines. The laser point computation uses the results of decoding, description of the instrument and location of the aircraft (from the SBET file) as input data and calculates the coordinates of points for each laser pulse from the sensor.

Relative and Absolute Adjustment

Relative and absolute adjustment of all strips was accomplished using Optech’s LMS software. The software performs automated extraction of planar surfaces from the cloud of points according to specified parameters per project. Tie plane determination establishes the correspondence between planes in overlapping flight lines. All plane centers of all lines that form a block are sorted into a grid. Planes from overlapping flight lines, co-located to within an acceptable tolerance are then tested for correspondence.

A set of appropriate tie planes is selected for the self-calibration. Selection criteria are size and shape, number of laser points, slope, orientation with respect to flight direction, location within the flight line and fitting error. All these criteria have an effect as they determine the geometry of the adjustment. Self-Calibration parameters are then calculated. After they are retrieved they are used to re-calculate the laser point coordinates (x,y,z). The planar surfaces are re-calculated as well for a final adjustment.

Point to plane analysis was performed to assess the internal fit of the data block. For each tie plane, the mean values are computed for each flight line that covers the tie plane. Mean values of the point to plane distances are plotted over scan angle.

After a tight relative fit was achieved, an absolute vertical offset was calculated using surveyed control points. The algorithm computes an average value for the height differences for all control points by comparison to the laser points within a specified radius around the control point. Calculations were performed on 15 control points.

Point Cloud Classification

Once the absolute point cloud adjustment was achieved with desired accuracy, all strips were exported from Optech LMS into LAS format. Data in LAS format was first automatically classified followed by strict QC procedures. The entire area was cut into working tiles of a manageable size and manually checked and edited using LP360 software to correct any misclassification using the following methods:

i. Selected boxes of rotating 3D point clouds, viewed with color-coded classification points.

ii. Point clouds viewed in profile view

iii. Temporary creation of TIN over ground points to assist in identifying points incorrectly classified as ground.

Following classes were delineated in the process of classification:

01_Unclassified - Temporary (cars, debris, etc.)

02_Ground

03_Low Vegetation - vegetation level that falls within 0 - 10 ft from the ground

04_Medium Vegetation - vegetation level that falls within 10 - 20 ft from the ground

05_High Vegetation - vegetation level that falls within 20 ft and above ground

06_Buildings and Associated Structures

09_Water - points reflected off water bodies

10_Unclassified - Permanent (fences, poles, guardrails, bridges, etc.)

Final, classified points were trimmed to the project boundary buffered by 100 feet and cut into final corridor delivery tiles to match the orthophoto delivery tile scheme.

GIS format: Raster Grid of ground surface in ArcGIS format

The NOAA Office for Coastal Management (OCM) downloaded 11 raster DEM files in GeoTiff format from the Washington Lidar Portal. The data were in Washington State Plane South NAD83(HARN), US survey feet coordinates and NAVD88 (Geoid12A) elevations in feet. The bare earth raster files were at a 3 feet grid spacing. No metadata record was provided with the data. This record is populated with information from the GeoTerra technical report downloaded from the Washington Dept. of Natural Resources Washington Lidar Portal.

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

1. Used internal an script to assign the EPSG codes (Horizontal EPSG: 2927 and Vertical EPSG: 6360) to the GeoTiff formatted files.

2. Copied the files to https.