2015 Univ of TX BEG Topobathy Lidar: Shamrock Cove, Texas (Mustang Island & Corpus Christi Bay)

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Information on the NOAA Office for Coastal Management (OCM)

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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.

This graphic displays the footprint for this lidar data set.

raw lidar data from Chiroptera

20150130A 20150205

Ground GPS base stations

Preparation and Data acquisition

Chiroptera system is installed in aircraft. GPS to laser offset values are measured using a survey grade Total Station (if first time installation). System is turned on using ground AC power connection to the aircraft for system check. Aircraft GPS receiver is turned on to start data collection. The pre-determined flight plan is uploaded to the Flight Management software. Ground GPS base stations are setup on geodetic reference points (with known precise Northing, Easting, and Elevation information) in or near the survey area. GPS receivers are set for continuous 1 second data collection rate. Aircraft GPS and Base GPS information needs to overlap each other for the duration of the survey flight. Aircraft takes off to begin the survey mission. Pilot follows the flight altitude, speed and the flight lines as directed by the flight plan. Raw laser point cloud data is collected with external solid state hard drives in the Chiroptera. High resolution raw images are collected using integrated medium format camera. VGA low resolution images are collected for operator and post-processing reference. GPS and attitude (INS) information is collected on an external storage device. Airborne survey is completed after all flight lines are flown.

Data Download and Preliminary Field Processing

All laser data and raw image files are downloaded to the field computer using its internal drive enclosures. GPS and INS data are downloaded using USB3.0 connections to the field computer. Preliminary GPS processing is completed by merging base GPS receiver with the remote to create a GPS trajectory (GrafNav). The preliminary GPS trajectory is combined with attitude information in AEROoffice to create a 7-parameter (TXYZ,roll,pitch,yaw) navigation file. The navigation solution is used to reference each laser pulse return with the 7-paramater information in LSS. Laser point cloud data is output by flight line in multiple segments. Point cloud data is examined to determine quality of the data coverage (i.e. sufficient overlap of flight lines and point spacing).

Post-Processing

Upon return from the survey area, all files are transferred from the field computer to an in-house server. Compute base station coordinates using National Geodetic Survey's (NGS) Online Positioning User Service (OPUS). Setup project in AEROoffice software and covert Chiroptera GPS files to binary Novatel GPS files. Convert aircraft GPS file and base station GPS files to GrafNav compatible format. Compute merged aircraft trajectory using GrafNav software. Solutions for base station coordinates and aircraft trajectories are in NAD83. Combine precise trajectories with aircraft attitude information in AEROoffice to create final precise 7-parameter navigation file (TXYZ,roll,pitch,yaw). Laser point data are generated in AHAB processing software Lidar Survey Studio (LSS) combining navigation file information and laser data. LSS also requires a calibration, processing settings, and system configuration files.

LSS parameters are adjusted to minimize noisy data output. A configuration file is prepared by setting amplitude thresholds and backscatter threshold values. A water-refraction value based on salinity is computed to provide optimum performance (1.3429). The select map option is utilized to automatically determine the water surface elevation (within LSS). After initial processing, waveform information is analyzed to determine if the laser returns are being classified properly.

Bathymetric laser-point data were output from LSS in LAS v1.2 format (a binary file format). A condition is set in LSS to output data in the proper UTM zone and hemisphere. The resultant points are referenced to the Geographic NAD83 horizontal datum and height above the NAD83 ellipsoid. Using the TerraScan utility of MicroStation, flight line segment files were concatenated and Class 6 (shallow bathymetric returns) and Class 7 (bottom/seafloor) were extracted. The 2012A geoid model was used to adjust the elevation data from ellipsoidal to orthometric heights (NAVD88) using a LAStools script called lasheight.

The NOAA Office for Coastal Management (OCM) received 2 files (one for topo and one for bathy) in las format from UT BEG. The files contained elevation and intensity measurements along the coast of Texas. The data were in UTM Zone 14 NAD83 coordinates and NAVD88 (Geoid12A) elevations in meters The data were classified as: 6 (bathy/bathy vegetation), 7 (bathy), 9 (ground), 13 (low vegetation), 14 (medium vegetation), 15 (high vegetation) . OCM performed the following processing on the data for Digital Coast storage and provisioning purposes:

1. The LAStools software scripts lasinfo and lasvalidate, were run on the las files to check for errors.

2. The LAStools software script las2las was run to convert the classifications of:

Class 6 (bathy/bathy vegetation) to Class 14 (bathy/bathy vegetation)

Class 7 (bathy) to Class 26 (bathy)

Class 9 (ground) to Class 2 (ground)

Class 13, 14, 15 (low/medium/high vegetation) to Class 1 (unclassified) - these classes were converted due to the fact that many points with these classifications were actually structures.

3. Internal OCM scripts were run on the las files to convert from UTM Zone 14 NAD83 coordinates to geographic NAD83 coordinates, from orthometric (NAVD88) elevations to ellipsoid elevations using the Geoid 12A model, to assign the geokeys, and zip the data to database and to http.