2018 TWDB Lidar: Coastal Texas

The Texas Water Development Board (TWDB) in cooperation with their project partners tasked Fugro Geospatial, Inc. (Fugro) under the Department of Information Resources (DIR) Geographic Information Systems (GIS) Hardware, Software and Services contract also known as the Texas Strategic Mapping (StratMap) Contract to acquire high resolution elevation data and associated products from airborne lidar systems during the 2017-2018 leaf-off season. The StratMap Program promotes inter-governmental collaboration and partnerships to purchase geospatial data products that provide cost savings and project efficiencies. Both the StratMap Program and the StratMap Contract are administered by the Texas Natural Resources Information System (TNRIS), a division of TWDB. Project partners include: Houston-Galveston Area Council (H-GAC), Harris County Flood Control District (HCFCD), and the United States Geological Survey (USGS). This Coastal Texas project consists of approximately 9,758 DO4Q tiles and is located on the Texas Coast covering much of Orange to Matagorda County along with Harris County and the surrounding area. The project includes large metropolitan areas as well as coastal areas. The Urban and Coastal AOIs consist of approximately 4.045 square miles and were acquired between January 12 and March 22, 2018 utilizing both Riegl LMS-Q680i and Riegl LMS-Q780 sensors; collecting multiple return x, y, and z as well as intensity data. Specialized in-house and commercial software processes the native lidar data into 3-dimensional positions that can be imported into GIS software for visualization and further analysis. The data were delivered with the horizontal datum of North American Datum of 1983 (NAD83, 2011) in meters and the vertical datum is the North American Vertical Datum of 1988 (NAVD88) in meters realized with GEOID12B.

The NOAA Office for Coastal Management (OCM) downloaded this data set from this TNRIS site:

https://data.tnris.org/collection/b5bd2b96-8ba5-4dc6-ba88-d88133eb6643

These files were processed to the Data Access Viewer (DAV) and https. The total number of files downloaded and processed was 9071.

In addition to these lidar point data, the bare earth Digital Elevation Models (DEM) created from the lidar point data are also available. These data and the breaklines are available for download at the links provided in the URL section of this metadata record.

Data products generated from this project will be used for floodplain management and planning, feature extraction, water quality modeling, stream restoration potential analysis, change detection and emergency management services and will be made available in the public domain through TNRIS.

N/A

The following are the USGS lidar fields in JSON:

{

"ldrinfo" : {

"ldrspec" : "USGS-NGP Base Lidar Specification v1.2",

"ldrsens" : "Riegl LMS-Q680i",

"ldrmaxnr" : "7",

"ldrnps" : "? 0.5",

"ldrdens" : "? 4",

"ldranps" : "? 0.5",

"ldradens" : "? 4",

"ldrfltht" : "991",

"ldrfltsp" : "140",

"ldrscana" : "60",

"ldrscanr" : "100",

"ldrpulsr" : "250",

"ldrpulsd" : "3",

"ldrpulsw" : "0.8994",

"ldrwavel" : "1550",

"ldrmpia" : "1",

"ldrbmdiv" : "? 0.5",

"ldrswatw" : "825",

"ldrswato" : "31",

"ldrcrs" : "NAD 1983 2011 UTM Zone 15N Meters",

"ldrgeoid" : "National Geodetic Survey (NGS) GEOID12B"

},

"ldrinfo" : {

"ldrspec" : "USGS-NGP Base Lidar Specification v1.2",

"ldrsens" : "Riegl LMS-Q780i-Agg",

"ldrmaxnr" : "7",

"ldrnps" : "? 0.71",

"ldrdens" : "2",

"ldranps" : "? 0.5",

"ldradens" : "? 4",

"ldrfltht" : "991",

"ldrfltsp" : "140",

"ldrscana" : "60",

"ldrscanr" : "100",

"ldrpulsr" : "250",

"ldrpulsd" : "3",

"ldrpulsw" : "0.8994",

"ldrwavel" : "1550",

"ldrmpia" : "1",

"ldrbmdiv" : "? 0.25",

"ldrswatw" : "1150",

"ldrswato" : "60",

"ldrcrs" : "NAD 1983 2011 UTM Zone 15N Meters",

"ldrgeoid" : "National Geodetic Survey (NGS) GEOID12B"

},

"ldraccur" : {

"ldrchacc" : "RMSEx = 0.189 m; RMSEy = 0.186 m",

"rawnva" : "N/A",

"rawnvan" : "N/A",

"clsnva" : "0.048",

"clsnvan" : "0.049",

"clsvva" : "0.062",

"clsvvan" : "0.059"

},

"lasinfo" : {

"lasver" : "1.4",

"lasprf" : "6",

"laswheld" : "There were no withheld points identified in this project. All points were used in the classification.",

"lasolap" : "Swath "overage" points were identified in these files using the standard LAS overlap bit.",

"lasintr" : "16 bit",

"lasclass" : {

"clascode" : "1",

"clasitem" : "Processed, but unclassified"

},

"lasclass" : {

"clascode" : "2",

"clasitem" : "Bare-earth Ground"

},

"lasclass" : {

"clascode" : "3",

"clasitem" : "Low Vegetation (0.01m to 1.00m above ground)"

},

"lasclass" : {

"clascode" : "4",

"clasitem" : "Medium Vegetation (1.01m to 3.00m above ground)"

},

"lasclass" : {

"clascode" : "5",

"clasitem" : "High Vegetation (greater than 3.01m above ground)"

},

"lasclass" : {

"clascode" : "6",

"clasitem" : "Building"

},

"lasclass" : {

"clascode" : "7",

"clasitem" : "Low Point (noise)"

},

"lasclass" : {

"clascode" : "9",

"clasitem" : "Water"

},

"lasclass" : {

"clascode" : "10",

"clasitem" : "Ignored Ground"

},

"lasclass" : {

"clascode" : "14",

"clasitem" : "Culverts"

},

"lasclass" : {

"clascode" : "17",

"clasitem" : "Bridge Decks"

}

}}

Any conclusions drawn from the analysis of this information are not the responsibility of the TWDB or its partners, NOAA, the Office for Coastal Management or its partners.

Data is available online for bulk and custom downloads.

None

Users should be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations.

POSGNSS 5.2; POSPac 8.0; RiProcess 1.8.3; RiWorld 5.0.2; RiAnalyze 6.2; RiServer 1.99.5; Microstation 8.5.2.55 and MicroStation CONNECT 10.00.00.25; TerraScan 018.008; TerraModeler 018.002; Lasedit 1.36.01; GeoCue 2014.1.21.5; ArcMap 10.3; Global Mapper 17; ERDAS Imagine 2016; PhotoShop CS8; Fugro proprietary software; Windows 7 64-bit Operating System

\\triton\lidar\17004800_TNRIS_CoastalTX_Lidar\5_4_5_Delivery\Pilot\DEM_Raster

\\triton\lidar\17004800_TNRIS_CoastalTX_Lidar\5_4_5_Delivery\Pilot\Hydro_Flattened_Breaklines

\\triton\lidar\17004800_TNRIS_CoastalTX_Lidar\5_4_5_Delivery\Pilot\Intensity_Images\*.tif/tfw

\\triton\lidar\17004800_TNRIS_CoastalTX_Lidar\5_4_5_Delivery\Pilot\LAS_Point_Cloud\*.las

During lidar data collection the airborne GPS receiver was collecting data at 2 Hz frequency and the Dilution of Precision (PDOP) was monitored. GPS base stations were also running at the operational airports and were recording data at 1 Hz. The airborne GPS data was post-processed in DGPS mode together with the base station data to provide high accuracy aircraft positions. The GPS trajectory then was combined with the IMU data using loosely coupled approach to yield high accuracy aircraft positions and attitude angles. Then the lidar data was processed using the aircraft trajectory and raw lidar data. After boresighting the lidar data, the ground control points were measured against the lidar data by technicians using TerraScan and proprietary software and the lidar data was adjusted vertically to the ground control. The horizontal datum is NAD83(2011) in meters and the vertical datum is the North American Vertical Datum of 1988 (NAVD88) in meters. The vertical datum was realized through the use of the published/calculated ellipsoidal heights of the base station to process the aircraft trajectory and then later applying the GEOID12B model to the processed LiDAR data to obtain orthometric heights.

Horizontal accuracy of LiDAR data will be achieved by identifying coincident locations between the Intensity rasters and the horizontal checkpoints. Deviations exhibited by the LiDAR Intensity rasters relative to the checkpoints were reported as an RMSE. RMSEr is 0.265 m.

AECOM followed the 2014 ASPRS Accuracy Standards for Digital Geospatial Data to compute the Non-vegetated Vertical Accuracy (NVA) RMSEz and Accuracyz at a 95% confidence interval (RMSEz*1.96) for checkpoints located in non-vegetated open terrain; the required NVA RMSEz is < 10 cm and the required NVA Accuracyz 95% is < 19.6 cm. AECOM utilized the 95th percentile method to determine the Vegetated Vertical Accuracy (VVA) for checkpoints located in vegetated terrain, regardless of vegetation type; the required VVA Accuracyz 95% is < 29.4 cm.

The NVA RMSEz of the DEM was 4.9 cm calculated using 238 independent checkpoints.

The VVA of the DEM at a 95th percentile of the absolute value of vertical errors in all vegetated land cover categories combined using 136 independent checkpoints is 11.64 cm. VVA RMSEz is 5.9 cm.

A complete iteration of processing (GPS/IMU Processing, Raw Lidar Data Processing, and Verification of Coverage and Data Quality) was performed to ensure that the acquired data was complete, uncorrupted, and that the entire project area had been covered without gaps between flight lines. A sensor anomaly caused a few small areas of voids within tile stratmap17-50cm-2996134a1. The Classified Point Cloud data files include all data points collected except the ones from Cross ties and Calibration lines. The points that have been removed or excluded are the points fall outside the project delivery boundary. Points are classified. A visual qualitative assessment was performed to ensure data completeness. The Intensity Image files cover the entire project delivery boundary. A visual qualitative assessment was performed to ensure data completeness. The Intensity Image product is of good quality. The Hydro Breaklines cover the entire project delivery boundary and extend beyond the boundary in a few locations. A visual qualitative assessment was performed to ensure data completeness. No void areas or missing data exist. The Hydro Breakline product is of good quality. The DEM raster files cover the entire project delivery boundary. A visual qualitative assessment was performed to ensure data completeness.

Compliance with the accuracy standard was ensured by the collection of ground control and the establishment of GPS base stations in the project area. The following checks were performed: 1) The lidar data accuracy was validated by performing a full boresight adjustment and then checking it against the ground control prior to generating a digital terrain model (DTM) or other products. 2) Lidar elevation data was validated through an inspection of edge matching and visual inspection for quality (artifact removal). The following software was used for the validation: 1) RiProcess 1.8.3, RiWorld 5.0.2, RiAnalyze 6.2, RiServer 1.99.5) Fugro proprietary software; 20870430.

Data is backed up to tape and to cloud storage.