2017 TNRIS Lidar DEM: Jefferson, Liberty and Chambers, TX (West)

This metadata record describes the bare-earth hydro-flattened Digital Elevation Model (DEM) for the Western Block of the 2017 Texas Coastal LiDAR project. The Western Block AOI covers approximately 289 square miles, including the cities of Liberty, Hankamer, and Anahuac in southeast Texas. This point cloud AOI was collected to meet the density of 8 points per meter. Total area covers equals approximately 1.130 square miles. The DEM has 50 cm horizontal resolution, is in UTM Zone 15 projection, horizontal datum is the North American Datum of 1983 (NAD83 (2011)), vertical datum is North American Vertical Datum of 1988 (NAVD88) using the latest geoid (Geoid12b) for converting ellipsoidal heights to orthometric heights. Units - Meters

Sanborn Map Company was contracted by Texas Water Development Board (TWDB) in cooperation with the Trinity River Authority (TRA) to perform 2017 LiDAR aerial surveys of Texas coastal area of about 1130 square miles. Collections was completed utilizing multi-return systems, Light Detection and Ranging (LiDAR) data in the form of 3-dimensional positions of a dense set of mass points between February 22nd and March 23rd, 2017. ALS70 LiDAR was flown to produce four (4) points and eight (8) points per square meter return density or 0.5 meters and 0.35 meters respectively Nominal Point Spacing (NPS)

Note, The Eastern Block covers approximately 841 square miles, including the cities of Beaumont, Port Arthur, and Nederland in southeast Texas. This point cloud AOI was collected to meet the density of 4 points per meter. It is linked in the 'Related Items' section, below.

To acquire detailed surface elevation data for use in conservation planning, design, research, floodplain mapping, dam safety assessments, and hydrologic modeling. LAS and bare earth DEM data products are suitable for 1 foot contour generation. USGS LiDAR Base Specification 1.2, QL2.

Project Projection, Datums and Units. Projection - UTM Zone 15. Horizontal datum - North American Datum of 1983 (NAD83 (2011)). Vertical datum - North American Vertical Datum of 1988 (NAVD88) using the latest geoid (Geoid12b) for converting ellipsoidal heights to orthometric heights. Units - Meters

USGS Base Specification 1.2

The digital data have been tested and their documentation carefully reviewed. However, the end user and its representatives make no warranty or representation, either expressed or implied, with respect to the digital data and their documentation, their quality, performance, merchantability, or fitness for a particular purpose. The digital data are distributed on "as is" basis, and the user assumes all risk to their quality, the results obtained from their use, and the performance of the data. In no event will the end user or its representatives be liable for any direct, indirect, special, incidental or consequential damages resulting from and defect in the State of Texas or in their documentation. This disclaimer of warranty is exclusive and in lieu of all others, oral or written, express or implied. No agent or employee is authorized to make any modification, extension, or addition to this warranty.

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

Data is available online for bulk or 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.

Microsoft Windows 7; ESRI ArcCatalog 9.3.1.1850

This data set was produced to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 24.1 cm RMSEx / RMSEy Horizontal Accuracy Class which equates to Positional Horizontal Accuracy = +/- 47.2 cm at a 95% confidence level.

Quantitative value: 0.241m

Horizontal error in lidar derived elevation data is largely a function of positional error as derived from the Global Navigation Satellite System (GNSS), attitude (angular orientation) error (as derived from the INS) and flying altitude; and can be estimated based on these parameters.

This data set was tested to meet ASPRS Positional Accuracy Standards for Digital Geospatial Data (2014) for a 10 cm RMSEz Vertical Accuracy Class.

The Western Block AOI actual NVA accuracy was found to be RMSEz = 8.2 cm, equating to +/- 16.1 cm at 95% confidence level. Actual VVA accuracy was found to be +/- 12.5 cm at the 95th percentile.

The overall NVA accuracy for the entire dataset is RMSEz = 9.992.

(The Eastern Block actual NVA accuracy was found to be RMSEz = 10.3 cm, equating to +/- 20.2 cm at 95% confidence level. Actual VVA accuracy was found to be +/- 28.9 cm at the 95th percentile).

LiDAR data is collected for the project area. Post processing of the simultaneously acquired GPS/INS is performed and applied to the laser returns to output a point cloud in the specified project coordinate system and datums. The point cloud data is then subjected to automated classification routines to assign all points in the point cloud to ground, water, overlap and unclassified point classes. Once clean bare earth points are established, all products are created.

LiDAR data is collected within the project area and processed. Control points were used during calibration to verify accuracy.

Data is backed up to tape and to cloud storage.