Abstract:

This dataset contains a seamless high resolution, two-meter, topographic lidar digital elevation model (DEM) of the Upper Texas Coast. The elevations in this DEM represent the topographic bare-earth surface. The dataset is a fusion of several airborne topographic light detection and ranging (lidar) surveys acquired by various surveyors between the years 2015 – 2019. The landward extent of the lidar surveys selected for the creation of this DEM is determined by the boundary of the ADvanced CIRCulation (ADCIRC) TX2008_R35H computational mesh obtained from the Computational Hydraulics Group at The University of Texas at Austin. The spatial reference used for the tiles in the DEM is in Universal Transverse Mercator (UTM) Zone 15 in units of meters and in conformance with the North American Datum of 1983 (NAD83). All bare earth elevations are referenced to the North American Datum of 1988 (NAVD88). The 2-meter DEM of the lower Texas coast is available under GRIIDC Unique Dataset Identifier (UDI): HI.x833.000:0010 (DOI: 10.7266/Z7WG9EGN).

Suggested Citation:

Su, Lihong, Mukesh Subedee, Marissa Dotson, James Gibeaut, Brach Lupher, Anthony Reisinger, and Rhiannon Bezore. 2021. 2-meter Topographic Lidar Digital Elevation Model (DEM) of the Upper Texas Coast. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/2MYPTJ7Y

Purpose:

High-resolution topographic data is valuable in geoscience studies and mapping applications. Over the decades, the state of Texas has collected publicly available lidar data, with the extent of each survey varying from county-wide surveys to beach and bay shoreline surveys. Before the creation of this DEM, a fusion of the available lidar along the Texas coast into one seamless coast-wide DEM had yet to exist. This dataset was developed within the Harte Research Institute for Gulf of Mexico Studies (HRI) for the purpose of sea level rise and hydrodynamic storm surge modeling along the entire Texas coast for the Texas Coastal Resiliency Master Plan (TCRMP).

Data Parameters and Units:

Elevations are in meters relative to the NAVD88 datum, geoid2012b. The spatial reference used for the tiles in the DEM are in NAD83, UTM Zone 15.

Methods:

The las files were first checked if they fall in the boundary of the ADCIRC mesh for modeling. A las tile is inside the boundary if any one of its four corners falls within the ADCIRC mesh boundary. All necessary las file’s horizontal coordinates were converted to UTM 15 and vertical coordinates to NAVD88. Furthermore, any files that use geoid1999, geoid2003, or other geoids were converted to geoid2012b. The las files were then gridded by inverse distance weighting (IDW) with the three nearest points in order to produce 2 m cell raster files. If no lidar points are within the search range of 3 m, the two-meter cell is assigned no data. Five parameters were computed for each 2 m cell: point density, average elevation, minimal elevation, maximum elevation, and elevation variance. Only ground points within a 2 m cell are included. A lidar survey usually has 10 to 2000 files. After gridding lidar points in a las file into a GeoTIFF file, we get 10 to 2000 raster tiles. We mosaicked these tiles into larger images in order to fuse multiple surveys. The code to fuse surveys first collects the geographic range of all tiles. It also gathers the extent of each lidar survey. If the range is larger than 15,000 x 15,000 pixels of 2 m, the range will be divided into two to ten or more sub-ranges, so that each sub-range is smaller than 15,000 pixels. After obtaining the geographic extent of each sub-range, all tiles were mosaicked into a sub-range if left-upper corner of a tile was in the geographic extent of a sub-range. To fill in the no data holes that exist in new mosaicked images, we used a morphology closing operation to close all areas that are less than 41 x 41 pixels (81 m x 81 m). Buffers were generated 50 pixels from the boundary of any no data areas. The no data cells next to valid elevation data were assigned a value of 1, the no data cells next to value 1 cells were assigned a value of 2, and so on. The computed elevation for a buffer cell is the average elevation of its 3x3 neighboring cells. First value 1 cells were computed, then value 2, and so on until 30 buffer cells at max for all no data areas that are closed using the morphology closing operation. Therefore, all holes in data less than 41 x 41 pixels were filled. To make a smooth surface along the edges of lidar surveys, we first generated buffers of 10 pixels (20m) within valid regions along all edges of no data cells and along the boundary of a mosaicked image. The buffer is on valid data regions. For example, for a hole of no data, the buffer is 10 circles around the hole. The first circle comprises cells on the edge of the hole. The cells on edges were assigned 1. The second circle was next to first circle, and its cells are assigned 2, and so on until tenth circle. All other data cells beyond the 10th were assigned 10. Where multiple surveys were available, the weighted average method wa used to compute the elevation for a cell. Here 1 means 1/10 weight for the survey, 9 means 9/10 weight, 10 means 1.0 weight. This ensured a smooth surface was produced along the edges where two surveys overlap. One of the surveys used in the fusion was considered inferior to other newer lidar surveys due to lower quality. To resolve this issue, the inferior dataset was excluded in the fusion if a newer dataset was available. Once these raster tiles are generated, they are mosaicked together for the upper Texas coast within UTM 15 zone.

Provenance and Historical References:

The following Lidar data were used to obtain this dataset: 1. 201901_MatagordaBay_LIDAR [“Texas Matagorda Bay 2019 Lidar”, published 2019-09-17, originator United States Geological Survey (USGS) ]: https://data.tnris.org/collection/8774ed51-b633-4f03-85ca-94c311ee0a88 2. 201801_UpperTXCoast_LIDAR [“Texas Coastal Lidar Mapping Project”, published 2018-04-08, originator Texas Water Development Board (TWDB)]: https://data.tnris.org/collection/b5bd2b96-8ba5-4dc6-ba88-d88133eb6643 3. 201702_JeffersonChambersLibertyCounty_LIDAR[“Texas Coastal Lidar Mapping Project”, published 2017-04-20, originator TWDB]: https://data.tnris.org/collection/12342f12-2d74-44c4-9f00-a5c12ac2659c 4. 201603_NechesRiverBasin_LIDAR [“Texas Neches Lidar Project”, published 2017-11-21, originator USGS]: https://data.tnris.org/collection/67af6a3e-2c73-446d-a5b7-243b4b6ae4ec 5. 201502_Matagorda_LIDAR [“2015 Matagorda Bay Topographic Lidar All Points Data (UTM zone 15, published 2016-11-09, originator Bureau of Economic Geology (BEG)]: Data was obtained on hard drive from the Bureau of Economic Geology (BEG) at the University of Texas at Austin 6. ADCIRC_Mesh_Boundary - TX2008_R35H computational mesh boundary obtained from U.S. Army Corps of Engineers (USACE), 2011. Flood Insurance Study, Coastal Counties, Texas. Intermediate Submission 2: Offshore Water Levels and Waves.

Individual Files: