Beach and Dune Analysis Using Chiroptera Imaging System, South Padre and Brazos Islands, Texas Gulf Coast

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2014

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In early 2013, the Bureau of Economic Geology (BEG) acquired lidar data and color infrared (CIR) aerial imagery of South Padre Island and Brazos Island, Texas (Mansfield Channel to Rio Grande), to:

  1. Evaluate the position of the shoreline, vegetation line, and back dune line.
  2. Map geomorphic units.
  3. Extract maximum dune crest elevations.
  4. Calculate rates of long-term shoreline change.
  5. Provide beach-dune system volume analysis.

Data were collected using the BEG's Chiroptera airborne system, which collects topographic lidar data, shallow bathymetric lidar data, and natural color/color infrared imagery. Topographic data and CIR images were collected for a 500-m swath (three passes) of South Padre Island landward of the shoreline. Bathymetric data were collected from the shoreline 1000 m seaward. The bathymetric data-collection portion of this project was intended to establish the depth penetration and water-clarity limitations of Chiroptera on the open Gulf of Mexico coast.

The lidar data and CIR imagery can be used for numerous scientific and coastal-monitoring purposes, including mapping of geomorphic units, quantifying shoreline change, and analyzing beach and dune system volumes.

Geomorphic units along South Padre Island, mapped by combining CIR aerial imagery and topographic lidar data, consist of wetland and upland habitats. Wetland habitats are interpreted from BEG-captured 2013 CIR aerial imagery and follow the National Wetlands Inventory (NWI) classification. Upland geomorphic units are mapped from CIR imagery draped on lidar digital elevation models to aid geomorphologic mapping. Upland units include washover channel and fan, fore-island dune complex, fore-island dune ridge, vegetated barrier flat, mid-island dune complex, and back-island dune complex.

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