Exploring Quantitative Wetlands Mapping Using Airborne Lidar and Electromagnetic Induction on Mustang Island, Texas

Paine, Jeffrey G., White, William A., Gibeaut, James C., Andrews. John R., and Waldinger, Rachel
The University of Texas at Austin, Univ. Stn. Box X, Austin, TX 78737 USA

We combine elevation data acquired using airborne Lidar, conductivity measured using ground-based electromagnetic (EM) induction, and vegetation surveys to examine whether topography and ground conductivity can be used to map coastal wetland vegetation assemblages. In 2003, we acquired elevation data along two transects across Mustang Island, a modern coastal barrier on the central Texas coast. We combined the cm-scale elevations with conductivity measurements and vegetation surveys acquired at 20-m spacings from the gulf beach to the bay shore. Wetland vegetation responds to both elevation and salinity; because ground conductivity is strongly influenced by soil salinity, we used EM induction measurements as a salinity proxy. Elevation and conductivity information, acquired either on the ground or from aircraft, represent a quantitative complement to traditional wetland mapping methods that rely upon aerial photographs.

Along both transects, conductivities were negatively correlated with elevations. Highest average conductivities (1565 to 1745 mS/m) were measured on wind-tidal flats (elevation -0.05 to 0.5 m NAVD). Salt marshes at elevations of -0.1 to 0.3 m (low) and 0.2 to 0.8 m (high) had lower average conductivities of 1270 to 1365 mS/m (low marsh) and 805 to 868 mS/m (high marsh). We measured relatively low average conductivities of 92 to 223 mS/m in low and high fresh marshes at elevations of 0.5 to 3.1 m. Dunes and vegetated barrier flats with elevations as high as 7.5 m NAVD had the lowest conductivities of 12 to 96 mS/m. Combined or alone, elevation and conductivity data allow better discrimination among coastal wetland environments than can be achieved from aerial photographic interpretation.