Results from the first Topo-Bathymetric lidar surveys of the Chiroptera II sensor: Improved geological mapping and coastal hydrodynamic models

English Abstract:

The Applied Geomatics Research Group (AGRG) within the Nova Scotia Community College (NSCC) acquired a new shallow water airborne topo-bathymetric lidar sensor and flew the first missions in September 2014. The survey areas consisted of several embayments along the Northumberland Strait. The low flow rates associated with the inner bays promote high volumes of sediment cover and bedrock features are rarely exposed. These sediments can be re-suspended in the water column during periods of increased wave activity, thus increasing turbidity and limiting the laser penetration depth. The reflectance of the seabed also effects the laser also effects the maximum depth achieved. The area near Cape John, Nova Scotia where Carboniferous sandstone rocks are exposed provides insights into how the sensor can enhance and extend structural information on geological maps. Traditional topographic lidar reveals a smooth terrestrial landscape with limited outcrop as a result of the deposition of glacial till. The bedrock is exposed along cliffs at the coast where limited bedding and structural measurements can be taken. The first attempt to survey was aborted on Sept. 25 because of high water turbidity levels and poor bathymetric lidar returns. However, after a day of reduced winds it was surveyed on Sept. 26 with penetration to 6 m water depth. The results revealed several previously uncharted features on the seabed including reefs. Other than near-shore sand bars, the offshore currents have scoured the seabed to expose the bedrock revealing bedding planes and fault structures. Details of the strike of the beds offshore reveal new details on the folding and faulting in this area and these new data can be used to update the existing geological map, NSDNR Map ME 1990-014. The circulation of water within sheltered bays is important for aquaculture site selection. The results of a hydrodynamic model using Mike-21 for Little Harbour, NS were compared between input data consisting of the original chart information based on a sparse distribution of soundings and the new lidar derived DEM. The results indicate the improved input elevation data produces a more refined and detailed set of outputs. The model results have not been validated against in-situ water levels or current measurements yet, although that is planned this field season.