Mapping Providence Harbor, Rhode Island

The Coastal Institute at the University of Rhode Island’s Graduate School of Oceanography is involved in a program to protect the Narragansett Bay estuary and its watershed. THE CHALLENGE Working with the Rhode Island Coastal Resources Management Council (CRMC), which endeavors to balance economic considerations with environmental protection requirements, there was an interest in acquiring georeferenced LiDAR data for shoreline stability analysis and change-detection studies, and in integrating the LiDAR data (3-dimensional XYZ point positions) of  Providence River’s shoreline with bathymetric (water depth) data.  By integrating these data sets, 3D georeferenced data for above and below the water line would be produced; a considerable technical achievement. Such a solution would be used in ongoing change-detection studies, shoreline stability analysis, beach erosion monitoring, cliff erosion/deformation, etc. throughout Providence harbor. THE SOLUTION: Applanix LANDMark Marine A LiDAR survey team set out to collect 3D images of the beaches, the hurricane barrier and other prominent features along the river’s edge using the new LANDMark Marine system to scan the shoreline area (Figure 1) from a boat. Applanix’ industry-leading combination of POS MV (Position and Orientation System for Marine Vessels), a GNSS-aided inertial navigation system, and POSPac MMS software were used to provide the accurate and robust georeferencing and motion compensation solution, enabling the production of a seamless point cloud from the bathymetric and georeferenced LiDAR data. A GPS base station was deployed to log satellite observables for later post processing. The crew mounted the LANDMark Marine and POS MV equipment on the boat. The GPS base-station observables, together with the raw GNSS  and inertial data logged by POS MV, were then processed using POSPac MMS, Applanix’ unique post mission aided inertial processing package,  producing the Smoothed Best Estimate of Trajectory (SBET). The SBET and the predetermined calibration numbers from the MatchView routine of LANDMark Marine were then used to produce a georeferenced point cloud from the LANDMark Marine scans.  Processing the data took only 15 minutes, enabling the results to be viewed and analyzed while still onboard the vessel. THE RESULT: LANDMark Marine provided a fast, safe and efficient method for obtaining both short and long-range spatial data from a boat’s perspective, and of scanning terrain features beyond the water’s edge. When traveling at speeds of 2.5 to 4 knots, LANDMark Marine generated point clouds of suitable density for use in shoreline change-detection studies.  By operating LiDAR and sonar devices simultaneously, the data sets were referenced using identical navigational data sets derived from the GNSS aided Inertial Navigation System (INS). Only one data gathering mission was required, saving time and reducing the number of personnel deployed in hazardous areas onshore.