Generating Point Clouds of Drifting Iceberg Sails with Helicopter-borne Photogrammetry: Trials from Offshore Newfoundland, April 2015

Abstract:

Accurate characterization and volume determination of iceberg sails is important for calculating wind drag effects on iceberg drift and estimating total iceberg mass, respectively. This information is of direct relevance to the shipping and offshore hydrocarbon industries operating on Canada’s east coast. A field campaign was completed in April 2015 offshore Newfoundland and Labrador, Canada to assess the precision of point clouds generated from successive helicopter-borne aerial surveys of two drifting iceberg sails. A minimum of three GPS tracking beacons or survey-grade GPS units were deployed per iceberg and were paired with ground control points (GCPs). Two to eight flight lines were conducted per survey of the large (0.12 km²) and small (0.02 km²) icebergs, with altitudes varying from 750 to 1000 m. The nadir images were captured via a wireless connection to the DSLR camera which was contained within a ‘pod’ externally mounted on an MBB Bo105 helicopter. Drift was primarily translational over the survey periods, with average drift speeds of 0.59 and 0.95 km hr^-1 and total drift magnitudes of 194 and 272 m for the large and small icebergs, respectively. Iceberg volumes varied by 15 to 17% between surveys as initially calculated in AgiSoft Photoscan after manual point cloud cleaning. Additional results of a cloud-to-cloud differencing algorithm, after drift correction with the georeferenced GCPs, suggest that repeat photogrammetric surveying is an effective method for identifying local iceberg deterioration on the order of > 0.8 m. This method of iceberg aerial survey was determined to be effective but challenges included helicopter use in a remote offshore location, GCP deployment on a moving and possibly unstable target and difficulty in acquiring adequate coverage of vertical sidewalls with a nadir camera angle.