Multibeam Data Evaluation for DOLPHIN and Ship Collection Platforms

This report presents an evaluation of the performance of the Deep Ocean Logging Platform with Hydrographic Instrumentation and Navigation (DOLPHIN) Remotely Operated Vehicle (ROV) as a platform for collection of multibeam sonar data to produce bathymetry. Three data sets were collected during the scheduled survey tests and are available for evaluation and comparison. The three surveys were conducted in the Norfolk Canyon off the mouth of Chesapeake Bay in Virginia. The DOLPHIN, equipped with an EM 1000 echo sounder with EM 100 electronics, and the National Oceanic and Atmospheric Administration's ship Whiting, carrying a Hydrochart II (HC II) sonar, surveyed from 5 to 7 August 1992, with the Whiting acting as the DOLPHIN's mother ship and following the DOLPHIN a few hundred meters behind. The USNS Littlehales conducted its survey of the same area from 23 to 25 August 1992, with a hull- mounted EM 100 echo sounder. The quality of the multibeam data collected by DOLPHIN is evaluated in terms of the root-mean-square (rms) noise in each beam, the frequency of dropouts suffered, and the presence of spurious noise, and is compared to data from the Littlehales EM 100 and the Whiting/HC II. The frequency, amplitude and distribution of heave, roll, and pitch of the DOLPHIN/ EM 100 are investigated, and when possible, compared to the corresponding data from the Whiting. Results indicate the DOLPHIN is a stable survey platform for multibeam data, which introduces negligible noise to the system and has very infrequent dropouts. Gridded bathymetry from the three platforms are compared and show good agreement. The largest rms difference was between the DOLPHIN and the Littlehales. Repeatability tests yield a consistent bathymetry for the DOLPHIN.