NOAA Charting - Tongass Narrows Ketchikan, Alaska

Reson 8101 and 8124 multibeam sonar systems were used to locate and determine the least depth over the obstructions, wrecks and shoals, as well as determining the least depths over the entire project area. A limited shoreline and near shoreline feature verification survey was conducted. The shoreline survey verified the general location of the Mean High Water (MHW) shoreline, the Mean Lowest Low Water (MLLW) line and all features seaward of MLLW.

A 44' leased vessel was used for the majority of the work and the remaining data was collected from one of our 24' vessels. Positioning was achieved with a Seatex Seapath 200 and Trimble 7400. Sound velocity data was collected with Applied Microsystems velocimeters, models 3317, 3279, and 4425. Vessel attitude was determined using the Seatex Seapath 200 and a SG Brown Meridian Gyro.

Our hydrographers calibrated equipment; determined the static transducer draft and settlement of the vessel were measured and remained properly accounted for throughout the survey; conducted accuracy testing; accounted for sensor alignment and biases; and determined, processed and applied necessary data corrections to the deliverables.

We developed Maplets to verify the Shoreline RSD and included them on Smooth Sheets.

Task Orders for Tongass Narrows required:

• Mobilizing, demobilizing, and moving between survey areas;
• Performing all surveying;
• Establishing geodetic control;
• Positioning floating aids to navigation;
• Installing and maintaining required tide gauges;
• Processing data;
• Preparing reports, plots, and other deliverables; and
• Determining the least depth on wrecks and obstructions from the data acquired during the task order.

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