Tightly Integrated Inertially-Aided Post Processed Virtual Reference Station Technique for Marine Hydrography

Today’s primary positioning technique for near-shore, multibeam for Marine Hydrography involves integrating GPS and inertial navigation systems (INS). The Inertial Measurement Unit (IMU) aids in reducing GPS noise as well as providing high bandwidth, un-interrupted solutions during GPS outages. For high precision surveys (5 cm or better in X, Y and Z), the most common technique has been the post processed Inertially-Aided Kinematic Ambiguity Resolution (IAKAR) mechanization, which requires a reference station in the proximity of the survey area. The reference station helps to mitigate atmospheric and satellite biases and to resolve integer ambiguities. In these cases the GPS rover position is required to be within 20 km of the reference station. Otherwise the atmospheric biases degrade the accuracy of the results, imposing significant limitations and increased survey costs. This paper describes the Post Processed Virtual Reference Station (PPVRS) technique, which makes use of GPS network stations to determine atmospheric biases at the rover positions and which tightly integrates GPS with inertial data to provide a continuous, high-precision navigation solution with baselines of up to 100 km. A standard NOAA hydrographic survey was chosen in the Chesapeake Bay to test the PPVRS work flow. Data acquisition was conducted aboard NOAA Ship RUDE (pronounced Rudy) on October 18 th 2007 as part of the acquisition of a multibeam reference surface. At 90 feet in length, 22 feet breadth, and 220 tons displacement, RUDE has a cruising speed of 10 knots and a range of 1,000 nautical miles. RUDE performs inshore hydrographic surveys along the east coast in support of NOAA's nautical charting mission and is equipped with some of the most technically advanced hydrographic and navigation equipment available. A Beta version of POSPac Version 5.0 was used to process the POS M/V Data and produce a Smoothed Best Estimate of Trajectory (SBET) file for import into Caris HIPS and SIPS, NOAA’s Hydrographic Processing software. The result is a positioning method for hydrographic surveying with the necessary precision for eliminating the need for dedicated GPS reference stations for all of the continental U.S. inland waters and near shore areas. PPVRS changes the way hydrographic surveys are acquired by reducing logistics and ensuring sub 5 centimeter positioning.