St. Petersburg Coastal and Marine Science Center
Navigation and Data Acquisition
To improve data collection, accurate mapping, and real-time information, ship-board operations use a combination of Differential Global Positioning System (DGPS), real-time kinematic (RTK) surveys, a pitch, roll, and heave sensor, and onboard computing systems. Differential corrections are broadcast by the U.S. Coast Guard and NAAS satellites and can increase accuracy from 100 meters to 10 meters. For nearshore RTK surveys, data from a reference unit, operating at a surveyed location, can be applied to the mobile shipboard receiver to reduce errors and improve vertical accuracy to .02 meters. The roll, pitch, and heave of the vessel is detected with a digital sensor and integrated with the high-precision GPS data to adjust for the vertical motion of the vessel. Onboard computers integrate information from each component to produce accurate, real-time positioning of the ship and of incoming data from scientific sensors. Precise location is important for accurate location of acquired data and subsequent feature mapping.
USGS navigation systems use a digital DGPS Max CSI navigation receiver with HYPACK software, CODA Octopus F190 Omnistar/WAAS corrected DGPS/IMU, Ashtech RTK receivers and other GPS WAAS/DGPS receivers.
Recently incorporated onboard the R/V G.K. Gilbert is a Coda Octopus F-190, dual-GPS antennae for heave, pitch and roll compensation to correct for vessel motion in the ocean. The dual-antenna unit uses precise, dual-frequency GPS signals to measure antenna displacements on the boat to <6 centimeters. The antennae are exactly one meter apart. The correction is good enough for seismic surveys, but RTK is still used for bathymetric surveys.
Here are two informational sites about GPS: