Vessel Dimension Control & System Calibrations
Utilising direct measurements from Total Station, Laser Scanning and Photogrammetry methods, GEOSIGHT are specialists in the capture of precise and accurate dimension control data for hydrographic survey and construction support vessels. GEOSIGHT surveyors in consultation with the client can define an accurate vessel reference frame and subsequently accurately define this relationship to survey sensor reference frames such as motion reference units, survey heading systems (gyros and GNSS antenna), USBL positioning systems and multibeam echosounders. The dimension control will also accurately define sensor offsets relative to the chosen central reference point.
Permanent and recoverable control points will be established on the vessel and coordinated to the vessel reference frame to within a tolerance ±0.01m relative (at the 95% confidence level) in X, Y and Z. All relevant components of the positioning system, motion reference units and bathymetry sensors are established within the vessel reference frame within a tolerance of ±0.02m relative (at the 95% confidence level) in X, Y and Z. Where appropriate, the rotations of each sensor around the X, Y and Z axis are determined by the dimensional control survey to within ±0.5 degrees (at the 95% confidence level).
Upon completion of the dimension control survey, GEOSIGHT specialist survey vessel dimension control surveyors will prepare and issue preliminary results to enable survey vessel verifications and calibrations to commence without delay. Full dimension control survey reporting will follow within an agreed timeframe and will consist of a professional survey report designed to remain with the vessel as a clear and concise permanent record of the methodology and results of the vessel dimension control survey procedure carried out.
The Dimension Control Survey is a vital component of all hydrographic survey projects and for any vessel engaged in offshore positioning to help clients improve their data accuracy and to build and minimise their survey error budgets.
Survey Vessel Calibration and Verification Surveys
Static GNSS Verification
GEOSIGHT surveyors can perform Static Positioning Checks on installed GNSS antenna to monitor the three-dimensional position of either the primary GNSS antenna or another appropriate point within the vessel reference frame. We will install local survey control within the required horizontal datum, typically using NRTK solutions such as SmartNet within the United Kingdom. From our installed shore control we can extend the horizontal and vertical position to the vessel for direct comparison with the vessel GNSS position. Our report will state the computed statistical reliability of both the horizontal position and the height measured.
GYRO Calibration and Verification
When a gyro is installed on a vessel, it is imperative that a gyro calibration is performed to accurately determine the misalignment angle between the gyro’s north and the local north of the coordinate system of the vessel.
Once you have accurately determined this precise relationship, it is possible to accurately transfer the horizontal element of your vessel local reference frame into a global reference frame, allowing your entire survey system to benefit from the accuracy of the gyro.
GEOSIGHT Surveyors are specialists in the conduct of alongside gyro calibrations to accurately determine the gyro C-O value. We use the latest high accuracy NRTK GNSS systems to determine quayside baselines and the highest accuracy Leica total stations to extend this baseline onto the local north baseline of the coordinate system of the vessel.