Research On Key Technology Of Shipboard Laser Interferometric Absolute Gravity Measurement

The ocean occupies more than 70%of the Earth’s surface,and marine gravity measurements are essential to geoscience research,undersea resource surveys,inertial navigation,and geodesy.Because it does not have solid rocks on land,the ocean can only be measured by using satellites or measuring gravity on mobile platforms such as aircraft and ships.In contrast,shipborne gravity measurements can obtain the Earth’s gravity field with higher spatial resolution and precision.Until now,shipborne gravity surveys are relative gravity measurements,and these relative gravimeters need to be calibrated before and after the measurement operation to eliminate zero drift error.The gravity measurement environment in the vicinity of the marina gravity base point changes significantly and can bring calibration errors.In the distant sea(such as the Pacific Ocean and Indian Ocean waters),long periods and multiple voyage segments do not pass the gravity base point.Only two base point comparison before and after the return voyage causes significant errors.In addition,if the vessel stops at an offshore terminal in the middle of the voyage or takes shelter from the wind at a specific place,there may be no gravity base point.Absolute gravity measurement directly measures gravitational acceleration,which can provide a new method and technology for marine gravity measurement.Absolute gravity measurement technology can overcome the zero drift,calibration,error accumulation of the relative gravity measurement,and other problems with high efficiency,economy,and no need to remeasure the characteristics.At the same time,the absolute gravity measurement results can also provide a calibration basis for the fusion of multi-source gravity measurement data from different sensors and reference bases.The unique advantages of shipboard absolute gravity measurement make it one of the critical development directions for future marine gravity survey technology.At present,absolute gravimeters can only work in static conditions.The absolute gravity measurement on sea surface shipboard is still in the exploration,and experimental stage,especially the shipboard absolute measurement based on the laser interference absolute gravity measurement principle in China,which is almost in the research gap.In this paper,the critical technology of shipboard absolute gravity measurement based on the laser interference principle is studied,and the following results are achieved.(1)The dynamic conditions of the laser interference absolute gravity measurement system are studied for the first time.The preconditions for carrying out shipboard laser interference absolute gravity measurement are clarified.(2)The effects,correction methods,and precision of shipboard dynamic disturbance factors(vertical,pitch and roll,and horizontal motion)are comprehensively analyzed for the first time.Especially the dynamic constraints of the signal processing algorithm based on the background vibration parameters are proposed.(3)The linear vibration separation method is expanded in shipboard absolute gravity vertical vibration suppression to suppress vertical vibration interference and improve measurement accuracy.(4)The first international advanced shipboard absolute gravity measurement system with laser interference principle was constructed,and the first domestic test on wave simulator platform was completed.The prototype system was initially demonstrated to have an accuracy better than 5mGal and a precision of 1.3mGal,which meets the requirements of absolute gravity survey in the ocean.