Marine Gravity Aided Navigation Methods With Their Applications

The marine gravity aided navigation is defined as the technique which improves the precision or corrects the drifted biases of INS by the marine gravity information. And the marine gravity aided navigation methods include the gravity compensation for INS, the gravity map-matching navigation and SLAM.The marine gravity aided navigation systems are composed of the inertial navigation systems, the real-time marine gravimetry systems, the marine gravity reference maps and the algorithms for aiding navigation. In the paper, the whole systems of marine gravity aided navigation are the research objects, and the marine gravity aided navigation methods are proposed completely and their technical feasibilities are demonstrated. Firstly, the INS error properties with their correction are analyzed. Secondly, the fundamental principles of the marine gravity aided navigation are presented, which includes improving the INS precision by the gravity compensation and bounding the INS drifted errors by the gravity matching navigation with the gravity reference map or by SLAM without the gravity reference map. Thirdly, the technical characterizations and the survey approaches of the marine gravimeters and the gravity gradiometers are discussed. Fourthly, the methods for the marine gravity reference mapping by the modern marine gravity exploration technologies such as the altimetry are studied, which includes the crossover adjustments, the collinear adjustments, predictions of the vertical deflections and the marine gravity maps from the altimetry data. Fifthly, the gravity compensation methods for INS are proposed, which can be classified into two categories according to the determination of the gravity vectors. One is the gravity compensation based on the gravity reference map and another based on gravity gradiometers observations. Sixthly, the integrated gravity map-matching navigation methods are proposed according to the gravity field's properties, which include the procedures of the integrated gravity map-matching navigation, the influences on the gravity map-matching navigation precision from the errors of the INS, the gravity reference maps, the real-time gravimetry systems, and the approaches of evaluating the gravity field map-matching applicability were proposed. Seventhly, the SLAM is explored to bound the INS drifted error where there is no gravity reference maps. Eighthly, the simulations of the gravity aided navigation were implemented in the 10 o S ~10oN?16 0oE~180oE sea area, which includes the simulation of the gravity compensation for INS based on the gravity reference map or based on the gravity gradiometers observations and the simulation of the gravity matching navigation based on the gravimeters observations or the gravity gradiometers observations. In the end, the applications of the marine gravity aided navigation systems were designed according to their status and requirements.In the paper, the conclusions and the innovations are as follows. (1)The marine gravity aided navigation is able to determine the navigation velocities and positions related to the earth referenced coordinate systems directly and their navigation precisions don't be influenced as the navigation time or distance is added. It doesn't need to float on the sea surface, or receive outside position information or communication message from the earth. And it can be used to correct the underwater INS errors and resolved the underwater covert navigation problems completely. (2) The gravity gradiometers are the ideal real-time marine gravimetry systems. And the lagged time and the E?tv?s effects must be taken into account if the gravimeters are used as the real-time marine gravimetry systems. (3)The fast computing algorithms for the altimetry crossovers and the nominal points with their mean sea surface heights precisely are presented, which refined the altimetry crossover adjustments and the collinear adjustments. And it is proved that the marine gravity reference map resolution is superior to 2?×2?and their precision is superior to 7 mGal nowadays, which make it possible for the realization of the marine gravity aided navigation. (4) The rigorous formulae for the influences on the INS from the INS gravity parameter errors are induced, which proves that the horizontal navigation errors from the INS gravity parameter errors can reach hundreds of meters in one hour. And the INS gravity parameters'errors have become the main error causes of the high precise INS. (5)In the experiment sea area, the gravity compensation based on the gravity reference map improved the INS precision by 16000 meters in 100 hours and the gravity compensation for the INS based on the gravity gradiometers improved the INS precision inefficiently, and the gravity map-matching navigation based on the gravimeters bounds the INS errors less than 3000 meters and the gravity map-matching navigation based on the gravity gradiometers bounds the INS errors about 2000 meters.