A Study On Heterogeneous Marine Gravity Data Combination Technology

Research on combining heterogeneous gravity data to construct high accuracy marine gravity map is a key techqiue of gravity aided navigation system, marine gravity map is the basic of gravity aided navigation system. Whether the local characters of gravity field is obvious and whether the accuracy and resolution of gravity data meet the demand directly decides if the gravity navigation method works well. There are three kinds of gravity data: satellite altimetry data, airborne gravity data and shipboren gravity data, but they have their own advantadges and applying area, describe different frequency gravity information. Combination heterogeneous gravity data can make up the only measurement area limitation, however, which arise the problems in how to combine the gravity data from different measurent manners. In this paper, how to combine satellite altimetry data, airborne and shipborne gravity data is studed.The geopotential characteristics and the definition of disturb vectors are summaried, meanwhile, the survey principles and computation method of three marine gravity measurement manner are introduced. That is, the principle of satellite measurement and the method of using satellite altimetry derive marine gravity anamoly, basic rule of airborne gravity measurement system and the downward continuation technique, ship-borne measurement characteristics and its computation method. These are the preconduction of the research on the herogeneous marine gravity combination.The remove-restore technique is analysised in detail. Based on the general formula, the two basic principles Meissl scheme and Helmert condensation scheme are studied. They are used to compute the geopotential model attribution and the terrain directive and indirective influence. The application of remove-restore technique to the satellite altimetry derived gravity and downward continuation of airborne gravity is researched. By the example of airborne gravity, the performence of remove-restore is demonstrated. To analysis the influence of height and terrain to the downward continuation, the effective method is presented to resolve the influence. And its adaptive ability to the noise data is also studied.For the marine gravity field is a special application, the relationship between depth and gravity is studied. The ideal that using ship-borne gravity data and the pri-depth information to estimatie local depth model by least squares collocation (LSC) is presented. Set the covariance computed by gravity data to be the experience covariance to approach the covariance used in the LSC, and to compute the corresponding covariance matrix for estimating depth model. The RTM correction of the estimated model is applied to the remove-restore technique to substitute the Helmert method. In the paper, a lots of experiments is performed to value the estimated depth model and the performance of its RTM correction in the remore-restore technique.The combination method to combine satellite altimetry and airborne gravity and shipborne gravity is researched. With the spherical harmonics analysis, based on the idea that using residue gravity data to compute the spherical harmonic corrected coefficients and add to the original coefficients, an iteration method is presented to correct the local gravity model. The performance of this method is demonstrated by the simulations.The effect of gravity data grid distance and depth RTM correction to the combination results is studied, meanwhile, the combination gravity map is applied into gravity navigation system. In the experiment area, the navigation result is contrasted to the registration result on the shipborne gravity map. According to the results, even the local gravity data has large grid distance, using the combination methods also can achieve better registioan result.