Research For Gravity Gradient Aided Inertial Navigation System

Currently, inertial navigation system (INS) is acted as one of the navigation tools by a variety of carriers. But the INS's position error grows larger and larger as time goes on. In order to suppress the accumulation of error, most of carriers use external aided navigation system such as satellite-aided navigation system, terrain-aided navigation system to amend the INS's position error. Each method is easily disturbed by outside interferences for that all of they either need to transmit signals or receive signals. This paper presents a fully independent aided navigation system-gravity gradient aided navigation system (GGI/INS).The key technologies for gravity gradient aided navigation system are inertial navigation system, gravity gradient map, gravity gradiometer and gravity gradient aided navigation algorithm. A detail analysis is made for these technologies. The main contents are as follows.(1) Inertial navigation system is the basis of the gravity gradient aided navigation system. So the paper mades the strapdown inertial navigation system as the object, discussing common coordinate system of inertial navigation system and their mutual relations, establishing navigation equations and error equations for the strapdown inertial navigation system. These are the premise for the gravity gradient aided navigation system.(2) There is no global gravity gradient database for various reasons now. Therefore, it is an urgent problem to simulate gravity gradient map making use of the existing conditions. The paper uses the spherical harmonic model to simulate the earth's low frequency, long wave gravity gradient component and uses terrain data to simulate the earth's high frequency, short wave gravity gradient component. The characteristics of earth's gravity gradient is analysed using the result. The relationship between the calculated gravity gradient and the terrain height is analysed. Finally, gravity gradient map simulation method is given.(3) Gravity gradiometer (GGI) is another key technology for gravity gradient aided navigation system. The principle of accelerometer-based gravity gradiometer is derived. The full tensor gravity gradient measurements are derived using the United States Bell/Aero gravity gradiometer. A 12-accelerometers gravity gradiometer is designed basing on the principle. The linearized error equations are derived when the gravity gradiometer is installated on the INS system as strapdown or platform mode. These results will be used in navigation filter algorithm.(4) Filtering algorithm is the last key technology for gravity gradient aided navigation system. The external kalman filter algorithm is analysed. Dynamic systems linearized process and operation process of kalman filter are derived. The gravity gradient aided navigation system algorithm is established. The improvement for inertial navigation system is anylased using gravity gradiometer. The impacts of inertial measurement device, gravity gradient, gravity gradiometer noise, gravity gradiometer type and other factors for navigation system are analysed.(5) The gravity gradient aided navigation system is affected by the flight speed, altitude, gravity gradient and other factors. The system sensitivity is different under different conditions. The paper analyses the sensitivities of gravity gradient aided navigation system for various conditions, giving limitations for the design of gravity gradient aided navigation system.