Research And Analysis Of Satellite Gravity Gradiometry Indicator For Exploring The Earth's Gravity Field

The structure of the Earth's gravity field is important geographic information of surveying and mapping.. The determination of the Earth's gravity field in high precision establishes an important foundation for the unification of global height datum and the regional vertical datum of surveying and mapping, which is beneficial to the high-precision applications and services of surveying and mapping. The medium and long wave geoid is absolutely dominant (more than 95%) in the frequency spectrum of the Earth's gravity field. The medium and long wave error of the global gravity field is one of the key problems in the unification of the global height datum and the further improvement of geoid precision. In order to achieve the main scientific objective of physical geodesy in this century which is to determine centimeter-level geoidand develop ultra-high degree model of the Earth's gravity field, the improvement of the accuracy of medium-long wave of the Earth's gravity filed and geoid as well as more massive observations of the gravity filed are necessary.Satellite gravity gradiometry technology with the global, fast, low-cost, high-precision, high-resolution characteristics provides an efficient meansin exploring the medium-short information of the gravity field.The civil satellite gravity gradiometry technology in China is developing for the maintenance of surveying and mapping datum. The engineer complexity, precision and technical level of the gravity gradiometry satellite system are very high. In addition to the need for improvingthe precision of satellite key payloads and the stability of satellite platform, the study of system simulationand design techniques of satellite gravity gradiometry,especially the enhancement of completeness and scientific quantification of the simulation technology are necessary, which is meaningful to clear the research direction in satellite platform and payloads. In the study, the system simulation technology of gravity gradiometry satellite will be done, and the system major technical indicators and payload ones of gravity gradiometry satellite will be designed and analyzed. Besides, multifunctional software system including the functions of numerical simulation, indicator analysis and gravity field recovering will be developed. The main contents and contributions of this paper are listed below:1. The processes of calculation and release of global steady gravity field are overviewed briefly. Then the spectral and precision analysis of representative gravity field models is achieved using GPS/leveling test and other methods. The results show that, the precision of EIGEN-6C3stat model is better than that of EGM2008 in China west region. The contribution of the high-low satellite-to-satellite tracking mode, the low-low satellite-to-satellite tracking mode and the satellite gravity gradiometry mode with the example of CHAMP, GRACE and GOCE satellites to the Earth's gravity field spectrum are concentrated in the long as well medium-long wavelength parts above 600 km, the medium wavelength part above 300 km and the medium-short wavelength part from 200 to 350 km respectively.2.The fundamental theory and methodology of system indicator analysis in satellite gravity gradiometry with analytical and semi-analytical methods are studied, and the design and calculation methods of satellite orbit including terrestrial orbit, orbital inclination, and the requirement of gravity field recovering for orbit are discussed in detail.3. The effects of satellite gravity gradiometry technology on the determination of the medium-short part of the Earth's gravity field, the construction and maintenance of global reference frame, the establishment of precise height datum and the precise orbit determination of satellite are analyzed and discussed in the field of surveying and mapping application.4.Based on the analytical indicator design method, the main technical indicators of the gravity gradiometry satellite including the satellite altitude, POD precision, the precision of payloads are analyzed and derived. Also, the orbit parameters of the satellite is designed and calculated. The results indicate that,For the satellite-to-satellite tracking in high-low mode system, the orbit altitude and the accelerometer precision are the two main factors affecting the resolution and precision of the gravity field. When the orbit altitude is 400km or 500km, the improvement of the accelerometer precision can effectively improve the accuracy of the geoid while the enhance of the geoid spatial resolution is not obvious. While the orbit altitude is lower, the contribution of improvement of the accelerometer to the geoid accuracy is more obvious. For a fixed orbit altitude, the improvement of accelerometer accuracy is proportional to the improvement of geoid accuracy.For the satellite gravity gradiometry system, the orbit altitude and the gradiometer accuracy are the two main factors affecting the resolution and precision of the gravity field. Along with the reduction of orbit altitude, the contribution of the improvement of the vertical component accuracy of the gravity gradiometry to the improvement of geoid accuracy and resolution is more obvious. For a fixed orbit altitude, the improvement of the vertical component accuracy of the gravity gradiometry is proportional to the improvement of geoid accuracy.5. Based on the semi-analytical method on the determination of the gravity field using satellite gravity gradiometrydata, the relationship between the orbit altitude, orbit inclination and other parameters with the gravity field accuracy while that between the accuracy of the gravity gradiome.try and the SST-hl observations with the gravity field accuracy are analyzed using numerical simulation. Also, the control problems of the residual non-conservative forces and the center of satellite mass are discussed. The results show that,In order to reach 1-2cm geoid accuracy with the resolution of 100km, ifthe precision of the precise orbit and the three diagonal components of gravity gradiometry tensor areless than 3cm/(?)and 3mE/(?)respectively, the orbit altitude requires less than 250km. When the orbit altitude is 300km, the accuracy of the three diagonal observations requires better than 1mE/(?.) Taking into account the ability of the orbit control as well as that to the influence of the gravity field determination precision, the initial altitude of the gravity gradiometry satellite should be about 250km and not exceed 300km. The observation accuracy of the SST-hl system should be better than 3cm/(?)while that of SGG system is about 3mE/(?). Due to the influence of polar gaps to the determination of the gravity field, the orbit inclination of the gravity gradiometry satellite should be from 90°to 93°.6. The accuracy of the determination of the gravity field model using semi-analytical method is validated with the numerical simulation method. The results show that, for the circular, strictly repeated, constant sampling and near-polar orbit, the calculation of the semi-analytical method are exactly the same as that of numerical simulation.7. The indicators of a new type of satellite gravity measurement system combining the mode of SST-hl, SST-11 and SGGare analyzed for the first time. The results show that, orbit altitude remains the most key factor influencing the accuracy of the gravity field under the same conditions of observation precision, which is the same as that of the mode combining SST-hl and SGG.If the cumulative geoid error of the highest order of the model are used to evaluate the contribution of the different observations to the combinationcomputation model, the influence of observation of K-band ranging rate and gravity gradiometry is obvious.8. Based on the semi-analytical method and satellite orbit simulation theory on the determination of the gravity field using satellite gravity gradiometry data, a multifunctional software system of satellite gravity gradiometry including orbit simulation, observation simulation, error analysis and other functions, which establishes the platform foundation for the design and analysis of the technology indicators of the gravity gradiometry satellite in China.