利用重力场模型解算全球地幔对流应力场

在利用Runcorn模型确定全球地幔对流应力场的研究中,扰动位系数是关键参数之一。在以往研究中,该参数阶次的选取缺乏定量准则,本文引入点质量源法中场源深度与扰动位系数阶次的关系方程,初步对Runcorn模型中截止阶次进行限定。基于该思路,场源深度为30 km的地幔对流应力场应使用2~213阶扰动位系数推算。采用EGM2008地球重力场模型(2~213阶)解算全球地幔对流应力场,并与近8 a内深度大于30 km的M5.5以上地震的震中分布进行比较。结果表明,与板块边界重合的高应力区域和地震震中的分布有较好的对应关系,说明地幔对流可能通过控制板块间汇聚、拉张或错动,进而控制该地区地震的发生。此外,对3处地震发生频数较高的典型区域(欧亚-菲律宾板块边界等)的地幔对流应力及其构造背景进行分析,结果与前人研究结论一致。最后,通过与前人研究结论(2~8阶)进行对比发现,本文解算结果(2~213阶)在太平洋板块西南缘等有较大地震发生的板块边界具更多高地幔对流应力细节,这些地震的发生可能受到小尺度地幔对流的控制。

JPL行星历表的发展及比较

基于DE405、DE421、DE430、DE440星历,计算各大行星在地球质心及太阳系质心惯性系中的位置,比较其他星历相对于DE440星历的行星位置精度。分析讨论各历表下月球的地心位置和速度精度,以及历表对于月球探测器的位置和速度从月心惯性系转为月固系的影响,并给出使用建议。结果表明,各大行星由于受观测数据等因素影响,位置精度差异较大,跨度从m级到106 m量级。对于行星的位置精度,DE421和DE430相对于DE405有1~2个量级的提高,DE430相对于DE421提高50%。DE405历表的月球地心位置、速度精度分别为7 m和0.02 mm/s,DE421历表分别为1.5 m和0.004 mm/s,DE430历表分别为1.3 m和0.0035 mm/s。对于星历用于月球探测器从月惯系转为月固系产生的坐标和速度误差,DE405分别为30 m和3 cm/s,DE421分别为1.3 m和1.2 mm/s,DE430分别为1 m和0.9 mm/s。历表对于月球坐标系转换的影响为m级。对于月球探测器导航及相关任务,推荐使用DE430或DE440行星历表。

Accuracy Analysis for SST Gravity Field Model in China

Taking China as the region for test, the potential of the new satellite gravity technique, satelliteto-satellite tracking for improving the accuracy of regional gravity field model is studied. With WDM94 as referenee, the gravity anomaly residuals of three models, the latest two GRACE global gravity field model （EIGEN_GRACE02S, GGM02S） and EGM96, are computed and compared. The causes for the differences among the residuals of the three models are discussed. The comparison between the residuals shows that in the selected region, EIGEN_GRACE02S or GGM02S is better than EGM96 in lower degree part （less than 110 degree）. Additionally, through the analysis of the model gravity anomaly residuals, it is found that some systematic errors with periodical properties exist in the higher degree part of EIGEN and GGM models, the results can also be taken as references in the validation of the SST gravity data.

Solving Three Types of Satellite Gravity Gradient Boundary Value Problems by Least-Squares

The principle and method for solving three types of satellite gravity gradient boundary value problems by least-squares are discussed in detail. Also, kernel function expressions of the least-squares solution of three geodetic boundary value problems with the observations {Γ zz },{Γ xz , Γ yz} and {Γ xx -Γ yy ,2 Γxy}are presented. From the results of recovering gravity field using simulated gravity gradient tensor data, we can draw a conclusion that satellite gravity gradient integral formulas derived from least-squares are valid and rigorous for recovering the gravity field.

Precise orbit determination for GRACE with zero-difference kinematic method

Thanks to the high performance of the spaceborne GPS receiver and the availability of precise IGS orbit and clock products,zero-difference kinematic precise orbit determination(POD) has been turned out to be a new effective method in orbit determination for the LEO satellites.Zero-difference kinematic POD,which is based on the GPS measurements only from the spaceborne GPS receiver,does not depend on the force models and orbit design.From this point of view,kinematic POD is suitable for the Earth observation satellites at very low altitudes,such as CHAMP,GRACE and GOCE,etc.This paper first reviews the basic zero-difference GPS observation model.Then a modified data quality control scheme is put forward.Finally,a block-wise least squares algorithm,which first separates the parameters into several groups and then solves the parameters by elimination and back-substitution,is discussed and proposed for the kinematic orbit determination.With the above algorithms,we developed kinematic POD software to solve the orbit suitable for one-week GRACE observations.Comparisons with the published Rapid Science Orbit(RSO) indicate that,using our approach to determine the orbit,the accuracy in the radial direction can achieve 3―4 cm for GRACE-A,and 3―5 cm for GRACE-B.

Feasibility study on application of satellite formations for eliminating the influence from aliasing error of ocean tide model

Currently,aliasing error of temporal signal model becomes the main factor constraining the accuracy of temporal gravity field.In provision of three types of satellite formations,i.e.,GRACE-type,Pendulum-type and n-s-Cartwheel-type,which are suitable for gravity mission and composed of observation in different directions,here we design two cases and conduct a simulation experiment on the feasibility to apply satellite formations for eliminating the influence from the aliasing error of ocean tide models.The result of our experiment shows that,when the aliasing error is disregarded,n-s-Cartwheel formation can provide the best conditions for gravity field determination,which,compared with GRACE-type,can improve the accuracy by 43%.When aliasing error of the ocean tide model acts as the main source of error,the satellite formation applied in dynamic method for gravity field inversion cannot eliminate aliasing or improve the accuracy of gravity field.And due to its higher sensitivity to the high-degree variation of gravity field,the Cartwheel-type formation,which includes the radial observation,can result in the gravity field containing more high-frequency signals for the ocean tide model error,and lead to a dramatically larger error.

Numerical Study on the Mixed Model in the GOCE Polar Gap Problem

Gravity gradients acquired by the Gravity field and steady-state Ocean Circulation Explorer(GOCE) do not cover the entire earth because of its sun-synchronous orbit leaving data gaps with a radius of about 6.5° in the polar regions.Previous studies showed that the loss of data in the polar regions deteriorates the accuracy of the low order(or near zonal) coefficients of the earth gravity model,which is the so-called polar gap problem in geodesy.In order to find a stable solution for the earth gravity model from the GOCE gravity gradients,three models,i.e.the Gauss-Markov model,light constraint model and the mixed model,are compared and evaluated numerically with the gravity gradient simulated with the EGM2008.The comparison shows that the Best Linear Uniformly Unbiased Estimation(BLUUE) estimator of the mixed model can solve the polar gap problem as effectively as the light constraint model;furthermore,the mixed model is more rigorous in dealing with the supplementary information and leads to a better accuracy in determining the global geoid.