以下两篇参考文献的第一作者均为华裔学者程敏康。其一关注的是地球重力场的长期变化，其二是地球重力场低阶球谐系数偶数项的季节变化。 前者使用了 20 年的 Starlette, LAGEOS 1 and 2, Ajisai, Etalon 1 and 2, Stella, and BE-C 卫星的激光观测数据。 后者使用了 1993 到 1996 年的地球动力学卫星 Starlette, Ajisai, Stella, LAGEOS I and LAGEOS II 的 激光观测数据。 美国德克萨斯大学空间研究中心的程敏康曾经与我院进行合作研究，并于去年 9 月就卫星激光测距的重力场应用主题做了学术报告。 参考文献及其摘要： Determination of long-term changes in the Earth's gravity field from satellite laser ranging observations Auteur(s) / Author(s) CHENGM. K. (1) ; SHUMC. K. (1) ; TAPLEYB. D. (1) ; Affiliation(s) du ou des auteurs / Author(s) Affiliation(s) (1) Center for Space Research, University of Texas at Austin, ETATS-UNIS Rsum / Abstract Temporal changes in the Earth's gravity field have been determined by analyzing satellite laser ranging (SLR) observations of eight geodetic satellites using data spanning an interval of over 20 years. The satellites used in the analysis include Starlette, LAGEOS 1 and 2, Ajisai, Etalon 1 and 2, Stella, and BE-C. Geophysical parameters, related to both secular and long-period variations in the Earth's gravity field, including the geopotential zonal rates (J 2 , J 3 , J 4 , J 5 , and J 6 ) and the 18.6-year tide parameter, were estimated. The estimated values for these parameters are J 2 = -2.70.4(10 -11 /yr); J 3 = -1.30.5(10 -11 /yr); J 4 =-1.41.0(10 -11 /yr); J 5 = 2.10.6(10 -11 /yr); J 6 = 0.30.7(10 -11 /yr); C +20 18.6 = 1.56 0.2 (centimeters) and S +20 18.6 = -0.10.2 (centimeters). The amplitude and phase for the 18.6-year tide are in general agreement with the effects predicted by the Earth's mantle anelasticity. The solution accuracy was evaluated by considering the effects of errors in various non-estimated dynamical model parameters and by varying the data span and data sets used in the solution. Estimates for J 3 from individual LAGEOS I and Starlette SLR data sets are in good agreement. The lumped sum values for J 3 and J 5 are very different for LAGEOS I and Starlette. The zonal rate determination is limited to degree 6 with the current SLR data sets. Analysis of the sensitivity of the solution for the zonal rates to the satellite tracking data span suggests that the temporal extension of the current SLR data sets will enhance the solution of zonal rates beyond degree 6. Journal of geophysical research ISSN 0148-0227 1997,vol.102,,pp.22377-22390 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 104, NO. B2, PAGES 26672681, 1999 Seasonal variations in low degree zonal harmonics of the Earth's gravity field from satellite laser ranging observations Minkang Cheng Center for Space Research, University of Texas at Austin Byron D. Tapley Center for Space Research, University of Texas at Austin Abstract Seasonal variations in the Earth's gravity field were determined using satellite laser ranging (SLR) observations from multisatellite. The time series for the variations of the even zonal harmonics, J l ( l = 2, 4, 6, and 8), were determined using the SLR data from the geodetic satellites, including Starlette, Ajisai, Stella, LAGEOS I and LAGEOS II, during the period from October 1993 to December 1996. Owing to uncertainties in the eccentricity excitation for LAGEOS I and II, the variations of J 3 and J 5 were determined using only the SLR data from Starlette, Ajisai, and Stella. The seasonal variations of J 2 , J 4 , J 6 and J 8 become separable using the existing multisatellite SLR data sets collected in 15-day time intervals. The amplitude (normalized and in units of 10 10 ) and phase (in a cosine conversion and in units of degrees) for the annual variation in J l ( l = 2, 3, 4, 5, 6, and 8) are estimated to be (1.25 0.1, 140 10), (2.16 0.21, 341 19), (1.07 0.1, 338 15), (1.12 0.16, 152 16), (0.26 0.17, 337 9), and (1.03 .016, 209 10), respectively. The observed annual variations of J 3 and J 5 are essentially opposite in phase. This phenomenon results in a different lumped sum effect for various satellites. For example, the lumped sum of J 3 and J 5 annual variation from LAGEOS I is twice as large as that from Starlette. The excitation due to the mass redistribution in the atmosphere and ocean and the changes in continental water storage were considered in this study using the available global geophysical data, which included the European Centre for Medium-Rang Weather Forecasts atmospheric surface pressure, the TOPEX/Poseidon altimetry derived sea surface anomalies, and the World Monthly Surface Station Climatic Data. Overall, the variation in the even zonal coefficients due to the atmospheric mass redistribution is responsible for 30% to 60% of the observed annual variations in the node residual for Starlette and LAGEOS I. Comparison indicates that the oceanic mass movement, in particular, the continental water change produce comparable contributions to the seasonal zonal variations. The amplitude of the observed annual variation of J 2 is found to fall between the values predicted from the models of the surface water, ocean, and atmosphere with and without the inverted barometer (IB) oceanic response, but the phase is in good agreement with the IB models. The nontidal mass redistributions in atmosphere, ocean, and continental water change can only account for 13% of the semiannual variation in J 2 but are the primary excitation sources for semiannual variations in the higher-degree zonal terms.
来自ＥＳＡ（欧洲空间局）的消息： ＧＯＣＥ（ Gravity Field and Steady-State Ocean Circulation Explorer ）卫星计划于９月１０日 从俄罗斯的普列谢茨克发射场发射升空。这颗卫星重约 1 吨 , 装备了 6 套灵敏度极高的加速计 , 它们将对地球的重力场进行全面的测量 , 科学家会根据卫星收集的数据绘制一幅高清晰度的地球水准面和重力场。 该卫星的发射因故多次推迟，去年上半年本博客报道过 ＧＯＣＥ发射的预告消息。 以下为 ＥＳＡ网站（ http://www.esa.int/esaMI/GOCE/index.html ）的图 GOCE to map gravity as never before : 该卫星的任务目标(Mission objectives )为: to determine gravity-field anomalies with an accuracy of 1 mGal (where 1 mGal = 10 5 ms 2 ). to determine the geoid with an accuracy of 1-2 cm. to achieve the above at a spatial resolution better than 100 km. 即:以毫伽(10的负5次方乘以米每秒平方)的精度确定重力异常; 以1至2厘米的精度确定大地水准面;空间分辨率100千米。 更多内容可参阅 ： http://www.esa.int/esaLP/ESAYEK1VMOC_LPgoce_0.html
标签: 重力场
