The combination of satellite gravimetry measurements with other techniques can promote the integration of the "Three Pillars" of geodesy, namely, the Earth's shape, gravity field, and rotation. Combined processing of Gravity Recovery and Climate Experiment (GRACE) gravimetry and ground-based Global Positioning System (GPS) measurements at the observation level can theoretically improve parameter accuracy. However, because of the implementation challenges, existing combination experiments are limited to low-degree (up to degree and order 20) gravity field determination or daily and weekly solutions. Here we present a one-step method for determining higher monthly gravity field solutions and the resulting models are up to degree and order 60. A comprehensive analysis of theoretical models and experimental results demonstrates the advantages of the one-step approach over the conventional two-step method, which processes ground and GRACE observations separately. Compared to two-step results, the one-step approach yields improvements in low-degree gravity field coefficients, with a 60 % improvement in the signal of the C20 coefficient. The polar motion x-component shows an average improvement of 58 %, while GPS satellite orbits achieved approximately 35 % reduction of Satellite Laser Ranging (SLR) residuals RMS. The GRACE satellite orbit exhibits a 22 % reduction in SLR residuals RMS for GRACE-A and 17 % for GRACE-B. In summary, the one-step method produces more consistent gravity and geometric products, improving the accuracy of shared parameters between ground-based and GRACE observations. (c) 2025 The Authors. Published by Elsevier B.V. on behalf of COSPAR. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

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.

The Earth’s time-variable gravity field is of great significance to study mass change within the Earth’s system. Since 2002, the NASA-DLR Gravity Recovery and Climate Experiment (GRACE) and its successor GRACE follow-on mission provide observations of monthly changes in the Earth gravity field with unprecedented accuracy and resolution by employing low-low satellite-to-satellite tracking (LLSST) measurements. In addition to LLSST, monthly gravity field models can be acquired from satellite laser ranging (SLR) and high-low satellite-to-satellite tracking (HLSST). The monthly gravity field solutions HLSST+SLR were derived by combining HLSST observations of low earth orbiting (LEO) satellites with SLR observations of geodetic satellites. Bandpass filtering was applied to the harmonic coefficients of HLSST+SLR solutions to reduce noise. In this study, we analyzed the performance of the monthly HLSST+SLR solutions in the spectral and spatial domains. The results show that: (1) the accuracies of HLSST+SLR solutions are comparable to those from GRACE for coefficients below degree 10, and significantly improved compared to those of SLR-only and HLSST-only solutions; (2) the effective spatial resolution could reach 1000 km, corresponding to the spherical harmonic coefficient degree 20, which is higher than that of the HLSST-only solutions. Compared with the GRACE solutions, the global mass redistribution features and magnitudes can be well identified from HLSST+SLR solutions at the spatial resolution of 1000 km, although with much noise. In the applications of regional mass recovery, the seasonal variations over the Amazon Basin and the long-term trend over Greenland derived from HLSST+SLR solutions truncated to degree 20 agree well with those from GRACE solutions without truncation, and the RMS of mass variations is 282 Gt over the Amazon Basin and 192 Gt in Greenland. We conclude that HLSST+SLR can be an alternative option to estimate temporal changes in the Earth gravity field, although with far less spatial resolution and lower accuracy than that offered by GRACE. This approach can monitor the large-scale mass transport during the data gaps between the GRACE and the GRACE follow-on missions.

重力恢复和气候实验(gravity recovery and climate experiment,GRACE)任务受限于卫星的低轨极地轨道性质和编队模式,确定的重力场模型C20项存在不足.与之相比,全球定位系统(global positioning system,GPS)卫星为倾斜轨道,卫星数量多,将G PS卫星的精密轨道数据作为伪观测值,使用动力学方法进行C20项确定的可行性研究.结果显示,2017年C20项时间序列的平均值比GRACE更接近卫星激光测距(satellite laser ranging,SLR)的结果,且不存在明显的约160 d的周期信号,表明利用GPS卫星解算C20项具有可行性.同时估计了光压模型P1参数,与GAMIT软件解算结果接近,进一步验证C20项解算结果的可靠性.

With ground-based synthetic aperture radar (GB-SAR) discontinuous observation, the effect of rail error, caused by multiple installations, on imaging is difficult to eliminate with difference correction. In this article, the impact of rail error on each point, which is related to the incident angle of each point, is theoretically analyzed. This is the first attempt to introduce a baseline in the application of GB-SAR microdeformation to build a model that estimates the incident angle of each point in the image. Then, the rail error correction model is established using the incident angle, and the influence of the rail error on the image point is weakened using this model. The experimental results show that the precision of the estimated incidence angle cosine is 0.0132, which is comparable to the same angle cosine value measured by the total station. By applying the correction method in this article, different impacts of each point in the image, caused by rail error from multiple instrument installations, can be weakened to below 0.1 mm, meeting the requirement of GB-SAR microdeformation measurement submillimeter accuracy.

The SuperSTAR accelerometers on GRACE satellites,which directly and precisely measure the non-gravitational forces,need to be calibrated by evaluating the scale and bias parameters.In this paper,the characteristics of pulse thrusting signal included in the accelerator observations are analyzed and their effect on accelerator calibration is discussed.Research based on the situ data of acceleration in April 2008 demonstrates that maximum effect of pulse thrusting on the calibrated scale parameter reaches 0.02,the calibrated bias parameter comes to 10-7 m· s-2,the calibrated acceleration amounts to 10-9 m·s-2,10 10 m·s-2 on the Y and Z axis respectively.

The modern satellite gravimetry missions have improved the mid-term and long wavelength parts of the earth gravity model significantly, and extended its usage in the scientific research in the relating subjects. The simultaneous solution method, which is one of the major methods used in the data processing for satellite gravimetry, is still under developing in China. Based on the basic model and some key technologies, especially on its relation with the kinematic orbit determination and the general dynamic method, the strategy on how to implement the simultaneous solution method is given in detail. And the real data from GRACE mission is analyzed with this method with the help of some work already done by our group. Some evaluations, including the external checks on the accuracy of the orbit, the analysis on the non conservative forces and the earth gravity model validation by the GPS/Leveling benchmarks are conducted. The numerical results show that the strategy on the realization of the simultaneous solution method is valid, and reveal its advantages distinctly. It is assumed that the key technologies of the simultaneous solution method have been solved, and an advance from the simulation stage to the real data analyzing is achieved. Finally, some prospects and future work are discussed to exert the potential ability of this method.

采用2009-11-01～2010-01-31三个月的SLR观测数据,对GOCE卫星运动学轨道PKI(precise kinematic orbit)进行检核.基于残差分析发现,SLR观测存在测站时距系统性偏差.消除测站时距偏差后,GOCE卫星PKI精密轨道的外符合精度达到1.5 cm.

研究了GRACE星载加速度计的动力法校准.联合精密轨道、星间距离变率同时估计重力场模型参数和加速度计校准参数,获得了SRF(satellite reference frame)下的比例系数和偏差参数时间序列,100阶重力场模型的大地水准面累积误差为4cm,在相应波段上优于CSR(center for space research)同时段的月重力场模型精度.以上述整体解算的结果为参照,对固定重力场模型参数的校准方案进行了检验,发现SRF框架下的非保守力差值最高可达10-8m·s-2量级,认为固定重力场模型的方法难以充分发挥GRACE加速度计的测量能力.本文研究结果可为后续的大规模卫星重力测量数据处理提供科学的依据,也能为开展相关科学滋补品应用提供可靠的非保守力数据.