GRACE FIELD GEOPOTENTIAL COEFFICIENTS CSR RELEASE 6.0

FOR EXPERT USE ONLY. This dataset contains estimates of static field geopotential of the Earth, derived from the Gravity Recovery and Climate Experiment (GRACE) mission measurements, produced by the Center for Space Research (CSR) at University of Texas at Austin. The data are in spherical harmonics averaged over approximately a month. The primary objective of the GRACE mission is to obtain accurate estimates of the mean and time-variable components of the gravity field variations. This objective is achieved by making continuous measurements of the change in distance between twin spacecraft, co-orbiting in about 500 km altitude, near circular, polar orbit, spaced approximately 200 km apart, using a microwave ranging system. In addition to these range change, the non-gravitional forces are measured on each satellite using a high accuracy electrostatic, room-temperature accelerometer. The satellite orientation and position (and timing) are precisely measured using twin star cameras and a GPS receiver, respectively. Spatial and temporal variations in the gravity field affect the orbits (or trajectories) of the twin spacecraft differently. These differences are manifested as changes in the distance between the spacecraft, as they orbit the Earth. This change in distance is reflected in the time-of-flight of microwave signals transmitted and received nearly simultaneously between the two spacecraft. The change in this time of fight is continuously measured by tracking the phase of the microwave carrier signals. The so called dual-one-way range change measurements can be reconstructed from these phase measurements. This range change (or its numerically derived derivatives), along with other mission and ancillary data, is subsequently analyzed to extract the parameters of an Earth gravity field model.

仅限专业人士使用。本数据集包含地球静态位势场的估计值，该估计值源自重力恢复与气候实验（GRACE）任务测量结果，由德克萨斯大学奥斯汀分校空间研究中心（CSR）制作。数据以球谐函数形式呈现，并大约按月平均。GRACE任务的主要目标为获取重力场变化的平均值及时间变化分量的精确估计。此目标通过持续测量两颗共轨飞行、位于约500公里高度、近圆形极地轨道、间距大约200公里的双星航天器之间的距离变化来实现，测量使用的是微波测距系统。此外，通过高精度静电、室温加速度计对每颗卫星上的非引力力进行测量。利用双星相机分别精确测量卫星的朝向和位置（以及时间）。重力场的空间和时间变化以不同的方式影响双星航天器的轨道（或轨迹）。这些差异表现为航天器绕地球运行时距离的变化。这种距离变化反映在两航天器之间几乎同时发送和接收的微波信号的飞行时间上。通过跟踪微波载波信号的相位，连续测量这种飞行时间的变化。所谓的双单向距离变化测量可以通过这些相位测量重建。这种距离变化（或其数值导数）以及其他任务和辅助数据随后被分析，以提取地球重力场模型参数。