GRACE NON-TIDAL ATMOSPHERE AND OCEAN GEOPOTENTIAL COEFFICIENTS JPL RELEASE 5.0 GAC

FOR EXPERT USE ONLY. This dataset contains estimates of Earths geopotential field derived from the Gravity Recovery and Climate Experiment (GRACE) mission measurements and a non-tidal oceanic and atmospheric model produced by the Jet Propulsion Laboratory (JPL). 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 Earths 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 Earths 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.

仅供专业人士使用。本数据集包含由重力恢复与气候实验（GRACE）任务测量结果及喷气推进实验室（JPL）生产的非潮汐海洋和大气模型导出的地球位势场估算值。数据以球谐函数形式呈现，并大致按月平均。GRACE任务的主要目标是获取地球重力场变化的平均成分及时间变化成分的精确估算。此目标通过连续测量两颗在约500公里高度、近圆形极地轨道上共轨飞行的孪生航天器之间的距离变化来实现，两航天器相距大约200公里，并使用微波测距系统进行测量。此外，通过高精度静电、室温加速度计测量每个卫星上的非重力作用力。利用双星相机分别精确测量卫星的指向和位置（以及时间）。地球重力场的空间和时间变化以不同的方式影响双航天器的轨道（或轨迹）。这些差异表现为航天器绕地球飞行时距离的变化。这种距离变化反映在两航天器之间几乎同时发射和接收的微波信号的飞行时间上。通过追踪微波载波信号的相位，连续测量这种飞行时间的变化。所谓的双单程测距变化可以从这些相位测量中重建。这种测距变化（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。