星载加速度计频域噪声对时变重力场反演的影响研究

Study on the influence of frequency-dependent accelerometer noise in determining temporal gravity field model

星载加速度计是低低卫星跟踪卫星测量的核心载荷之一,其观测噪声受仪器本身和观测环境的综合影响.本文综合考虑加速度计仪器的研制能力和观测环境,系统分析了不同频率特性的加速度计噪声对时变重力场反演精度的影响.首先,下一代重力卫星推行的加速度计频域噪声明显小于GRACE卫星搭载的加速度计,但受限于背景力模型误差的影响,其反演重力场模型精度的提升幅度小于2%.其次,受卫星飞行过程中温度和磁场等周期性变化的影响,加速度计观测数据中存在固定频率的音调误差,在同类型、大小的音调误差下,径向和沿轨方向的音调误差对重力场精度的影响显著,而法向方向影响较小;以能否提取空域内的时变信号为限制条件,径向和沿轨方向的音调误差应小于10-8m·s^(-2),而法向方向可放宽至10-7m·s^(-2);为了削弱时变重力场模型南北条带误差的影响,应该约束加速度计高频音调误差的影响.最后,探讨了三轴敏感加速度计对重力场反演精度的潜在贡献,由于重力场反演精度与加速度计法方向观测精度的响应关系相对较弱,三轴敏感加速度计仅能提升约2%的重力场反演精度.研究结果表明,由于加速度计频域噪声与重力场反演精度存在复杂的响应关系,在重力卫星研制或观测数据处理过程中,不能仅仅考虑加速度计的噪声水平,还应该充分考虑加速度计在频域内各类噪声特性的影响.

On-board accelerometer is one of the key payloads for low-low satellite-to-satellite tracking mission,while its accuracy is seriously affected by the accelerometer noise level as well as the observational environment.In this study,we designed various accelerometer noise scenarios by comprehensively considering the accelerometer manufacture ability and observational environment,and further assessed the impact of frequency dependent accelerometer noise on temporal gravity field model determination.Firstly,the accelerometer noise of next generation gravity mission(NGGM)is significantly smaller than the GRACE-type accelerometer in frequency domain.However,due to the limitation of background force model errors,there is only about 2%improvement in terms of the corresponding retrieved gravity field model.Secondly,due to the periodic variations of temperature and magnetic field,there are tone errors with the integer multiples of the orbit frequency in accelerometer observations.Among the tone errors with the same type and same noise level,those in radial and along-track direction seriously affect the accuracy of temporal gravity field model,while the affect in cross-track direction is minor.If one want to obtain the sensible temporal gravity signals with reasonable north-south stripe errors,the tone errors should be limited to at least 10-8m·s^(-2) in radial and along-track direction,while the limitation can extend to 10-7m·s^(-2).Meanwhile,to reduce the stripe errors in spatial domain,the tone errors at high frequency should be carefully limited.Finally,the potential improvements derived from the three-axis sensitive accelerometer are discussed.However,since the minor effect of accelerometer noise in cross-track direction,the introduce of three-axis sensitive accelerometer can only improve the temporal gravity field model within 2%.Our results demonstrate that,during designing the satellite gravity mission or processing in-situ observations,we should not only consider the impact of accelerometer noise level,but also sincerely take the frequency dependent accelerometer noise into account.