在低对流层,传统的闭环模式容易造成较大的信号追踪误差.开环模式通过内部或外部方式消除导航资料调制(navigation data modulation,NDM)对大气反演的影响,能够准确地恢复信号的相位.内部和外部方式的区别是,前者通过信号相邻采样的内在联系移除NDM,后者利用卫星导航位元数据进行处理.通过内部和外部两种方式处理COSMIC(constellation observing system for meteorology,ionosphere and climate)掩星数据,利用全谱反演方法获得弯曲角,通过Abel积分变换计算折射率.COSMIC掩星个案分析表明,在低对流层,内部方式可能会导致信号的半周跳现象,从而造成反演的折射率出现误差.分别用上述两种方式对2007年第71天至73天共约3130个COSMIC掩星开环数据进行处理.将折射率反演结果与ECMWF(european centre for medium-range weather forecasts)分析场资料进行统计比较,结果显示:外部处理方式的探测深度比内部方式低100—200 m.在热带的3 km以下,内部方式具有比外部方式稍大的折射率负偏差.因此,外部方式能够得到比内部方式略优的反演结果.
The q-profile control problem in the ramp-up phase of plasma discharges is consid- ered in this work. The magnetic diffusion partial differential equation (PDE) models the dynamics of the poloidal magnetic flux profile, which is used in this work to formulate a PDE-constrained op- timization problem under a quasi-static assumption. The minimum surface theory and constrained numeric optimization are then applied to achieve suboptimal solutions. Since the transient dy- namics is pre-given by the minimum surface theory, then this method can dramatically accelerate the solution process. In order to be robust under external uncertainties in real implementations, PID (proportional-integral-derivative) controllers are used to force the actuators to follow the computational input trajectories. It has the potential to implement in real-time for long time discharges by combining this method with the magnetic equilibrium update.
