Nonlinear attitude tracking control for spacecraft formation with multiple delays

This paper addresses the attitude tracking control for spacecraft formation with delay free and communication delays. With help of the idea of sliding control, an adaptive attitude synchronization control architecture is established. Furthermore, by introducing a nonsmooth feedback function, a new class of nonlinear controllers for the attitude tracking of spacecraft is developed. Both parameter uncertainties and unknown external disturbances are dealt with via the kind of controllers. Finally, some simulation results are given to demonstrate the effectiveness and advantages of the proposed results.     

空中电场传感器

为了监测雷雨云下或云中电荷层的形成和演变,研制了一种空中电场传感器,它利用对金属定子采用交替屏蔽的原理来测量准稳态的大气电场。对仪器的工作原理,结构特点和技术指标作了较详细的介绍,并对该仪器的应用作了简短论述。     

箭载GPS信号传播误差改正模型的选优

误差修正模型是影响箭载GPS定位精度的关键问题之一。针对几种常用的GPS信号传播误差改正模型,探讨了各模型伪距延迟修正量的计算方法,分析和比较了各模型之间的差异,给出了组合误差修正模型的选优标准。实测数据计算结果表明,选优后的误差修正模型可有效提高目标定位精度。     

基于满意度分析的航班延误处置收益研究

通过研究社会属性和出行特征对旅客在面对航班延误,航班取消等的不同心理反应和行为特征,针对目前旅客满意度研究中基本是依靠评价指标体系进行宏观定量评价的研究现状,提出一种基于行为决策理论(微观心理学)的满意度动力学模型,定量分析大面积航班延误情景下旅客满意度的动态变化和不同措施组合对满意度的提升效果.同时,建立基于前景理论的旅客满意度收益模型,实现旅客满意度变化与航空公司收益的函数映射,通过实验分析不同延误服务组合对航空公司的收益影响,为航空公司提升旅客满意度,提升服务的时效性和针对性提供理论基础.     

An estimation of tropospheric corrections using GPS and synoptic data: Improving Urmia Lake water level time series from Jason-2 and SARAL/AltiKa satellite altimetry

Tropospheric correction is one of the most important corrections in satellite altimetry measurements. Tropospheric wet and dry path delays have strong dependence on temperature, pressure and humidity. Tropospheric layer has particularly high variability over coastal regions due to humidity, wind and temperature gradients. Depending on the extent of water body and wind conditions over an inland water, Wet Tropospheric Correction (WTC) is within the ranges from a few centimeters to tens of centimeters. Therefore, an extra care is needed to estimate tropospheric corrections on the altimetric measurements over inland waters. This study assesses the role of tropospheric correction on the altimetric measurements over the Urmia Lake in Iran. For this purpose, four types of tropospheric corrections have been used: (i) microwave radiometer (MWR) observations, (ii) tropospheric corrections computed from meteorological models, (iii) GPS observations and (iv) synoptic station data. They have been applied to Jason-2 track no. 133 and SARAL/AltiKa track no. 741 and 356 corresponding to 117–153 and the 23–34 cycles, respectively. In addition, the corresponding measurements of PISTACH and PEACHI, include new retracking method and an innovative wet tropospheric correction, have also been used. Our results show that GPS observation leads to the most accurate tropospheric correction. The results obtained from the PISTACH and PEACHI projects confirm those obtained with the standard SGDR, i.e., the role of GPS in improving the tropospheric corrections. It is inferred that the MWR data from Jason-2 mission is appropriate for the tropospheric corrections, however the SARAL/AltiKa one is not proper because Jason-2 possesses an enhanced WTC near the coast. Furthermore, virtual stations are defined for assessment of the results in terms of time series of Water Level Height (WLH). The results show that GPS tropospheric corrections lead to the most accurate WLH estimation for the selected virtual stations, which improves the accuracy of the obtained WLH time series by about 5%.     

GNSS receiver clock modeling when using high-precision oscillators and its impact on PPP

Processing data from Global Navigation Satellite Systems (GNSS) always requires time synchronization between transmitter and receiver clocks. Due to the limited stability of the receiver’s internal oscillator, the offset of the receiver clock with respect to the system time has to be estimated for every observation epoch or eliminated by processing differences between simultaneous observations. If, in contrast, the internal oscillator of the receiver is replaced by a stable atomic clock one can try to model the receiver clock offset, instead of estimating it on an epoch-by-epoch basis. In view of the progress made in the field of high-precision frequency standards we will investigate the technical requirements for GNSS receiver clock modeling at the carrier phase level and analyze its impact on the precision of the position estimates.     

Combination methods of tropospheric time series

In this article we present two methods for combination of different Global Navigation Satellite Systems (GNSS) Zenith Total Delay (ZTD) time-series for the same GNSS site, but from different producers or different processing setups. One method has been setup at ASI/CGS, the other at KNMI. Using Near Real-Time (NRT) ZTD data covering 1 year from the E-GVAP project, the performance of the two methods is inter-compared and validation is made against a combined ZTD solution from EUREF, based on post-processed ZTDs. Further, validation of the ASI combined solutions is made against independent ZTDs derived from radiosonde, Numerical Weather Prediction (NWP) model and Very Long Baseline Interferometry (VLBI) ZTD.     

基于免疫禁忌混合算法的航班快速恢复研究

为了减少枢纽机场大面积航班延误带来的经济损失，结合航班延误经济损失模型，在免疫进化算法的基础上，通过引入禁忌搜索进行优化改进，尝试用免疫禁忌混合算法解决航班延误恢复的问题。仿真实验结果表明，算法在航班快速恢复的问题中收敛速度和解的质量方面均优于标准遗传进化算法，既提高了航班恢复求解的效率，又减少了延误损失。     

The relationship between ionospheric total electron content (TEC) over East Asia and the tropospheric circulation around the Qinghai-Tibet Plateau obtained with a partial correlation method

This paper reports a study on the relationship between ionospheric total electron content (TEC) over East Asia and the tropospheric circulation around the Qinghai-Tibet Plateau. Ionospheric TEC over East Asia are obtained from 25 observatories during 1996–2004. By applying a partial correlation method which can eliminate the influences of solar and geomagnetic activities, we find no significant correlation between TEC and the Asian zonal circulation index (Iz), but find a positive correlation between the day-to-day variability of TEC and Iz. We suggest that the positive correlation is closely related with the topography of the Qinghai-Tibet Plateau. The dynamical effect on airflow of the plateau can generate vortexes, and the vortexes may continuously excite internal gravity waves (IGWs) which transmit up to the ionosphere and cause regional wave disturbances. This study gives evidence for the dynamical mechanism of ionosphere–troposphere coupling and shows the importance of the Qinghai-Tibet Plateau in the ionosphere–troposphere coupling over East Asia.