基于激光扫描技术的大型船舶舱容量计量技术研究

介绍了一种应用三维激光扫描技术，采集获取船舱三维点云数据，对点云数据进行配准、修补，完成船舱内部构件精细建模，快速高精度的重建大型船舱三维模型，实现大型船舱容量快速计算的方法。运用三维激光扫描技术完成158000吨大型油轮液货舱容量计量，通过与传统容量计量方法进行比对分析，解决了单点数据采集模式弊端，达到了大型船舶舱容量快速、精准计量效果。     

Comparison of GPS derived TEC with the TEC predicted by IRI 2012 model in the southern Equatorial Ionization Anomaly crest within the Eastern Africa region

We have compared the TEC obtained from the IRI-2012 model with the GPS derived TEC data recorded within southern crest of the EIA in the Eastern Africa region using the monthly means of the 5 international quiet days for equinoxes and solstices months for the period of 2012 – 2013. GPS-derived TEC data have been obtained from the Africa array and IGS network of ground based dual-frequency GPS receivers from four stations (Kigali (1.95°S, 30.09°E; Geom. Lat. 11.63°S), Malindi (2.99°S, 40.19°E; Geom. Lat. 12.42°S), Mbarara (0.60°S, 30.74°E; Geom. Lat. 10.22°S) and Nairobi (1.22°S, 36.89°E; Geom. Lat. 10.69°S)) located within the EIA crest in this region. All the three options for topside Ne of IRI-2012 model and ABT-2009 for bottomside thickness have been used to compute the IRI TEC. Also URSI coefficients were considered in this study. These results are compared with the TEC estimated from GPS measurements. Correlation Coefficients between the two sets of data, the Root-Mean Square Errors (RMSE) of the IRI-TEC from the GPS-TEC, and the percentage RMSE of the IRI-TEC from the GPS-TEC have been computed. Our general results show that IRI-2012 model with all three options overestimates the GPS-TEC for all seasons and at all stations, and IRI-2001 overestimates GPS-TEC more compared with other options. IRI-Neq and IRI-01-corr are closely matching in most of the time. The observation also shows that, GPS TEC are underestimated by TEC from IRI model during noon hours, especially during equinoctial months. Further, GPS-TEC values and IRI-TEC values using all the three topside Ne options show very good correlation (above 0.8). On the other hand, the TEC using IRI-Neq and IRI-01- corr had smaller deviations from the GPS-TEC compared to the IRI-2001.     

Carrier phase prediction method for GNSS precise positioning in challenging environment

Since the signals of global navigation satellite system (GNSS) are blocked frequently in challenging environments, the discontinuous carrier phases seriously affect the application of GNSS precise positioning. To improve the carrier phase continuity, this paper proposes a carrier phase prediction method based on carrier open-loop tracking. In the open-loop tracking mode, the carrier numerically controlled oscillator (NCO) is controlled by the predicted Doppler, but not by the loop filter output. To improve the phase prediction effective time, accurate receiver clock drift estimation is studied in the prediction method. The phase prediction performance is tested on GNSS software receiver. In the phase prediction effective time tests, open-loop processes were set for the tested channel. The test results show that, when some satellite signals are blocked in 15?s, the probability of carrier phase error less than quarter cycles is more than 94%. In the real time kinematic (RTK) positioning tests, some satellite signals are blocked in 10–15?s repeatedly. The test results show that, the carrier phase continuity is basically not affected by the signal interruption, and the RTK can almost keep continuous centimeter-level positioning accuracy without re-fixing the integer ambiguity.     

Factor graph based navigation and positioning for control system design: A review

Navigation and positioning is an important and challenging problem in many control engineering applications. It provides feedback information to design controllers for systems. In this paper, a bibliographical review on factor graph based navigation and positioning is presented. More specifically, the sensor modeling, the factor graph optimization methods, and the topology factor based cooperative localization are reviewed. The navigation and positioning methods via factor graph are considered a...     

GPS/伪卫星组合定位中伪卫星改进选址模型

为了更为有效地改善GPS卫星的几何结构,提高GPS/伪卫星组合定位的精度,在推导伪卫星增强GPS系统基本公式的基础上,阐述了GPS绝对定位精度因子的相关理论,说明了引入伪卫星的必要性;提出了建立以观测时间、高度角和方位角为自变量,绝对定位精度因子为因变量的四维选址模型,并采用一次性添加伪卫星方式,改进现有的逐颗添加方式,建立了整体最优的伪卫星选址模型,给出了该模型的工作流程。以空间位置精度因子PDOP为例,进行实测数据测试与分析,结果表明：基于两种伪卫星添加方式建立的四维模型均可为高效的伪卫星选址工作提供可靠依据,实现伪卫星的优化选址;其中一次性添加方式优于逐颗添加方式,尤其对于添加2颗伪卫星,PDOP值在局部的优化程度达到了1.0以上,较大程度地改善了逐颗添加伪卫星方式产生的不利区域,可以提供更为有效的伪卫星选址方案。     

基于经验模分解的PPP时间比对数据消噪方法

精密单点定位(PPP)时间比对数据会受到观测噪声的影响,因此对时间比对数据进行消噪是一项重要工作。提出一种基于经验模分解(EMD)的PPP时间比对数据消噪方法,并将该方法与Vondrak滤波方法的消噪效果进行对比。结果表明,两种方法的消噪效果相当,均能有效滤除PPP时间比对数据中的随机噪声,明显改善时间比对的稳定度。     

Optimization of geosynchronous satellite constellation for independent regional navigation and positioning in Middle East region

Regional Navigation and positioning systems using geosynchronous satellites are emerging for different parts of the world. Optimal constellation geometry achievement for a set of geosynchronous satellites is a key sector in designing of such systems. Genetic algorithm is applied for optimization of constellations with 6 and 7 satellites which is to be used in Middle East region where these systems have been deprived of. Based on the fact that the coverage criterion is not sufficient enough to guarantee a good navigation service, positioning process by the satellite systems is discussed and the performance of the system on the basis of position dilution of precision is collected as the fitness criterion. Placing the satellites in groups to pass over the same ground track is applied as a constraint to the genetic algorithm. By simulation, performance of the best obtained results and GPS are compared in terms of position dilution of precision, visibility and the required epochs (time span) to resolve the ambiguities with a 99% success rate, in this region. Also, capability of the GA for such problems is demonstrated.     

The impact of orbital errors on the estimation of satellite clock errors and PPP

Precise satellite orbit and clocks are essential for providing high accuracy real-time PPP (Precise Point Positioning) service. However, by treating the predicted orbits as fixed, the orbital errors may be partially assimilated by the estimated satellite clock and hence impact the positioning solutions. This paper presents the impact analysis of errors in radial and tangential orbital components on the estimation of satellite clocks and PPP through theoretical study and experimental evaluation. The relationship between the compensation of the orbital errors by the satellite clocks and the satellite-station geometry is discussed in details. Based on the satellite clocks estimated with regional station networks of different sizes (∼100, ∼300, ∼500 and ∼700 km in radius), results indicated that the orbital errors compensated by the satellite clock estimates reduce as the size of the network increases. An interesting regional PPP mode based on the broadcast ephemeris and the corresponding estimated satellite clocks is proposed and evaluated through the numerical study. The impact of orbital errors in the broadcast ephemeris has shown to be negligible for PPP users in a regional network of a radius of ∼300 km, with positioning RMS of about 1.4, 1.4 and 3.7 cm for east, north and up component in the post-mission kinematic mode, comparable with 1.3, 1.3 and 3.6 cm using the precise orbits and the corresponding estimated clocks. Compared with the DGPS and RTK positioning, only the estimated satellite clocks are needed to be disseminated to PPP users for this approach. It can significantly alleviate the communication burdens and therefore can be beneficial to the real time applications.     

Unscented Kalman滤波在空间飞行器被动测距中的应用

介绍了Unscented Kalman滤波及其空间飞行器被动测距中的应用。Unscented Kalman滤波通过设计少量的sigma(抽样)点,计算这些点经过非线性函数的传播,获得滤波值基于非线性方程的更新。Unscented Kalman滤波避免了广义Kalman滤波等线性化方法的缺点,并提高了滤波精度。     

GPS不完整星座定位方法研究

为了提高钟差预测模型辅助接收机定位解算的效果,从灰色系统的角度对接收机钟差序列进行探讨,提出了基于灰色理论的钟差预测模型。文中首先给出了新模型的基本思想和具体实现步骤,然后将基于该模型的钟差预测值引入到GPS接收机中,辅助接收机在不完整星座条件下实现定位解算。基于GPS实测数据的验证分析表明,新模型不仅对钟差序列具有很好的预测效果;而且提高了接收机定位的连续性和可靠性,在仅有3颗卫星的条件下可以实现三维定位。同时,新方法无需增加额外设备,辅助方式简单方便,经济灵活。