A new method to mitigate multipath error in single-frequency GPS receiver with wavelet transform

One of the major errors in high-precision GPS positioning is multipath. Multipath effect modeling and reduction have been a challenging issue in high-accuracy GPS positioning applications due to its special properties. Different methods have been employed to mitigate this error including hardware and software approaches. We reduce C/A code multipath error by adopting an efficient software method which uses wavelet transform as a basic data processing trend. The key idea of the proposed method is using stationary wavelet transform (SWT) in GPS signal data processing. Since we have used SWT, there is complete access to high-frequency and low-frequency terms in both time and frequency domains, and we can apply appropriated procedures to mitigate this error. The multipath error mostly is a low-frequency term. In our proposed method, the double difference (DD) residuals are applied to the SWT to identify the multipath disturbance. The extracted multipath is then used to correct DD observations. Our experiments include three data sets to investigate the proposed method and compare it with existing algorithms. We used simulations for two of these data sets. The results indicate the efficiency of the proposed method over existing algorithms.     

利用单基准站改正信息和电离层参数估计的单频PPP算法

利用单个基准站提供的改正信息对流动站的单频观测值数据进行改正,同时引入电离层参数进行实时电离层延迟估计,进行单频精密单点定位（PPP）计算。相比传统的单频PPP方法,本文方法对单频PPP的收敛速度和定位精度都有很大的提高,定位精度优于2cm,且受基准站距离的影响较小。     

内置ARM板卡GPS接收机设计与实现

随着信息化科技的不断发展,GPS在很多领域得到了广泛的应用.本文以GPS系统为蓝图,用ARM板卡技术作为平台设计了嵌入式GPS接收机,并对接收的动态试验数据精度进行分析,证明了基于ARM板卡的嵌入式GPS接收机在GPS系统中应用的可行性.     

地基GPS与掩星联合的电离层层析成像方法研究

由于有限视角、稀疏布站等原因,地基G PS电离层层析成像存在垂直分辨率不高的问题,联合掩星进行电离层层析成像是一个重要的解决途径。一方面地基G PS观测能保证电离层层析成像的时间连续性和区域覆盖性;另一方面由于掩星信号能够提供地基G PS没有的水平射线信息,提升了电离层层析成像的垂直分辨率水平。利用地基GPS站与COSMIC卫星的掩星观测进行的仿真结果表明：与仅利用地基G PS相比,联合掩星进行电离层层析成像,不仅在电离层电子密度反演精度方面有明显提升,而且在电离层F2层峰值高度（hm F2）和电离层总电子含量（T EC ）的精度方面同样有明显提高。     

Real time estimation of position and the gravity vector with an inertial survey system

Based on sine functions for fitting horizontal velocity errors in an inertial survey system and a step or slope function approximation of the vertical deflection between stops, a positioning accuracy of 10 m (CEP) can be achieved with a car-borne system – a modified -21 aircraft navigation system, with a 10 min travel period between Zero Velocity Update Times (ZUPTs) and a total 1.5 hour survey time. A rough estimation of the vertical deflection can also be expected in real time out of the approach. Also a forward-backward-forward run is presented which demonstrates determination of the gravity anomaly. Received 10 March 1995; Accepted 8 July 1996     

精密单点定位估计GPS卫星的P1-C1码偏差及稳定性分析

给出了利用精密单点定位（PPP）技术估计GPS卫星P1-C1码偏差的数学模型,并以BRUS、GODE、SHAO和NIST四个跟踪站2010年10月份一个月的观测数据为例,采用PPP方法计算了所有GPS卫星的P1-C1码偏差,并与欧洲定轨中心提供的P1-C1码偏差进行了比较,结果表明：四个站估计的P1-C1码偏差精度均可达到几个厘米。一个月的计算结果表明：卫星的P1-C1码偏差在一个月内变化平缓。     

Influence of clock jump on the velocity and acceleration estimation with a single GPS receiver based on carrier-phase-derived Doppler

Since the Selective Availability was turned off, the velocity and acceleration can be determined accurately with a single GPS receiver using raw Doppler measurements. The carrier-phase-derived Doppler measurements are normally used to determine velocity and acceleration when there is no direct output of the raw Doppler observations in GPS receivers. Due to GPS receiver clock drifts, however, a GPS receiver clock jump occurs when the GPS receiver clock resets itself (typically with 1 ms increment/decrement) to synchronize with the GPS time. The clock jump affects the corresponding relationship between measurements and their time tags, which results in non-equidistant measurement sampling in time or incorrect time tags. This in turn affects velocity and acceleration determined for a GPS receiver by the conventional method which needs equidistant carrier phases to construct the derived Doppler measurements. To overcome this problem, an improved method that takes into account, GPS receiver clock jumps are devised to generate non-equidistant-derived Doppler observations based on non-equidistant carrier phases. Test results for static and kinematic receivers, which are obtained by using the conventional method without reconstructing the equidistant continuous carrier phases, show that receiver velocity and acceleration suffered significantly from clock jumps. An airborne kinematic experiment shows that the greatest impact on velocity and acceleration reaches up to 0.2 m/s, 0.1 m/s² for the horizontal component and 0.5 m/s, 0.25 m/s² for the vertical component. Therefore, it can be demonstrated that velocity and acceleration measurements by using a standalone GPS receiver can be immune to the influence of GPS receiver clock jumps with the proposed method.     

中国-日本绝对重力仪器测量比对结果

本文给出了中科院测地所FG5-112和日本京都大学FG5-201及日本国土地理院FG5-104等几台绝对重力仪在武汉九峰和香港天文台绝对重力测量比对结果。分析说明不同仪器间具有良好的一致性,其中FG5-112与FG5-104结果间的互差达8×10-8m/s2;FG5-112与FG5-201和FG5-104等的观测互差小于2×10-8m/s2。这种比对观测,可为深入了解仪器性能和精确测定不同台站重力非潮汐变化提供可靠参考。     

Investigation and validation of two all-weather land surface temperature products with in-situ measurements

The need for cross-comparison and validation of all-weather Land Surface Temperature(LST)products has arisen due to the release of multiple such products aimed at providing compre-hensive all-weather monitoring capabilities.In this study,we focus on validating two well-established all-weather LST products(i.e.MLST-AS and TRIMS LST)against in-situ measure-ments obtained from four high-quality LST validation sites:Evora,Gobabeb,KIT-Forest,and Lake Constance.For the land sites,MLST-AS exhibits better accuracy,with RMSEs ranging from 1.6 K to 2.1 K,than TRIMS LST,the RMSEs of which range from 1.9 K to 3.1 K.Because MLST-AS pixels classified as\"inland water\"are masked out,the validation over Lake Constance is limited to TRIMS LST:it yields a RMSE of 1.6 K.Furthermore,the validation results show that MLST-AS and TRIMS LST exhibit better accuracy under clear-sky conditions than unclear-sky conditions across all sites.Since the accuracy of the all-weather LST products is considerably affected by the input clear-sky LST products,we further compare the all-weather LST with the correspond-ing input clear-sky LST to conduct an error source analysis.Considering the clear-sky pixels on MLST-AS directly using the estimates from MLST,the error source analysis is limited to examining TRIMS LST and its input(i.e.MODIS LST).The findings indicate that TRIMS LST is highly correlated with MODIS LST.The investigation and validation of the two selected all-weather LST products objectively evaluate their accuracy and stability,which provides impor-tant information for applications of these all-weather LST products.     

台风“尼伯特”的电离层扰动分析

针对台风运动过程中大气层与电离层的耦合效应问题,该文采用总电子含量与电子密度数据分析了台风"尼伯特"达到最大风速时刻的电离层变化情况。结果显示在台风达到最大时刻的当天,风眼处电离层电子含量显著降低,在台风附近的IGS测站处也有明显的电子含量负异常出现。电子含量异常空间分布图显示最大异常区域位于风眼的南侧,表明台风边缘处的电离层异常幅度要大于风眼处的异常幅度。电子密度三维模型显示在250～350km高度上,风眼附近有显著电子密度减弱现象,尤其在300km高度上,异常幅度达到-6～-8×105 el/cm3。诸多证据表明此次电子含量负异常与台风"尼伯特"造成的大气层-电离层耦合效应有关,这可为以后的台风-电离层扰动研究提供一定的参考。     

LIDAR与DMC结合的无地面控制的航测新方法

LIDAR开辟了由空中直接获取高精度三维地面信息的新途径,获取数据的速率和精度大大提高,数据的应用范围更加广泛。DMC影像具有高分辨率,色调饱满,影像清晰、洁净,具有比传统扫描摄影胶片获得的影像具有更好的品质。本文介绍LIDAR与DMC的综合应用,提出一种无地面控制的航测新方法,能够经济而快速,高精度地获得测区的现势4D产品,对研究二者的综合应用有一定的参考意义。