In this study, the TECs derived from three well-established climatology models including IRI-2012 (International Reference Ionosphere), SPIM2014 (Standard Plasmasphere-Ionosphere Model), and NIC09 (New Ionosphere Climatology) were evaluated with IGS final TEC maps in spatial and temporal domains. It was found that NIC09 overestimated TECs slightly with respect to IGS results. The RMSE over all seasons was about 4 TECu. That was greater in winter than in other seasons. SPIM-2014 overestimated TECs greatly. There were spring and autumn anomalies, with the autumn anomaly more obvious. The RMSE was approximately 8 TECu. IRI-2012 underestimated TECs during all seasons except in autumn. The RMSE was nearly 7 TECu except in winter. In terms of the latitude dependence, the performance of the three models was better in middle and high latitudes than in low latitudes (especially equatorial regions). The performance of NIC09 was generally the best, followed by IRI-2012 and SPIM-2014. The performance of IRI-2012 was mostly better than SPIM-2014 except in summer in the northern hemisphere and winter in the southern hemisphere. The finding in this study could provide references for the specific application of ionospheric climatology models.

Ionospheric total electron content (TEC) is the key factor for the media correction in Space Geodesy application. Ionospheric climatology models could provide TEC estimations. In this study, TECs hourly computed by three climatology models (IRI–2012, SPIM–2014 and NIC09) were validated by IGS final TEC maps in spatial and temporal domains. It was found that NIC09 overestimated TECs slightly with respect to IGS results. The accuracy during seasons was about 4 TECu. That was worse in winter than other seasons. SPIM–2014 overestimated TECs greatly. There were spring and autumn anomalies with the autumn anomaly more obvious. The accuracy was approximately 8 TECu. IRI–2012 underestimated TECs during all seasons except in autumn. The accuracy was nearly 7 TECu except in winter. As for the latitudinal domain, the performance of three models was better in middle and high latitudes than in low latitudes (especially equatorial regions). Overall, the accuracy of NIC09 was highest, which was followed by IRI–2012 and SPIM–2014. The accuracy of IRI–2012 was mostly better than SPIM–2014 except in summer north hemisphere and winter south hemisphere. The finding in this study could provide references for the specific application of the ionospheric climatology models.

In this paper, we present the design and deployment of a broadband interferometric mini array. The network with five electromagnetic signal detectors deployed over an area about 1 km2 is applied here to record 20‐ to 70‐kHz vertical electric fields emitted by radio transmitters in very low frequency/low‐frequency band. Furthermore, interferometric imaging algorithm is employed to evaluate the elevation angles and azimuth angles of the electromagnetic radiation source. It is found that the deviation between expected azimuth and the mean value of calculated azimuth is less than 0.2° with standard deviation of 3.55°. The experiment results indicate that the mini array may provide benefits in determining the precise locations of electromagnetic radiation sources.

This study carries out a quantitative analysis of the performance of ionospheric tomography in the topside ionosphere, utilizing data of October 2011 collected from 260 Global Navigation Satellite System (GNSS) stations in the Crustal Movement Observation Network of China. This tomographic reconstruction with a resolution of 2° in latitude, 2° in longitude and 20 km in altitude has more than 70 % of voxels traversed by GPS raypaths and is able to provide reliable bottom parts of ionospheric profiles. Compared with the observations measured by the Defense Meteorological Satellite Program (DMSP) satellites (F16, F17 and F18) at an altitude of 830–880 km, the results show that there is an overestimation in the reconstructed plasma density at the DMSP altitude, and the reconstruction is better during daytime than nighttime. In addition, the reconstruction at nighttime also indicates a solar activity and latitudinal dependence. In summary, with respect to DMSP measurements, the daytime bias is on average from −0.32 × 105/cm3 to −0.28 × 105/cm3, while the nighttime bias is between −0.37 × 105/cm3 and −0.24 × 105/cm3, and the standard deviation at daytime and at nighttime is, respectively, 0.082 × 105/cm3 to 0.244 × 105/cm3 and 0.086 × 105/cm3 to 0.428 × 105/cm3. This study suggests that vertical ionospheric profiles from other sources, such as ionosondes or GNSS occultation satellites, should be incorporated into ground-based GNSS topside tomographic studies.

Currently,the GNSS network of Yangtze River delta has being applied to monitor the water vapor above this region and research water vapor tomography.Studies have shown that the dictances between stations are large and inhomogeneous,that will make it difficult to get the high tomography precision.Therefore,a simulation test of multi GNSS observations on tomography is introduced.The multi GNSS observations are more homogeneous in spatial distribution than a single positioning system,which can reduce the space rate of the grid,especially increase the number of the grid with information at middle and high layers.The multi GNSS observation can provide more and better water vapor information which can patch up deficiency of a single positioning system.A simulated water vapor tomography is carried out, and the result shows that the multi GNSS observations could improve the accuracy of tomography, especially above the 5 km height layer of the atmosphere.

利用中国地壳运动监测网络CMONOC中85个测站的GPS观测数据,建立3种常用的区域电离层模型:多项式函数模型(polynomial model,POLY)、低阶球谐函数模型(low-degree spheric function model,LSF)和球冠谐函数模型(spheric cap harmonic model,SCHA),并利用数字测高仪和GPS实测数据对3个模型进行评估和比较.与数字测高仪数据的比较表明,3个模型能够较为准确地反映VTEC的变化趋势,证明了模型的有效性.与GPS实测数据的比较表明,3个模型中平均精度最高的是低阶球谐函数模型,其次是多项式模型,最后是球冠谐模型,其RMS和STD平均值依次为3.48 TECu、3.03 TECu、3.54 TECu、3.00TECu、3.82 TECu、3.25 TECu.利用GPS实测数据计算GIM(global ionospheric maps)模型的精度,结果显示,3个模型的BIAS均比GIM模型大,但是其RMS和STD小于GIM模型,显示了区域模型精度较高的稳定性.由各个模型与GIM模型的VTEC差值格网图可知,3个模型在建模区域的中部精度较高,多项式模型在边界有较明显的边际效应.

With the increased number of Galileo navigation satellites joining the Global Navigation Satellite Systems (GNSS) service, there is a strong need for estimating their differential code biases (DCBs) for high-precision GNSS applications. There have been studies for estimating DCBs based on an external global ionospheric model (GIM) proposed by Montenbruck et al. (2014). In this study, we take a different approach by joining the construction of a GIM and estimating DCB together with multi-GNSS observations, including GPS, the BeiDou navigation system, and the Galileo navigation system (GAL). This approach takes full advantage of the collective strength of the individual systems while maintaining high solution consistency. Daily GAL DCBs were estimated simultaneously with ionospheric model parameters from 3 months' multi-GNSS observations. The stability of the resulting GAL DCB estimates was analyzed in detail. It was found that the standard deviations (STDs) of all satellite DCBs were less than 0.17 ns. For GAL receivers, the STDs were greater than for the satellites, with most values <2 ns. Comparison of the statistics of time-ranged stability of satellite DCBs over different time intervals revealed that the difference in STD between 28 and 7 day intervals was small, with the maximum not exceeding 0.01 ns. In almost all cases, the difference in GAL satellite DCBs between two consecutive days was <0.8 ns. The main conclusion is that based on the stability of the GAL DCBs, only occasional calibration is required. Furthermore, the 30 day-averaged satellite DCBs may satisfy the requirement of high-precision applications depending on the GAL satellite DCBs.

介绍了2011年中国科学院新疆天文台南山站GPS和25 m VLBI天线的归心测量方案、局域三角测量网、高程控制网与靶标交会测量方法及资料解算.利用测量数据,首次建立了南山GPS与VLBI空间大地测量技术并置站本地连接参数,测量精度优于1 mm.

新疆天文台南山GPS观测站是国内、国际建立和维持ITRF进行全球动力学研究的参考点之一，由于其测站的特殊地理位置，测站的GPS观测受到国际及国内相关学者的重视。为了确保测站GPS观测数据的精度，对观测数据进行质量评定。选取2012-11-15~12-15 GUAO站GPS观测数据进行统计分析，重点分析了信噪比的强弱及多路径效应对观测数据的影响。

借助当前比较完善的GPS系统,建立基于BDS/GPS双系统的全球电离层模型,是克服BDS单系统建模弊端,提高全球电离层模型和硬件延迟(DCB)监测精度的一种有效途径.本文分析了基于BDS/GPS双系统的电离层模型所能达到的精度,以及GPS观测对DCB监测的辅助作用.文中选用了太阳活动峰年2013年2月11日-2014年1月13日336天的BDS/GPS双系统观测资料,利用15×15阶球谐函数模型建立了全球电离层模型(GIM/SHA),并利用IGS最终电离层产品(GIM/IGS)、双频实测VTEC和海洋测高数据对该双系统模型的电离层产品进行了全面的精度评估.结果表明:(1)通过与三种基准数据比对,GIM/SHA的外符合精度在3-6 tecu范围内,且系统性偏差较小;(2) GPS卫星P1P2频点DCB与IGS最终产品结果比较BIAS在0.1 ns内,RMS最大不超过0.2 ns;(3)通过比较BDS单系统与双系统生成的卫星和接收机B1B2频点DCB发现,两种方法解算的DCB均值差别为0.01-0.227 ns,双系统解算BDS卫星DCB稳定性稍优于单系统结果,但是GPS观测资料的加入能够明显地提高接收机DCB的稳定性;从14颗BDS在轨卫星B1B2频点DCB长期稳定性统计可见,各卫星DCB长期稳定性为0.2-0.3ns,其中GEO卫星稳定性水平稍差.

由于难以精确模制,太阳辐射压摄动已经成为导航卫星精密定轨的主要误差源.因此,为了提高导航卫星的定轨精度,必须对太阳辐射压进行精确建模.随着我国北斗卫星导航系统的稳定运行,开发适用于北斗卫星的太阳辐射压模型已经成为一个研究热点.通过回顾国内外近几十年的太阳辐射压模型研究成果,详细介绍了几种常用的太阳辐射压模型,对其建模原理以及模型的优缺点进行了分析,并介绍了北斗卫星太阳辐射压建模的研究现状,为我国北斗卫星导航系统的太阳辐射压建模提供借鉴.

The tropospheric delay is one of the most significant error sources for radio navigation and space geodetic techniques. Its value is seriously affected by the height of the observing object. Due to the requirement of real-time capability and the drastic variations in the height of the object, there are various defects in existing tropospheric delay models for calculating the delay in kinematic navigation and positioning. Based on the vertical profiles of zenith tropospheric delay (ZTD) derived from ERA-Interim reanalysis data in 2005 and 2006, as well as it's hydrostatic and non-hydrostatic components (ZHD and ZWD), the optimal fitting method of ZTD with respect to height was studied and a new global ZTD model which is referred to as SHAG-H was established. The SHAG-H model is built on the variation of water vapor in the vertical atmosphere and represents ZTD as a piecewise function of height. Then the variations of parameters in each function with respect to time are modeled. The most of mean bias between the SHAO-H ZTD and the integral ZTD at different isobaric layers are within +/- 1 mm, while the RMS reduces from 39 mm to less than 1 mm with the increase of height. Compared with International GNSS Service (IGS) ZTD at 117 global stations in 2011, the SHAO-H model (the bias is 7.02 mm, the RMS is 38.50 mm) is superior to the UNB3m model (the bias is 14.67 mm, the RMS is 51.95 mm). The SHAO-H model we constructed has many advantages such as consistency in accuracy and simplicity in computation, which is suitable for the users at arbitrary height in the neutral atmosphere.

Meteorological parameters are needed when ground-based GPS is used for the detection of PWV(precipitable water vapor).However,a large amount of GPS data has not been sufficiently used because of the lack of related meteorological data.In this paper,the methods and feasibility of deriving meteorological parameters from ERA-Interim reanalysis data and calculating GPS/PWV with the extracted parameters in China are assessed.The atmospheric pressure,temperature and relative humidity derived from ERA-Interim are compared with meteorological observation data at 24meteorological stations from 2006to 2007,and the GPS/PWV calculated from the two data sets are also contrasted.Results are as follows:① Atmospheric pressure derived from upper-air reanalysis data,temperature and relative humidity derived from surface reanalysis data,has relatively high precision.② The reanalysis parameters and meteorological observation data comparisons at 24stations show a mean bias of 0.08hpa and a RMSD of 0.85hpa with atmospheric pressure,a mean bias of 0.05Kand a RMSD of 2.45Kwith temperature,a mean bias of 2.82%and a RMSD of 14.75% with relative humidity.③ The ERA-Interim reanalysis data is more reliable in the east of China than in the west.The precision of temperature and relative humidity data show seasonal variation.④ As compared with GPS/PWV calculated by the meteorological observation data,the GPS/PWV calculated by the ERAInterim data give a mean difference of less than 0.5mm and a RMSD of less than 1mm.

Tropospheric delay is a major source of error for ground-to-air, air-to-ground observation and various types of radio navigation positioning technology, and it is usually corrected by tropospheric delay models for the majority of real-time navigation users. Traditional tropospheric delay models (such as Hopfield, Saastamonion, UNB3, etc.) take the cumulative delay of the whole atmosphere into account, and surface meteorological data is needed as the input to some of them. It's hard to meet the requirement of the atmospheric delay correction for the real-time user at arbitrary time and height by using the old models. We consequently adopt the method modeling the zenith tropospheric delay (ZTD) with the altitude directly to solve this problem. In this paper, the ZTDs at different altitude were calculated by the ERA-Interim reanalysis data in 2004 at 1.5 grid points, and the spatiotemporal characteristics of ZTD varying with altitude was studied detailedly. A fitting analysis between ZTD and altitude was carried out by a piecewise function afterwards. The accuracy of the fitting function above was assessed carefully, and we also tested it by the ZTDs come from 45 IGS (International GNSS Service) stations distributed all over the world from 2008 to 2010. The results are as following: The deviation of the fitting and the integral ZTDs come from ERA-Interim is less than 1 cm at all the grid point, and which is stable in the range of 45 km high. The fitting and IGS ZTDs comparisons at 45 stations show a mean yearly difference of no more than 1 cm with a mean SD of about 4.3 cm. The piecewise fitting function we constructed could be applied as a preliminary model of the ZTD varying with altitude, and has important application value in real-time navigation and positioning. © 2013 Springer-Verlag Berlin Heidelberg.

The distribution of GPS slant observations taken by continuously operating Yangtze River Delta GPS network this work is described.The distribution of the grid coverage of slant data at different temporal and spatial resolutions are given.From this,the feasibility of 3D water vapor tomography in a test region is discussed.At last,a set of additional instruments in GPS network scheme for water vapor tomography is researched by using simulation method with ECMWF data.It is concluded that the bad geographic distribution of GPS network in Yangtze River Delta causes difficulties in tomography,and the overall accuracy can be improved by adding some stations,especially in lower atmosphere.

新疆天文台同时拥有 GPS 与 VLBI 空间大地测量技术,是国际、国内 VLBI 观测网与 GPS 观测网的重要观测台站之一.本文介绍了2011年中科院新疆天文台南山观测站首次进行 GPS 与 VLBI25米射电望远镜的本地连接测量,文中着重介绍了本地连接的控制网的布设、观测方法以及数据处理方法.

Since IGS ionosphere working group(IONO_WG) was established in 1998, ionosphere products have been supplied routinely with the form of IONEX maps. The final IONEX map has the precision of about 2-8TECu in the whole world given by the ionosphere validation center. Due to at most six IGS GPS stations in China used to retrieve global ionosphere model(GIM), the precision of the GIM applied to China is not the same as to Europe and USA, which has to be evaluated for all kinds of users in this area. The CMONOC(Crustal Movement Observation Network of China) has been constructed with 260 GPS stations and other instruments, which can provide very nice conditions for us to model the ionosphere more precisely in China area. In this article, we choose about 200 GPS stations from CMONOC and several hundreds of IGS stations over different periods of 2011, which is in the rising period of sun activity, to model the global ionosphere, and GIM from CODE in china region can be assessed with this more exact model. By analysis on the applied precision of CODE GIM over China, we have a conclusion: 1) there is a bias of 2-4TECu, RMS of 2-4TECu, and STD of 1-2TECu under the magnetic quiet circumstances and the bias is about 5.1TECu, RMS is about 5.7TECu and STD is about 2.4TECu under the magnetic disturbances circumstances. 2) for the situations at the specific time of ionosphere changes within one day( local time 14h and 22h), bias of the former situation is in the range of 2-4TECu while that of latter is in the range of 2-5TECu under normal circumstances and bias of the former situation is about 7.6TECu when that of latter is about 4.9TECu.

2011年8月在新疆天文台南山观测站首次进行了GPS与VLBI空间大地测量技术并置站的本地连接测量。针对南山并置站,本文在建立、优化南山GPS控制网的基础上,探讨本地连接测量中GPS数据处理的方法、精度。通过对GPS控制网7 d连续观测和基于IGS精密星历的GAMIT基线处理、三维空间平差,结果表明:基线在N、E和长度方向的重复性在0.3~0.4 mm,U方向分量重复性为1.4 mm,基线相对精度为0.8×10-8,达到《全球定位系统(GPS)测量规范》(GB/T 18314—2009)中A级网的精度要求,GPS控制点在ITRF2008系统下的坐标精度均优于0.5 mm。

The tropospheric delay is an important error source for the satellite navigation and positioning, and the numerical forecast data derived from meteorological instruments can be used to calculate the tropospheric delay. In this study, the zenith tropospheric delay (ZTD) observed from 49 Global Positioning System (GPS) sites distributed in Asian area is used to assess the effectiveness and accuracy of ZTD calculated with the data from the European Center for Medium-Range Weather Forecasts (ECMWF) and the United States National Centers for Environmental Prediction (NCEP). The practicability of ECMWF/NCEP data in Asian area and the relation between the resolution and the accuracy for the ECMWF data are also studied. The results are: (1) relative to GPS observed ZTD (GPS ZTD), the bias and rms for the ECMWF data are -1.0 cm and 2.7 cm respectively, which are better than that for the NCEP data and can be used for ZTD study and application with high accuracy; the bias and rms for the NCEP forecast data are 2.4 cm and 6.8 cm, which are sufficient for the tropospheric delay correction in the real-time GNSS navigation and positioning. (2) The bias and rms show a seasonal variation, which generally show larger values in summer months and smaller values in winter months; however, the relation between the bias and rms and the latitude is not obvious, but the rms decreases with increasing altitude. In addition, the daily bias and rms at eastern Asian area in summer and at southern in winter have a relatively larger variation. (3) The resolutions of 2.5 degree and 0.5 degree ECMWF data are compared; the rms for the latter is decreased by 1 similar to 5 mm than the former. These results provide a reference for the effectiveness and accuracy of the ECMWF/NCEP data used for calculating the tropospheric delay in the space geodesy, navigation and positioning, and INSAR, etc.

According to the requirement of high-precision satellite navigation, we have introduced the method for the quasi-realtime monitoring of variations of the regional ionospheric total electron content (TEC) and GPS satellite differential code bias (DCB), based on the dual-frequency carrier-phase smoothed pseudorange data obtained from a regional GPS network in China. Especially, we have studied the feasibility of retrieving DCB independently from the regional GPS networks with different sizes. For this purpose, 3 regional networks based on the countrywide GPS stations are investigated. The comparisons of the computed DCB and VTEC(vertical total electron content) with those of CODE(the Center for Orbit Determination in Europe) indicate that in order to realize a reliable quasi-realtime measurement of DCB by a regional network, there is a certain requirement on the size of the regional network, and that the relative accuracies of the quasi-realtime VTEC and DCB measured by using a Chinese GPS regional network can reach 2.0TECu and 0.25ns, respectively.