一种改进小波阀值算法的变形监测数据滤波方法

针对变形监测数据的去噪问题,在分析现有阀值确定方法的基础上,提出了一种新的小波阈值算法。实际算例表明,新算法能够有效地克服软阈值法存在的恒定偏差,进一步地提高了消噪的精度和可靠性。     

基于精密单点定位技术的航空测量应用实践

讨论了基于精密单点定位技术来实现无地面基准站的航空测量。计算结果表明，用观测值的验后残差计算得到的实测动态及静态模拟动态进行精密单点定位的三维RMS均优于3cm；用动态数据精密单点定位的结果同多基准站的双差解求较差计算出的RMS．南北分量和东西分量均优于5cm，高程分量优于10cm；用基准站的静态数据模拟动态单点定位解算得到的坐标同已知坐标求较差计算出的RMS，南北分量和东西分量均优于3cm，高程分量优于5cm。     

利用卫星红外高光谱资料反演大气甲烷浓度垂直廓线

基于欧洲中尺度天气预报中心(ECMWF)大气廓线库和RTTOV9.3辐射传输正向模式,探讨了大气CH₄混合比浓度垂直廓线和柱总量的经验正交函数(EOF)反演方法,并利用地基傅里叶热红外光谱仪(FTS)观测数据和红外EOSAQUA卫星的大气红外传感器(AIRS)实际观测资料进行反演实验和验证。并且与地基傅里叶热红外光谱仪(FTS)观测结果相比,300hPa以下EOF模型反演的CH₄混合比均方根相对误差小于AIRS的CH₄产品,CH₄柱总量的相对误差也小于AIRS产品。与AIRS的CH₄产品相比,EOF模型反演的CH₄混合比廓线相关系数为0.97,均方根相对误差小于2.5%。验证结果表明EOF模型可以为物理反演提供很好的初始值,由于其稳定且运算更快捷,在业务化运行方面具有很大应用前景。     

GPT2w模型在中国区域的精度检验与分析

全球温度气压湿度（global pressure and temperature 2 wet，GPT2w）模型常被用于计算某一位置的气温、加权平均温度、气压以及水汽压等各种气象参数，是目前公开的标称精度最高的对流层延迟经验模型。利用中国区域参与全球气象交换的86个测站2013-2015年的气象探空数据，对GPT2w得到的各种气象参数进行精度检验及分析。实验结果表明，气温平均偏差为1.31℃，均方根误差为3.62℃；加权平均温度的平均偏差为-1.58 K，均方根误差为4.07 K；气压和水汽压平均偏差的绝对值在1 hPa以内，其均方根误差分别为6.98 hPa与3.04 hPa。利用2006-2015年的数据分析了不同纬度模型精度的周期性特征，结果表明，气温、加权平均温度、气压和水汽压的均方根误差均具有一定的年周期特性，且在不同的纬度区域其周期特性不同。总体而言，GPT2w模型在中国地区范围内具有较高的精度和稳定性。     

利用动态PPP技术确定海潮负荷位移

利用动态PPP对香港12个GPS测站2007—2012年的数据反演了海潮负荷位移,通过与7个全球海潮模型、1个区域模型和静态PPP反演的结果比较发现,相对于另外几个模型,动态PPP反演结果与TPXO.7.2、EOT11a、HAMTIDE和NAO99Jb模型的结果符合得更好。与静态PPP的结果比较发现其RMS与各模型的RMS大体上一致,只是在S2、K2和K1的E方向和M2、S2的N方向稍有增加。此外,除K2和K1潮波外,动态PPP与模型的RMS值在水平方向上均小于1 mm,在垂直方向上均小于2.5 mm,能达到和静态PPP相当的精度。本文反演的结果与NAO99Jb模型值存在明显的系统偏差,当去除系统偏差后,所有潮波的RMS值都有明显的减小,尤其在K1的垂直方向RMS从16.4 mm减少到1.3 mm。此外,通过将香港2012年验潮站数据反演的潮波参数与模型的结果进行比较发现,其结果同样与TPXO.7.2、EOT11a、HAMTIDE和NAO99Jb这4个模型更为符合,这进一步验证了动态PPP反演海潮的有效性,同时说明这4个模型比较适合香港区域。     

Initial results of precise orbit and clock determination for COMPASS navigation satellite system

The development of the COMPASS satellite system is introduced, and the regional tracking network and data availability are described. The precise orbit determination strategy of COMPASS satellites is presented. Data of June 2012 are processed. The obtained orbits are evaluated by analysis of post-fit residuals, orbit overlap comparison and SLR (satellite laser ranging) validation. The RMS (root mean square) values of post-fit residuals for one month’s data are smaller than 2.0 cm for ionosphere-free phase measurements and 2.6 m for ionosphere-free code observations. The 48-h orbit overlap comparison shows that the RMS values of differences in the radial component are much smaller than 10 cm and those of the cross-track component are smaller than 20 cm. The SLR validation shows that the overall RMS of observed minus computed residuals is 68.5 cm for G01 and 10.8 cm for I03. The static and kinematic PPP solutions are produced to further evaluate the accuracy of COMPASS orbit and clock products. The static daily COMPASS PPP solutions achieve an accuracy of better than 1 cm in horizontal and 3 cm in vertical. The accuracy of the COMPASS kinematic PPP solutions is within 1–2 cm in the horizontal and 4–7 cm in the vertical. In addition, we find that the COMPASS kinematic solutions are generally better than the GPS ones for the selected location. Furthermore, the COMPASS/GPS combinations significantly improve the accuracy of GPS only PPP solutions. The RMS values are basically smaller than 1 cm in the horizontal components and 3–4 cm in the vertical component.     

基于RPC模型的线阵卫星影像核线排列及其几何关系重建

针对核线影像无几何模型的问题,提出基于有理多项式系数(Rational Polynomial Coefficient,RPC)模型,利用投影轨迹法制作线阵推扫式卫星核线影像及其几何模型的重建方法。利用SPOT 5 HRG、CBERS 2-03异轨立体像对和SPOT 5 HRSI、RS P5、GeoEyeI、KONOS同轨立体像对重建的核线影像几何模型上下视差的中误差在0.2个像元之内;利用重建几何模型和原始影像几何模型进行前方交会计算所得到的地面点平面中误差在1 m之内,高程中误差在0.3 m之内,验证了本文方法的可靠性。     

一种优化的对流层天顶延迟融合模型FZTD

对流层延迟是影响全球卫星导航系统(GNSS)定位精度的主要误差源之一,模型修正法是目前削弱对流层延迟影响的主要方法. 以简单易用的角度为切入点,综合UNB3模型的简易性和GPT2w模型的高精度特点,构建一种简易且精度较高的对流层天顶延迟融合模型(FZTD). 并利用多年的国际GNSS服务(IGS) 对流层天顶延迟(ZTD)数据对该模型精度进行了验证. 结果表明FZTD模型的均方根(RMS)与平均偏差(bias)值分别为4.4 cm和?0.3 cm,均小于传统模型UNB3m(RMS:5.1 cm,bias:1.1 cm)和EGNOS(RMS:5.1 cm,bias:0.3 cm),定位精度提高了14%,而且在南半球提高尤为明显,特别在南极地区,精度提高了近3倍,弥补了传统模型在南北半球精度差异大的不足. 新模型总气象参数仅为120个比GPT2w模型急剧减少,与传统模型相当,为GNSS实时导航定位终端的预定义对流层延迟改正提供了更优的选择.      

亚洲地区EGNOS天顶对流层延迟模型单站修正与精度分析

以亚洲地区46个IGS站2008-2011年实测的高精度天顶对流层延迟（ZTD）数据为参考值,通过对2008-2010年EGNOS模型计算ZTD的日均偏差进行频谱分析,建立了亚洲地区EGNOS模型的单站修正模型（SSIEGNOS）,对EGNOS和SSIEGNOS模型在亚洲地区的精度和适用情况进行了评估,结果表明：（1）EGNOS模型偏差和RMS在时间分布上呈现明显的季节变化规律,而SSIEGNOS模型偏差和RMS变化较小且平稳;（2）在空间分布上,两种模型的偏差随着经纬度和高程的变化均无明显规律,但随着高程或者纬度的增加RMS总体上都有递减的趋势;（3）SSIEGNOS模型预测ZTD的精度相对于EGNOS模型有明显提高。     

IGS RTS钟差数据中断的实时修复方法研究

针对IGS RTS实时数据流产品在网络传输过程中普遍存在的数据中断问题,基于卫星钟差预报算法,文中提出实时“预报修复”方法,以钟差预报值实时修复发生中断历元的钟差数据。通过对RTS数据中断区间分布的统计分析,确定钟差预报的时间长度为5 min;采用改进的灰色系统模型,对不同时间长度初始数据的钟差预报结果进行对比,确定初始数据时间长度为10 min。以IGS事后精密卫星钟差产品为参考,对连续7 d RTS钟差产品的实时预报修复效果进行验证。以IGS02产品为例,连续7 d预报修复钟差值的平均RMS优于0.17 ns,预报修复后24 h钟差产品的RMS均在0.22 ns以内。     

基于球冠谐分析的区域精密对流层建模

对流层延迟是影响GPS定位精度的主要误差来源。随着精度要求的提高,经验模型已经不能满足精密定位的需要,而世界许多地区建立的连续运行参考站系统为建立区域对流层模型提供了一个很好的契机。本文分析了常用的对流层区域实时模型方法的不足,提出了基于球冠谐 (SCHA, Spherical Cap Harmonic Analysis)的区域精密对流层模型。与常用的四参数模型进行对比分析发现,SCHA模型在内符合精度上有显著提高（RMS值在5mm内）,在外符合精度上比传统模型拟合效果提高了50%左右（RMS值在1cm内）。SCHA模型能更好的描述对流层的空间变化,适用于大区域对流层延迟实时建模。     

Real-Time Precise Point Positioning (RTPPP) with raw observations and its application in real-time regional ionospheric VTEC modeling

Precise Point Positioning (PPP) is an absolute positioning technology mainly used in post data processing. With the continuously increasing demand for real-time high-precision applications in positioning, timing, retrieval of atmospheric parameters, etc., Real-Time PPP (RTPPP) and its applications have drawn more and more research attention in recent years. This study focuses on the models, algorithms and ionospheric applications of RTPPP on the basis of raw observations, in which high-precision slant ionospheric delays are estimated among others in real time. For this purpose, a robust processing strategy for multi-station RTPPP with raw observations has been proposed and realized, in which real-time data streams and State-Space-Representative (SSR) satellite orbit and clock corrections are used. With the RTPPP-derived slant ionospheric delays from a regional network, a real-time regional ionospheric Vertical Total Electron Content (VTEC) modeling method is proposed based on Adjusted Spherical Harmonic Functions and a Moving-Window Filter. SSR satellite orbit and clock corrections from different IGS analysis centers are evaluated. Ten globally distributed real-time stations are used to evaluate the positioning performances of the proposed RTPPP algorithms in both static and kinematic modes. RMS values of positioning errors in static/kinematic mode are 5.2/15.5, 4.7/17.4 and 12.8/46.6 mm, for north, east and up components, respectively. Real-time slant ionospheric delays from RTPPP are compared with those from the traditional Carrier-to-Code Leveling (CCL) method, in terms of function model, formal precision and between-receiver differences of short baseline. Results show that slant ionospheric delays from RTPPP are more precise and have a much better convergence performance than those from the CCL method in real-time processing. 30 real-time stations from the Asia-Pacific Reference Frame network are used to model the ionospheric VTECs over Australia in real time, with slant ionospheric delays from both RTPPP and CCL methods for comparison. RMS of the VTEC differences between RTPPP/CCL method and CODE final products is 0.91/1.09 TECU, and RMS of the VTEC differences between RTPPP and CCL methods is 0.67 TECU. Slant Total Electron Contents retrieved from different VTEC models are also validated with epoch-differenced Geometry-Free combinations of dual-frequency phase observations, and mean RMS values are 2.14, 2.33 and 2.07 TECU for RTPPP method, CCL method and CODE final products, respectively. This shows the superiority of RTPPP-derived slant ionospheric delays in real-time ionospheric VTEC modeling.     

Numerical prediction methods for clock deviation based on two-way satellite time and frequency transfer data

Three functional models, polynomial, spectral analysis, and modified AR model, are studied and compared in fitting and predicting clock deviation based on the data sequence derived from two-way satellite time and frequency transfer. A robust equivalent weight is applied, which controls the significant influence of outlying observations. Some conclusions show that the prediction precision of robust estimation is better than that of LS. The prediction precision calculated from smoothed observations is higher than that calculated from sampling observations. As a count of the obvious period variations in the clock deviation sequence, the predicted values of polynomial model are implausible. The prediction precision of spectral analysis model is very low, but the principal periods can be determined. The prediction RMS of 6-hour extrapolation interval is 1 ns or so, when modified AR model is used.     

基于卫星双向时间频率传递进行钟差预报的方法研究

用多项式拟合、谱分析、改进的AR模型三种方法对由卫星双向时间频率传递得出的钟差时间序列进行了拟舍和预报分析。为了抵制钟差时间序列中异常值的影响，引入了“抗差等价权”，利用卫星双向时间频率传递得到的1d的钟差，按不问采样率、不同时间跨度进行计算分析。结果表明，抗差估计的预报精度明显高于最小二乘估计；平滑值的预报精度高于采样值；由于钟差时间序列中有明显的周期变化，多项式进行钟差预报的精度不可靠；用谱分析进行钟差预报的精度不高，但可以发现钟差时间序列中的主要周期变化；改进的AR模型预报精度最高，预报6h钟差的RMs在1ns左右。     

Combining the orbits of the IGS Analysis Centers

Currently seven Analysis Centers of the International GPS Service for Geodynamics (IGS) are producing daily precise orbits and the corresponding Earth Orientation Parameters (EOP). These individual products are available at several IGS Data Centers (e.g. CDDIS, IGN, SIO, etc.). During 1993 no official IGS orbits were produced, but the routine orbit comparisons by IGS indicated that, after small orientation and scale alignments, the orbit consistency was approaching the 20 cm level (a coordinate RMS), and that some orbit combination should be possible and feasible. An IGS combined orbit could provide a precise and efficient extension of the IERS Terrestrial Reference Frame (ITRF). Another advantage of such a combined orbit would be reliability and precision.Two schemes of orbit combinations are considered here: (a) the first method consists of a weighted averaging process of the earth-fixed satellite positions as produced by the individual Centers; (b) the second method uses the individual IGS orbit files as pseudo-observations in an orbit determination process, where in addition to the initial conditions, different parameter sets may be estimated. Both orbit combination methods have been tested on the January 1993 orbit data sets (GPS weeks 680 and 681) with an impressive agreement at the 5 cm level (coordinate RMS). The quality of the combined orbits is checked by processing a set of continental baselines in two different regions of the globe using different processing softwares. Both types of combined orbits gave similar baseline repeatability of a few ppb in both regions which compared favorably to the best individual orbits in the region.     

An analysis of carrier phase differential kinematic GPS positioning using DynaPos

A series of activities have been carried out at the University of New Brunswick in an effort to evaluate advances in long-range marine kinematic differential positioning. These activities involved processing and analysis of GPS carrier phase kinematic data sets. Some of the data was collected by UNB and some was provided by The XYZs of GPS Inc. Data were collected using Trimble 5700 and Ashtech Z-12 receivers. The data sets were processed using the software DynaPos provided by the The XYZs of GPS Inc. The best results obtained in our analysis indicate an agreement of 5 cm RMS for the horizontal component and 12 cm RMS for the vertical component between two ionospheric-delay free solutions, in baselines varying from 40 to 100 km.     

联合多代测高数据建立中国海域重力异常模型

本文联合T/P数据、T/P新轨道数据、ERS数据、GFO数据、GeosatGM数据和ERS-1/168数据,用测高卫星记录点的位置信息直接计算沿轨大地水准面的方向导数,结合测线轨迹方向的方位角在交叉点处推求垂线偏差,然后利用逆Vening-Meinesz公式计算了中国近海(0o～41oN,105o～132oN)2′×2′格网分辨率的海域重力异常模型。将其与CLS_SHOW99重力异常模型比较,统计结果表示与该模型差异的RMS为8.15mgal,在剔除差值大于20mgal的点(剔除3.3%)以后,RMS为4.72mgal;与某海区船测重力异常比较的RMS为8.91mgal。     

PPP_AR模糊度固定模式下的PPP性能分析

利用6个IGS跟踪站一周的静态数据,采用采样间隔为30 s的卫星钟差产品,对精密单点定位（PPP）整周模糊度的固定模式——PPP_AR模式和常规的浮点解模式下的定位精度和收敛时间进行了比较试验。结果表明,PPP_AR模糊度固定模式下,数据之间具有自洽性,定位精度在E-W和N-S两个方向的RMS都优于1 cm,在U-D方向优于3.5 cm,明显高于浮点解模式下的定位精度。且PPP_AR模式下整周模糊度的固定率都在93％以上。PPP_AR模式下的收敛时间集中在20～25 min,浮点解模式25～35 min。      

Simultaneous estimation of cross-validation errors in least squares collocation applied for statistical testing and evaluation of the noise variance components

The cross-validation technique is a popular method to assess and improve the quality of prediction by least squares collocation (LSC). We present a formula for direct estimation of the vector of cross-validation errors (CVEs) in LSC which is much faster than element-wise CVE computation. We show that a quadratic form of CVEs follows Chi-squared distribution. Furthermore, a posteriori noise variance factor is derived by the quadratic form of CVEs. In order to detect blunders in the observations, estimated standardized CVE is proposed as the test statistic which can be applied when noise variances are known or unknown. We use LSC together with the methods proposed in this research for interpolation of crustal subsidence in the northern coast of the Gulf of Mexico. The results show that after detection and removing outliers, the root mean square (RMS) of CVEs and estimated noise standard deviation are reduced about 51 and 59%, respectively. In addition, RMS of LSC prediction error at data points and RMS of estimated noise of observations are decreased by 39 and 67%, respectively. However, RMS of LSC prediction error on a regular grid of interpolation points covering the area is only reduced about 4% which is a consequence of sparse distribution of data points for this case study. The influence of gross errors on LSC prediction results is also investigated by lower cutoff CVEs. It is indicated that after elimination of outliers, RMS of this type of errors is also reduced by 19.5% for a 5 km radius of vicinity. We propose a method using standardized CVEs for classification of dataset into three groups with presumed different noise variances. The noise variance components for each of the groups are estimated using restricted maximum-likelihood method via Fisher scoring technique. Finally, LSC assessment measures were computed for the estimated heterogeneous noise variance model and compared with those of the homogeneous model. The advantage of the proposed method is the reduction in estimated noise levels for those groups with the fewer number of noisy data points.     

GPS satellite clock determination in case of inter-frequency clock biases for triple-frequency precise point positioning

Significant time-varying inter-frequency clock biases (IFCBs) within GPS observations prevent the application of the legacy L1/L2 ionosphere-free clock products on L5 signals. Conventional approaches overcoming this problem are to estimate L1/L5 ionosphere-free clocks in addition to their L1/L2 counterparts or to compute IFCBs between the L1/L2 and L1/L5 clocks which are later modeled through a harmonic analysis. In contrast, we start from the undifferenced uncombined GNSS model and propose an alternative approach where a second satellite clock parameter dedicated to the L5 signals is estimated along with the legacy L1/L2 clock. In this manner, we do not need to rely on the correlated L1/L2 and L1/L5 ionosphere-free observables which complicates triple-frequency GPS stochastic models, or account for the unfavorable time-varying hardware biases in undifferenced GPS functional models since they can be absorbed by the L5 clocks. An extra advantage over the ionosphere-free model is that external ionosphere constraints can potentially be introduced to improve PPP. With 27 days of triple-frequency GPS data from globally distributed stations, we find that the RMS of the positioning differences between our GPS model and all conventional models is below 1 mm for all east, north and up components, demonstrating the effectiveness of our model in addressing triple-frequency observations and time-varying IFCBs. Moreover, we can combine the L1/L2 and L5 clocks derived from our model to calculate precisely the L1/L5 clocks which in practice only depart from their legacy counterparts by less than 0.006 ns in RMS. Our triple-frequency GPS model proves convenient and efficient in combating time-varying IFCBs and can be generalized to more than three frequency signals for satellite clock determination.