利用验潮站资料的中国近岸海潮模型精度评估

针对全球海潮模型在我国近海海域精度较差的问题,该文采用中国沿岸30个长期验潮站的调和常数,对比了3种全球海潮模型DTU10、TPXO7.2、NAO.99b和1个区域海潮模型NAO.99Jb在中国沿岸的准确度。通过海潮模型与验潮站分潮的振幅中误差、迟角中误差以及8个主要分潮的预报误差,对渤海、黄海、东海和南海北部进行了详细的分析。结果表明,NAO.99Jb在中国海域精度最高,NAO.99b次之。在渤海海域,DTU10在Q_1分潮精度最高,NAO.99b在K2分潮精度最高,其余分潮均是NAO.99Jb精度最高;在黄海海域,NAO.99b在Q_1分潮精度最高,其余分潮均是NAO.99Jb精度最高;在东海海域,DTU10在Q_1分潮精度最高,TPXO7.2在P1精度最高,NAO.99Jb在O1、M2分潮精度最高,其余分潮均是NAO.99b精度最高;在南海北部海域,DTU10在N2、S2分潮精度最高,其余分潮均是NAO.99Jb精度最高。     

利用改进的动态PPP技术建立中国香港区域海潮负荷位移模型

利用GPS技术反演海潮负荷信息，相比传统重力及甚长基线干涉测量，有着全球覆盖、测站数多、全天候、成本低等诸多优势，为海潮模型的建立提供了有效的技术手段，也对海潮负荷效应的研究有着重要的理论意义和参考价值。利用动态精密单点定位技术（precise point positioning，PPP）反演海潮负荷位移，同时构建了区域海潮负荷位移模型。利用香港连续运行参考站8 a的GPS观测数据，精密测定了11个测站的三维海潮负荷位移参数，与高精度海潮模型提供的海潮负荷位移参数进行比较，发现除K₂、K₁潮波外，其他潮波的均方根误差均小于2 mm。与已有的动态PPP及静态PPP结果对比发现，采用改进的重叠时段动态PPP算法可有效改善K₁潮波的反演精度；该方法反演的海潮负荷位移精度可达到静态PPP反演海潮负荷位移的精度，且对于K₁潮波，在东西方向，动态PPP算法的反演精度较静态PPP略有改善。利用最小二乘曲面拟合法可有效建立中国香港地区GPS区域海潮负荷位移模型，可有效弥补沿海地区因验潮站稀少而导致的海潮模型适应性差的问题。     

利用GPS动态PPP技术求解海潮负荷位移

受特殊海岸线及复杂海底地形的影响,目前发布的全球海潮模型在局部沿海地区差异较大,需利用其他大地测量手段直接测定沿海地区的海潮负荷位移参数。GPS技术因具有全天候、精度高、成本低等优势,已成为获取海潮负荷位移参数的有效手段。本文基于GPS技术监测测站三维位移变化的灵敏度高于监测48个海潮参数的灵敏度这一基本思想,改进了利用GPS精密单点定位(PPP)技术估计48个海潮调和参数的方法,直接逐历元求解三维海潮负荷位移变化,再利用调和分析方法提取主要潮波(M2、S2、N2、K2、K1、O1、P1、Q1)的海潮负荷位移建模参数(振幅与相位)。利用12个香港连续运行参考站(CORS)8年的GPS观测数据,计算各测站的海潮负荷位移建模参数。与传统方法比较,本文方法可有效加速K1潮波在东西方向的收敛。将GPS海潮负荷位移建模参数估值与中国近海海潮模型值比较,发现除S2、K2和K1潮波的均方根误差较大外,其他潮波的均方根误差均小于1.5mm。将香港2008—2014年验潮站数据反演的潮波参数与海潮模型值比较,结果表明:GPS与验潮站数据反演的潮波参数均与中国近海海潮模型及HAMTIDE2011.11A全球海潮模型符合较好,验证了GPS PPP反演海潮负荷位移的有效性。采用GPS PPP估计的8个潮波的振幅与相位值替换全球海潮模型中对应的潮波值,进行海潮负荷效应改正,可减弱GPS长时间序列中的半周年信号。     

不同海潮模型对闽海潮负荷位移估计的影响

针对新型海潮模型对区域海潮负荷位移估计的影响分析不足的问题,该文依托福建省基础地理信息中心A级GNSS网,基于八大系列全球海潮模型的最新版本和区域海潮模型NAO99Jb,分析了不同海潮模型对福建地区海潮负荷位移的影响,并利用验潮站数据评定了海潮模型在当地的适用性.结果表明,海潮模型的差异主要集中在台湾海峡两岸,而在湄洲湾以北至浙江沿海一带,M2分潮的STD甚至超过30 cm;海潮模型差异主要影响海潮负荷位移的垂向分量,平均影响程度基本是水平分量的3倍;福建地区M2、S2、N2、K1和O1等分潮负荷位移的最大差异可达亚毫米至毫米级,且各分潮负荷位移的STD随着离海距离增大按负指数函数规律减小,海潮模型差异仅对近海50 km内的地区影响较大;FES2014b在闽台附近海域精度最高,是福建地区海潮负荷位移估计首选的海潮模型.     

不同海潮模型对东南极沿海地区GPS基线解算的影响

在高精度GPS数据处理中,海潮的影响是一个不可忽略的因素。利用GAMIT软件解算2011年东南极沿海地区中国中山站及其周边6个IGS站的GPS数据,对比分析了FES2004、DTU10、EOT11a、GOT4.7、HAMTIDE11a、OSU12以及TPXO7.2等7个全球海潮模型在不同测站的海潮负荷差异,比较了海潮负荷对于GPS基线解的影响。结果表明,海潮负荷对GPS基线解的影响与测站所处位置及基线方位有关,达到cm级,相对影响达到10-8,因此,在高精度的GPS基线解算中必须考虑海潮的影响;但选用不同海潮模型对东南极沿海地区GPS基线解算的差异可忽略不计。     

南极中山站的重力和区域海洋潮汐特征

本文利用中山站弹簧重力仪记录的重力潮汐时间序列、验潮站数据、CATS2008区域和Eot11a全球海潮模型研究重力和海洋潮汐特征。结果表明,在周日频段,潮波O1的海潮振幅达到28 cm,4个主要潮波（Q1、O1、P1和K1）的全球模型与验潮站潮高差之和为4.2 cm,区域模型与验潮站潮高差之和为4.4 cm;在半日频段,潮波M2的海潮振幅达到20 cm,4个主要潮波（N2、M2、S2和K2）的潮高差之和分别为7.7 cm和5.1 cm,说明利用区域模型修正全球模型的重要性。经区域模型修正的全球海潮负荷改正后,重力主波K1、M2和S2的最终残差振幅分别下降了9.84%、56.14%和37.08%,说明区域海潮模型更能反映海洋潮汐的真实特征,用区域模型修正全球海潮模型的有效性得到验证。     

山东地区GPS测量中的海潮负荷影响

针对影响山东地区GPS测量精度的重要因素之一——海潮负荷,不同海潮模型在山东沿海地区差异较大的问题,该文以山东CORS数据为例,基于FES2004、NAO99b、CSR4.0、GOT00.2 4种全球海潮模型,使用GAMIT软件,分析了海潮负荷对山东地区GPS定位及基线解算的影响。通过对比分析,海潮负荷对山东地区GPS定位的影响主要体现在U方向上,振幅达到厘米级;海潮负荷对山东沿海定位的影响大于山东内陆,U方向达到了2cm,为内陆地区2倍以上;海潮负荷对基线解算的影响与基线方位和基线两端测站负荷差异有关,其中差异较大的基线U方向的影响接近8mm;除GOT00.2海潮模型以外,不同模型对山东地区较长观测时段的GPS数据解算结果的影响并无太大差异,但对于短时观测或实时的GPS高精度定位,半日分潮迟角的精度还有待提高,因此有必要精细化山东区域海潮模型。     

近海潮汐效应对上海地区精密定位的影响

针对全球海潮模型在不同沿海地区存在差异性以及在中国近海精度不高的问题,利用全球海潮模型FES2004和NAO99b计算上海地区(经纬度范围为120.85°E～122.2°E,30.6667°N～31.8833°N)S₂、M₂、K₁和O₁四个分潮的海潮负荷位移在垂直分量上的差异;并利用中国近海模型osu.chinasea.2010对全球海潮模型FES2004中相应的区域进行替换,计算近海效应对SHJZ站(上海金山)、SHJBS站(上海宝山)、SHAO站(上海佘山)以及DCMD站(上海崇明)四个测站精密定位的影响。结果表明:1) 全球海潮模型FES2004和NAO99b在上海地区存在较明显的差异,尤其是垂直分量,最大接近4 mm,且两个模型的差异随离海洋距离增大而减小;2) 利用修正前后的全球海潮模型FES2004经过计算分析得出,近海效应对上海地区GPS测站精密定位的影响达到5 mm,对测站垂直分量的位移影响从大到小分别是DCMD站(5.1 mm)、SHBS站(4.9 mm)、SHJS(4.2 mm)、SHAO(3.6 mm)。      

利用全球海潮模型确定海图深度基准面

比较并分析了FES99潮汐模型和NAO.99Jb潮汐模型在浙江近海的精度;利用调和分析法计算了浙江近海的8个主要分潮和3个浅水分潮的调和常数;研究了浙江近海海图深度基准面的计算方法;利用长期验潮站资料验证了本文方法的可靠性与准确性;利用径向基函数方法格网化了经验潮站海图深度基准值加密后的数据,最终得到了浙江近海分辨率为2.5'×2.5'的海图深度基准面模型.     

佘山台倾斜固体潮观测的海潮负荷改正

采用FARRELL的负荷理论以及最新的TPXO6海潮模型和中国近海潮汐资料计算了海潮负荷对佘山台倾斜固体潮的影响,采用BAYTAP-G调和分析软件对佘山台倾斜固体潮观测进行了处理,获得不同潮波的潮汐参数。在此基础上进行海潮负荷改正。负荷改正后,东西分量的振幅因子和相位滞后与理论值较为接近,而南北分量的半日波振幅因子与理论值仍有较大的偏离。结果说明,佘山台倾斜东西分量主要受海潮负荷的影响,超过60%,甚至达到96%(O1);而南北分量受到的非潮汐的影响要比东西分量受到的影响大,如N2波甚至高达70%,但是这也可能是和海潮模型在近海的不精确有关。     

Ocean tide loading (OTL) displacements from global and local grids: comparisons to GPS estimates over the shelf of Brittany, France

In this paper we examine OTL displacements detected by GPS stations of a dedicated campaign and validate ocean tide models. Our area of study is the continental shelf of Brittany and Cotentin in France. Brittany is one of the few places in the world where tides provoke loading displacements of ∼10–12 cm vertically and a few cm horizontally. Ocean tide models suffer from important discrepancies in this region. Seven global and regional ocean tide models were tested: FES2004 corrected for K2, TPXO.7.0, TPXO.6.2, GOT00.2, CSR4.0, NAO.99b and the most recent regional grids of the North East Atlantic (NEA2004). These gridded amplitudes and phases of ocean tides were convolved in order to get the predicted OTL displacements using two different algorithms. Data over a period of 3.5 months of 8 GPS campaign stations located on the north coast of Brittany are used, in order to evaluate the geographical distribution of the OTL effect. We have modified and implemented new algorithms in our GPS software, GINS 7.1. GPS OTL constituents are estimated based on 1-day batch solutions. We compare the observed GPS OTL constituents of M₂, S₂, N₂ and K₁ waves with the selected ocean tide models on global and regional grids. Large phase-lag and amplitude discrepancies over 20° and 1.5 cm in the vertical direction in the semi-diurnal band of M₂ between predictions and GPS/models are detected in the Bay of Mont St-Michel. From a least squares spectral analysis of the GPS time-series, significant harmonic peaks in the integer multiples of the orbital periods of the GPS satellites are observed, indicating the existence of multipath effects in the GPS OTL constituents. The GPS OTL observations agree best with FES2004, NEA2004, GOT00.2 and CSR4.0 tide models.     

Estimates of ocean tide loading displacements and its impact on position time series in Hong Kong using a dense continuous GPS network

Three-dimensional ocean tide loading (OTL) displacements of eight diurnal and semidiurnal constituents at 12 sites in Hong Kong were estimated using 3–7 years of continuous global positioning system (GPS) observations. OTL displacements were estimated using the precise point positioning (PPP) technique on a daily basis and then combined. The OTL displacements obtained by GPS were compared with predictions using seven recent global ocean tide models. The effect of OTL displacements on GPS position time series was also investigated. The study shows that the GPS-derived OTL displacements (excluding K1 and K2 constituents) agree best with those predicted by the GOT4.7 and NAO99b models. The GPS/model agreement is generally at the sub-millimeter level, except for S2, K1, and K2 constituents with relatively large errors. After systematic biases between the GPS and model values are removed, the misfits of all sites for M2, S2, N2, O1, P1, and Q1 are less than 0.5 and 1.0 mm in the horizontal and vertical components, respectively, while larger misfits (within 2.5 mm) are observed for K1 and K2. Integer ambiguity fixing slightly improves the east component of OTL displacement estimates. The study also finds that GPS-derived OTL corrections, instead of model predicts, can be used in daily data processing with the exception of K1 and K2. Including K2 corrections, a secular vertical rate of up to 1 mm/year in position time series can be induced, which needs to be confirmed by further studies.     

Validating ocean tide loading models using GPS

Ocean tides cause periodic deformations of the Earths surface, also referred to as ocean tide loading (OTL). Tide-induced displacements of the Earths crust relying on OTL models are usually taken into account in GPS (Global Positioning System) data analyses. On the other hand, it is also possible to validate OTL models using GPS analyses. The following simple approach is used to validate OTL models. Based on a particular model, instantaneous corrections of the site coordinates due to OTL are computed. Site-specific scale factors, f, for these corrections are estimated in a standard least-squares adjustment process of GPS observations together with other relevant parameters. A resulting value of f close to unity indicates a good agreement of the model with the actual site displacements. Such scale factors are computed for about 140 globally distributed IGS (International GPS Service) tracking sites. Three OTL models derived from the ocean tide models FES95.2.1, FES99, and GOT00.2 are analyzed. As expected, the most reliable factors are estimated for sites with a large loading effect. In general, the scaling factors have a value close to unity and no significant differences between the three ocean tide models could be observed. It is found that the validation approach is easy to apply. Without requiring much additional effort for a global and self-consistent GPS data analysis, it allows detection of general model misfits on the basis of a large number of globally distributed sites. For detailed validation studies on OTL models, the simultaneous estimation of amplitudes and phases for the main contributing partial tides within a GPS parameter adjustment process would provide more detailed answers.     

A comparison of GPS, VLBI and model estimates of ocean tide loading displacements

In recent years, ocean tide loading displacements (OTLD) have been measured using the Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI). This study assesses the accuracy of GPS measurements of OTLD by comparison with VLBI measurements and estimates derived from numerical ocean tide models. A daily precise point positioning (PPP) analysis was carried out on ∼11 years of GPS data for each of 25 sites that have previous OTLD estimates based on data from co-located VLBI sites. Ambiguities were fixed to integer values where possible. The resulting daily estimates of OTLD, at eight principal diurnal and semi-diurnal tidal frequencies, were combined to give GPS measurements of OTLD at each site. The 3D GPS and VLBI measurements of OTLD were compared with estimates computed (by convolution with Green’s functions) from five modern ocean tide models (CSR4.0, FES2004, GOT00.2, NAO99b and TPXO6.2). The GPS/model agreement is shown to be similar to the VLBI/model agreement. In the important radial direction, the GPS/model misfit is shown to be smaller than the VLBI/model misfit for seven of the eight tidal constituents; the exception being the K2 constituent. Fixing of GPS carrier-phase ambiguities to integer values resulted in a marginal improvement to the GPS/model agreement. Statistically, it is shown there is no significance to the difference between the fit of the GPS and VLBI measurements of OTLD to modelled values. Equally, differences in fit of either the complete set of GPS or VLBI estimates to the five sets of model-derived values cannot be identified with statistical significance. It is thus concluded that, overall, we cannot distinguish between GPS and VLBI measurements of OTLD, and that at the global scale, present ocean tide models are accurate to within the current measurement noise of these techniques.     

GPS精密定位中的海潮位移改正

根据海洋负荷潮理论，利用NAO99b全球海潮模型，计算了中国部分IGS站的海潮位移改正，并将海潮位移改正应用到GPS数据处理当中。在GAMIT软件的解算过程中，分别按加入和不加入海潮位移改正，对GPS基线分量和测站坐标分别进行了计算和比较分析。结果表明，海潮位移改正无论是对GPS基线分量还是对测站坐标，都有一定的影响。     

The gravitational effect of ocean tide loading at high latitude coastal stations in Norway

Gravity measurements close to the ocean are strongly affected by ocean tide loading (OTL). The gravitational OTL effect consists of three parts, i.e. a change in gravity caused by direct attraction from the variable water-masses, by displacement of the observing point due to the load, and by redistribution of masses due to crustal deformation. We compare the OTL gravitational effect of several global models to observed time-series of gravity to identify the best model for four arctic observation sites. We also investigate if the global models are sufficient for correcting gravity observations. The NAO99b model fits the observations best at three stations. At two stations (Tromsø and Bodø) the global models explain the variability in the observations well. At the other two (Honningsvåg and Andøya), a significant periodic signal remains after the OTL correction has been applied. We separate two of the gravitational effects, the direct attraction and the change in gravity due to displacement, to study the local effects. Simple geometric models of the water load and independent measurements from local tide-gauges are used to calculate these effects. This leads to improved correspondence with the OTL signal, hence demonstrating the importance of careful modelling of local effects for correction of gravity observations in coastal stations.