Accuracy assessment of global vertical displacement loading tide models for the equatorial and Indian Ocean

The three-dimensional displacements caused by ocean loading effects are significant enough to impact spatial geodetic measurements on sub-daily or longer timescales,particularly in the vertical direction.Currently,most tide models incorporate the distribution of vertical displacement loading tides;however,their accuracy has not been assessed for the equatorial and Indian Ocean regions.Global Positioning System(GPS)observations provide high-precision data on sea-level changes,enabling the assessment of the accuracy and reliability of vertical displacement tide models.However,because the tidal period of the K_(2) constituent is almost identical to the orbital period of GPS constellations,the estimation of the K_(2) tidal constituent from GPS observations is not satisfactory.In this study,the principle of smoothness is employed to correct the systematic error in K_(2) estimates in GPS observations through quadratic fitting.Using the adjusted harmonic constants from 31 GPS stations for the equatorial and Indian Ocean,the accuracy of eight major constituents from five global vertical displacement tide models(FES2014,EOT11a,GOT4.10c,GOT4.8,and NAO.99b)is evaluated for the equatorial and Indian Ocean.The results indicate that the EOT11a and FES2014 models exhibit higher accuracy in the vertical displacement tide models for the equatorial and Indian Ocean,with root sum squares errors of 2.29 mm and 2.34 mm,res-pectively.Furthermore,a brief analysis of the vertical displacement tide distribution characteristics of the eight major constituents for the equatorial and Indian Ocean was conducted using the EOT11a model.

Ocean tide loading correction for InSAR measurements: Comparison of different ocean tide models

With the rapid development of modern Interferometric Synthetic Aperture Radar(InSAR)missions,SAR instruments with wider coverage can be used to monitor the ground surface deformation from regional to global scale.However,the ocean tide loading(OTL)displacement is becoming a primary source of errors.It contributes to a long-wavelength signal in InSAR interferograms,leading to errors from millimeter to centimeter-level in InSAR deformation monitoring,especially over coastal areas.Although the state-of-the-art has applied ocean tide models to mitigate the errors,the difference between them and their impact on InSAR measurements are rarely discussed.In this paper,we compare representative ocean tide models and investigate their effects in the correction of OTL errors.We found that(i)the modeled OTL displacements from different models show little difference over interiors far from the ocean,while disagreement becomes larger over coastal areas;(ii)the magnitude of OTL artifacts may be greater than the atmospheric delays in some coastal areas,and the correction using ocean tide models can effectively attenuate the OTL effects for large-scale InSAR measurements;(iii)when correcting the OTL errors for InSAR measurements,the global model TPXO and FES are recommended because of their better overall performance,while the NAO model performs the worst.The local models with high spatial resolution can help improve the capability of coarse global models in complex topographic areas.

Ocean Loading Tides Corrections of GPS Stations in Antarctica

This paper describes the ocean loading tides corrections of GPS stations in Antarctica, such as the Great Wall station and Zhongshan station. Based on the theory of ocean loading tides, the displacement corrections of ocean loading tides on GPS stations in Antarctica are calculated by using the CRS4.0 ocean loading tides model. These corrections are also applied to GPS data proc-essing. The GPS data are analyzed by the GAMIT software with and without these corrections. We compared and analyzed the GPS baseline components to get the differences. The results show that the ocean tidal displacement corrections have obvious effects upon GPS baseline components. Therefore, we should not ignore the ocean loading tides corrections of GPS stations in Antarctica to obtain precise and reliable results.

Influence of the modified global ocean tide model with local tides of East and South China Seas on load gravity in China and its neighbor area

By using 11 global ocean tide models and tidal gauge data obtained in the East China Sea and South China Sea, the influence of the ocean loading on gravity field in China and its neighbor area is calculated in this paper. Furthermore, the differences between the results from original global models and modified models with local tides are discussed based on above calculation. The comparison shows that the differences at the position near the sea are so large that the local tides must be taken into account in the calculation. When the global ocean tide models of CSR4.0, FES02, GOT00, NAO99 and ORI96 are chosen, the local effect for M2 is less than 0.10 × 10-8 m·s-2 over the area far away from sea. And the local effect for O1 is less than 0.05 × 10-8 m·s-2 over that area when choosing AG95 or CSR3.0 models. This numerical result demonstrates that the choice of model is a complex problem because of the inconsistent accuracy of the models over the areas of East and South China Seas.

Evaluation of global ocean tide models based on tidal gravity observations in China

Previous studies show that the calculated loading effects from global ocean tide models do not match actual measurements of gravity attraction and loading effects in Southeast Asia.In this paper,taking advantage of a unique network of gravity tidal stations all over the Chinese mainland,we compare the observed and modeled tidal loading effects on the basis of the most recent global ocean tide models.The results show that the average efficiencies of the ocean tidal loading correction for O_(1),K_(1),M_(2) are 77%,7 s3%and 59%,respectively.The loading correction efficiencies using recent ocean tidal models are better than the 40 years old Schwiderskis model at coastal stations,but relative worse at stations far from ocean.

宜昌台超导重力观测中的海潮与大气负荷效应研究

基于2017年宜昌地震台超导重力仪观测数据,对数据预处理、极移改正和长周期趋势改正后的重力潮汐观测数据进行调和分析,获得宜昌台精确地方重力潮汐参数,选取NAO.99b和osu.Chinasea.2010海潮模型研究海潮负荷对重力观测的影响。结果表明,宜昌台海潮负荷变幅约为25 nm·s^(-2),经海潮改正后潮汐因子有所改善。采用时域导纳方法以及基于全球大气模型ERA-Interim计算宜昌台大气重力负荷效应,研究结果表明,宜昌台大气重力导纳值为-3.2193 nm·s^(-2)·hPa^(-1),近区大气重力负荷变幅约为160 nm·s^(-2),远区大气重力负荷变幅可达70 nm·s^(-2),在进行超导重力数据处理分析时全球大气负荷效应不能忽略。

潮汐效应对沿海多条带时序InSAR地表形变监测的影响

潮汐效应对沿海大范围、高精度的合成孔径雷达干涉测量(Interferometric Synthetic Aperture Radar,InSAR)技术地表形变监测的影响不可忽略.潮汐效应中的固体潮(Solid Earth Tide,SET)位移和海洋潮汐负荷(Ocean Tide Loading,OTL)位移会在时间和空间域上对沿海大范围InSAR地表形变监测产生分米级的误差,而且不同条带中地表潮汐形变时空差异性会对多条带InSAR影像拼接产生较大误差.本文针对沿海地区多条带InSAR形变时序,重点分析了潮汐效应在不同条带InSAR地表沉降监测中的影响,并采用多种潮汐位移估计方法对多条带地表潮汐形变进行改正.结果表明,研究区域不同条带时序InSAR中地表潮汐形变具有较大的时空差异性,其造成沿海地区相邻条带时序InSAR地表沉降速率差异能达到1~2 cm·a^(-1);通过固体潮模型、海潮负荷模型或GPS参考站网海潮位移改正,能够消除不同条带中地表潮汐形变时空差异性对时序InSAR形变结果拼接产生的空间高阶非线性误差,弥补了传统拼接方法在拟合潮汐位移偏差的不足.在大气延迟误差改正的基础上,时序InSAR形变残差的标准差(Standard Deviation,STD)由潮汐改正前的2.3 cm减少至0.75 cm;本文研究揭示了沿海地表潮汐形变改正对多条带时序InSAR形变结果拼接的重要性,可大幅提高沿海地区广域时序InSAR地表形变监测的精度.

利用GPS观测中国大陆固体地球潮汐形变

利用中国陆态网242个GPS连续观测站超过10年的观测数据,采用精密单点定位静态方法获得了八个主要潮波的三维潮汐位移.与建模值对比结果表明,GPS观测潮汐位移的精度可达亚毫米级.进一步将GPS观测值与OTL(Ocean Tide Loading)建模值对比,除DTU10外其他七种海潮模型与GPS观测值之间一致性较好.综合考虑验潮站观测结果,最适合中国大陆M2、O1潮波OTL建模的海潮模型是TPXO9-Atlas,地球模型为PREM.本研究还发现,M2、O1潮波GPS观测值与建模值之间的残差存在明显的大尺度空间相关性,表明中国地区存在固体潮建模误差等系统误差.本文对198个离海岸线距离超过200 km的内陆站点的系统误差进行分析,改正系统误差后内陆站点东、北和垂直方向加权均方根误差(Weighted Root Mean Square,简称WRMS)分别为:0.04 mm、0.07 mm和0.11 mm(M2),0.05 mm、0.07 mm和0.11 mm(O1);44个沿海站点WRMS分别为:0.18 mm、0.27 mm和0.59 mm(M2),0.10 mm、0.16 mm和0.30 mm(O1).部分沿海站点仍存在较大残差,主要源于海潮负荷位移建模误差,除海潮模型外还包括海水密度、地球模型、上地幔和地壳模型等因素影响.本文首先使用最新WOA(World Ocean Atlas)18海洋数据集计算海水密度和可压缩性的影响,结果表明中国内地OTL建模对海水密度变化和可压缩性并不敏感.其次,软流圈滞弹性散耗效应可使半日潮软流圈的剪切模量降低约8.5%,周日潮软流圈的剪切模量降低约9.1%,考虑滞弹性散耗效应,M2、O1潮波垂直方向上残差最大可分别减小0.50 mm、0.25 mm.最后,本文利用GPS实测数据对四种三维地球模型进行了适用性评价,结果表明除USTC地球模型受沉积层影响外,其他三种地球模型都能有效提高GPS观测结果与理论建模结果的一致性;另外全球地壳模型CRUST1.0与GPS观测值之间的残差最小,说明中国大陆海潮负荷建模精度受地壳结构精度影响较大.本文研究结果证明现今中国大陆GPS观测潮汐位移的结果已经具有足够的精度用于约束该区域地球内部结构.

基于动态精密单点定位技术估计海潮负荷位移

本研究应用动态精密单点定位(PPP)技术,基于香港地区全球导航卫星系统(GNSS)5个测站的垂直坐标时间序列,估计海潮负载位移,并与海潮模型预测进行比较分析。研究中采用奇异谱分析(SSA)对时间序列进行降噪处理,分析噪声对海潮负载位移估计的影响。结果表明,SSA降噪显著提升了坐标时间序列的精度,其中白噪声和有色噪声分别下降了60.4%和21.68%。SSA降噪后,海潮负载位移反演值与模型预测值间的差异减少,显示噪声改正对提升反演精度有积极作用。利用GNSS PPP估计的M_(2)、K_(1)、K_(2)、O_(1)这四种主要潮汐分量引起的地表负载位移,与海潮模型的预测值之间存在一定的偏差,但SSA降噪后的均方根误差不符值有所下降。本研究证实了利用GNSS PPP技术估计海潮负载位移的可行性,并强调了降低噪声在提高估计精度方面的重要性。

高精度重力测量的潮汐改正软件及其评估分析

基于MATLAB GUI界面,采用天顶距直接法和负荷格林函数法编写一套重力固体潮与海洋潮汐负荷改正软件GTIDE,并将其与国际现有软件进行比较。结果表明,GTIDE软件易于操作、便于维护,能有效揭示重力固体潮与海洋潮汐负荷的变化特征,适用于高精度绝对重力与相对重力测量的潮汐改正。

CG型重力仪用于海潮负荷观测的可行性

为验证便携式相对重力仪用于短时重力潮汐观测的可行性,在厦门地震台进行同址对比测试。以利用gPhone重力仪的长观测时段数据修正的FES2004海潮模型为参考,分离出gPhone、CG-5和CG-6型重力仪的静态观测残差序列。结果表明,CG-5和CG-6型重力仪在1 CPD(circle per day)和2 CPD附近的噪声水平(非线性漂移)与gPhone重力仪接近,对主要的全日分潮和半日分潮分析影响较小,观测精度能满足短时海潮模型修正的需要。以CG-5型重力仪在平潭岛的短时重力潮汐数据修正FES2014海潮模型得到测站海潮模型,并回测35 d前绝对重力观测时段的重力海潮负荷值。改正后组均值残差标准差从FES2014模型的2.7μGal降至1.8μGal,由此验证了CG型便携式相对重力仪用于海潮负荷观测的可行性。

Determination of ocean tide loading displacements in Hong Kong using GPS technique

Ocean tide loading (OTL) displacements of eight principal constituents at 12 sites in Hong Kong were determined using more than eight years of continuous GPS observations. Parameters of the OTL displacements were estimated using daily GPS solutions obtained with precise point positioning (PPP) technique. The results were compared with predictions from seven latest global ocean tide models. Gravity measurements of OTL in Hong Kong were also used to validate the GPS results. The study shows that the results from both the GPS and gravity measurements agree best with the GOT4.7 and NAO99b models, when the K1 and K2 constituents are excluded. The agreements between the GPS and the model estimates are generally at sub-millimeter level in both the horizontal and vertical directions, except for S2, K2 and K1 constituents that have relatively larger errors. After removing the systematic biases between the GPS and the model estimates, the misfits of M2, S2, N2, O1, P1 and Q1 at all sites are within 0.5 and 1.0 mm in the horizontal and the vertical directions, respectively, whereas K1 and K2 show relatively larger misfits of up to 2.3 mm. Both the GPS and the gravity S2 estimates have large biases with unknown reasons when compared with the modeled values, which needs to be further investigated. The study demonstrates that GPS is capable of estimating the OTL displacements with the same accuracy as the model predictions, especially for coastal areas.

LOADING CORRECTION OF OCEANIC TIDES IN THE MAINLAND OF CHINA

The response of radial inhomogeneous elastic earth under the action of oceanic tides is studied by use of the combination of convolution integral with spherical harmonic expansion. In the meantime, the effect of oceanic tides on gravity, tilt and strain in the mainland of China is estimated, and the accuracy of loading correction is also briefly analysed. Results show that the loading effect along the coast of China cannot be neglected, for gravity it is about 5％ of body tides, for tilt it reaches the same magnitude as body tides, for strain about 50％. The result obtained can be used to provide the tidal correction for various precision geodesy. The proposal method may also be applied to the effect of other surface loading except oceanic tides.

海潮模型在北斗精密单点定位中的影响分析

针对海潮负荷影响全球卫星导航系统高精度导航定位的问题,借助北斗卫星导航系统(BDS)观测数据,对比分析了海潮模型在北斗二号(BDS-2)、北斗三号(BDS-3)、北斗二号和三号(BDS-2+BDS-3)精密单点定位(PPP)中的影响。结果表明,海潮模型使BDS-2 PPP在N、E和U方向精度分别提升20.18%、20.20%、25.40%,使BDS-3 PPP在N、E和U方向精度分别提升14.81%、14.22%、15.30%,使BDS-2+BDS-3 PPP在N、E和U方向精度分别提升9.13%、9.41%、10.01%。

海潮负荷模型在不同地理区域精度对比分析

针对海潮负荷模型在不同地理区域(海岛、沿海、内陆)对定位精度的影响,本文基于中国大陆构造环境监测网络的监测数据,借助GAMIT/GLOBK 10.7软件使用FES2004、CRS4.0海潮模型分别对数据进行解算,对不同地理区域定位结果进行分析。实验结果表明,海潮负荷模型在高精度GNSS定位数据处理中对海岛地区的测站影响最大,对沿海地区的影响次之,对内陆地区的影响可以忽略不计。FES2004模型和CRS4.0模型对海岛、沿海和内陆解算结果较为一致,在海岛地区N、E方向上的偏差为毫米级,在U方向上的偏差为厘米级,在沿海地区N、E、U方向上的偏差均为毫米级,但U方向上影响程度基本是N、E方向上的3倍左右。

The Analyses of the Tilt Tides and the Loading Effect of Ocean Tides on the Tilt Tides

Using tidal potential solar thermal-radiating energy current and the nonlinear effect of the gravity tide as the input function, moreover, considering the ocean tidal species as the input function of the loading effect of ocean tide, we make the lumped response analysis of the observational tilt tide in one year. The tilt gravitational tide, the load tide, the radiational tide and the nonlinear tide with the same frequeny are separated off. It is shown that the load tide and the gravitational tide are the same quantity grade, the load tide may spread into inland far away; the solar thermal-radiation has an effect on the tilt tide; there is a little nonlinear tide in the tilt tide, but the nonlinear tide of the ocean tide has the stronger loading effect on the tilt tide than the nonlinear tide brought about by the gravitational tide itself; the lag interval, △τ=41 (h), is the best value in the response analysis. In addition, the harmonic analyses of the tilt tide and the separated tilt tides are made respectively by using j.v model, and their ellipse factors are calculated.

佘山地震监测中心站重力固体潮海潮负荷效应分析

佘山地震监测中心站重力固体潮汐观测受海潮负荷影响较大,选取2020年1月-2021年10月重力整点值数据,采用Eterna3.30标准潮汐分析软件获得重力潮汐参数,8个主波振幅因子中误差均在1%以内。选择8个全球海潮模型,对振幅较大的O_(1)、K_(1)和M_(2)波进行海潮负荷改正效应分析。结果表明,O_(1)、K_(1)和M_(2)波的重力海潮负荷振幅分布在4.6-5.4μGal,在经全球海潮模型负荷改正后,周日波O_(1)、K_(1)残差振幅大幅减小,其残差负荷改正平均有效性分别为55.90%和71.27%;而半日波M2振幅未得到有效改正,可能与未考虑区域海潮模型有关。

基于不同海潮模型研究海潮负荷对GPS精密定位的影响

为研究海潮负荷在不同区域对GPS定位影响的规律,推导分析了海潮负荷对GPS测站定位影响的计算公式,并基于此,以江苏、西安区域GPS测站为例,用卫星测高数据反演获得的NAO99b海潮模型及FES2004海潮模型计算了海潮负荷对GPS定位以及对GPS基线的影响,结果表明海潮负荷对GPS沿海测站定位的影响达厘米量级,为内陆地区的4～5倍,而且海潮负荷对测站U方向的影响远大于对E、N方向的影响,海潮负荷对不同区域的GPS基线长度的影响均小于1 cm;结果比较表明NAO99b和FES2004海潮模型在内陆的差异很小,在沿海处差异较大(达1厘米以上)。

绝对重力观测的潮汐改正

讨论了绝对重力观测中的潮汐改正问题 ,重点对绝对重力观测中的海潮负荷影响进行了研究。利用 3个不同地区大潮期间的绝对重力观测结果 ,对目前国际上几个精度较高的海潮模型进行了检验。结果表明 ,用目前国际上几个新的精度较高的海潮模型作海潮负荷影响改正明显好于以往采用的Schwiderski海潮模型。沿海地区大潮期间的绝对重力观测结果经过海潮改正后 ,观测精度虽能得到明显提高 ,但很难达到 2× 10 -8m·s-2 。

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。