武汉和京都台站超导重力仪高精度潮汐重力观测结果

利用高精度潮汐重力场观测研究地球物理学和地球动力学问题已成为当今地学工作者的共识.由于某些信号十分微弱且具有区域和全球分布特征,相当一部分信号被混合在常规仪器的观测噪声水平上,因此获得全球分布的第一手高精度观测资料显得尤为重要.超导重力仪具有精度高,连续性和稳定性好等特征,期望能在测定区域和全球重力场的精细结构方面发挥重要作用.有18个台站参加的全球地球动力学合作项目于1997年7月份开始实施,其主要目的是解决诸如固体潮、地核近周日晃动、核模、地球自转和极移,地球和大气海洋的耦合机理以及由构造运动引起的重力场变化等热点问题.我们曾研究过中比法三国的超导重力仪潮汐观测资料,获得了欧洲和亚洲不同地区潮汐常数及分布特征.本文将利用武汉和日本京都三台超导重力仪观测资料研究亚洲地区大陆和海岛上的潮汐波振幅因子和相位滞后的时间变化特征以及各参数的误差估计等,同时将检测由大气和海潮变化产生的重力信号.文章分数据处理方法、潮汐参数测定、大气重力信号、海潮重力信号、潮汐参数的时间变化、非潮汐重力场变化特征等几方面叙述.     

利用GNSS数据分析大港验潮站地壳沉降

青岛大港验潮站的地壳沉降关系到该站平均海平面的绝对变化,因而也就关系到我国高程基准面的变化。本文利用青岛GNSS基准站约10年的观测数据对该站的地壳沉降变化进行分析。首先将青岛GNSS基准站纳入由50个国际IGS站和43个国内陆态网络基准站组成的全球网中,进行单日松弛解和单日约束解解算,获得该站坐标时间序列。然后对该站垂向坐标时间序列进行分析,利用粗差探测、偏差探测、趋势项分析、频谱分析等方法对粗差、偏差、趋势项和周期项进行探测、分析,并通过时间序列模型估计获得时间序列中的周期项振幅和偏差估值。分析表明青岛GNSS基准站垂直方向近一段时间未发现存在显著性的地壳沉降变化,但受到比较明显的周年和半周年周期变化影响。结合青岛大港验潮站验潮数据分析结果得出结论:青岛大港验潮站平均海平面的绝对上升速率是1.62mm/a。     

大港验潮站潮汐分析与国家高程基准面变化

利用1980—2011年小时潮位数据和1952—2007年月平均潮位数据,对大港验潮站处海洋潮汐以及国家高程基准面近60年的变化进行了分析和研究。首先利用傅里叶变换对两组数据进行频谱分析,获得了影响海水面变化的180个较短周期分潮以及6个长周期分潮;然后对小时潮汐数据进行最小二乘调和分析,获得影响海水面变化的主要分潮的振幅及其变化,发现Q1、O1、M2、K1、K2的振幅具有非常明显的约19年的周期变化;并利用调和分析和18.61年移动平均对国家高程基准面的变化进行了估算,分别获得基准面1952—1980年的下降速率为1.07mm/a和0.76mm/a,1980—2011年的上升速率为1.59mm/a和1.62mm/a;最后,通过18.61年移动平均对1985高程基准进行了检核,发现两者相差0.14cm。     

Multipath mitigation via component analysis methods for GPS dynamic deformation monitoring

Multipath is one of the main error sources in high-precision global positioning system (GPS) dynamic deformation monitoring, as it is difficult to be mitigated by differencing between observations. In addition, since a specific frequency threshold value between multipath and deformation signals may not exist, multipath is usually inseparable from the low-frequency vibration signal using conventional frequency-domain filter methods. However, the multipath repeats in two sidereal days when the surroundings of a GPS antenna remain unchanged. This characteristic can be exploited to model and thus mitigate multipath effectively in dynamic deformation monitoring. Unfortunately, a major issue is that the degree of repeatability decreases as the interval between first day and subsequent days increases. To overcome this problem, we develop a new sidereal filtering referred to as reference EMD-ICA (EMD-ICA-R), where empirical mode decomposition (EMD) and independent component analysis (ICA) are jointly used to model multipath and renew the reference multipath. For the successful implementation of the EMD-ICA-R, an a priori denoised multipath signal is needed as a reference. We further propose to use the principal component analysis (PCA) method to extract more accurate reference multipath signal and form a combined PCA-EMD-ICA-R approach. Simulation experiments with a motion simulation platform were conducted, and the testing results indicate that the proposed methods can mitigate the multipath by around 67 % when a reliable reference multipath signal is extracted from a static situation. Furthermore, simulation experiments with different deformation signals added into the coordinate time series of three consecutive days show that the two proposed methods are also effective in a dynamic situation. Since wavelet filtering is used to denoise the reference multipath signals in the new approaches, simulation experiments with several wavelet filters are tested, and the results indicate that the PCA-EMD-ICA-R approach can work well with various wavelet filters.     

Precise tidal gravity recorded with superconducting gravimeters at stations Wuhan (China) and Kyoto (Japan)

 Three long series of tidal gravity observations, totalizing approximately 24 years and recorded with three superconducting gravimeters, T004, T008, and T009, at stations Wuhan (China) and Kyoto (Japan), are studied. The tidal amplitude factors and phase differences are determined precisely using Eterna and Nsv techniques. The precision of the main tidal amplitudes is at the same level of 0.01 μGal. The atmospheric gravity signals are corrected using the coefficients determined with a regression method between tidal gravity residual and station air pressure. The oceanic gravity signals are modeled based on five global oceanic models. It is found that the oceanic models developed by the analysis of measurements from Topex/Poseidon altimeters have the best fit to the superconducting gravimeter measurements, since the observed residuals and the discrepancies between the amplitude factors and the theoretical tidal models are reduced more significantly. The long-period gravity variations are dominated by the non-linear drift phenomena of the instruments, and the short-term variations in gravity are due to the background noise at the stations. Received: 20 January 2000 / Accepted: 15 September 2000     

远距离高精度GPS潮汐观测及垂直基准转换研究

为实现远岸潮汐精确监测及潮位海图高程转换,基于GPS事后动态处理技术(PPK)开展了远距离高精度潮位观测、提取及垂直基准面确定和转换模型构建方法研究。分别探讨了在锚定和走航情况下瞬时水面高程信号改正方法及潮位有效信息提取的最优截止频率,并给出了在不同情况下深度基准面大地高的计算方法模型及区域无缝深度基准面大地高构建模型。在实际试验中,基线距离在100km范围内,获得了基于深度基准的GPS潮位,精度优于10cm。     

Algorithm for Harmonic Tidal Analysis along T/P Tracks： Taking Differences of Observed Sea Surface Heights at Adjacent Points as Observations

An algorithm （differential mode） is presented for the improvement of harmonic tidal analysis along T/P tracks, in which the differences between the observed sea surface heights at adjacent points are taken as observations. Also, the observation equations are constrained with the results of the crossover analysis; the parameter estimations are performed at 0.1° latitude intervals by the least squares. Cycle 10 to 330 T/P altimeter data covering the China Sea and the Northwest Pacific Ocean （2°-50° N,105°-150° E） are adopted for a refined along-track harmonic tidal analysis, and harmonic constants of 12 constituents in 8 474 points are obtained, which indicates that the algorithm can efficiently remove non-tidal effects in the altimeter observations, and improve the precision of tide parameters. Moreover, parameters along altimetry tracks represent a smoother distribution than those obtained by traditional algorithms. The root mean squares of the fitting errors between the tidal height model and the observations reduce from 11 cm to 1.3 cm.     

GPS坐标时间序列时变振幅周期信号的Huber M估计

GPS时间序列周期信号的精准提取对趋势的估计具有重要的影响。相较于传统的常数振幅周期信号模型,已有研究表明GPS时间序列周期信号的振幅是随时间变化的。实际的GPS时间序列存在异常值,且在提取周期信号过程中会产生新的异常值。针对以上两点,该文提出了一种基于Huber函数M估计(HM)的GPS坐标时间序列时变振幅周期信号估计方法:采用关于时间的多项式函数来建立时变振幅模型,由HM方法及交替方向乘子法求解。通过模拟数据及实际GPS站点数据将HM方法与小波分解方法、奇异谱分析方法和滑动最小二乘方法进行比较,结果表明HM方法在估计精度上要优于其他3种方法,弥补了已有方法在时变振幅情形下会吸收噪声以及噪声较强时对周期信号提取能力较弱的不足。     

基于不同潮汐类型的不同时间尺度分潮结果精度分析

选取4种不同潮汐类型的验潮站实测潮位资料,对验潮零点在一定范围内变动对调和分析结果的影响进行分析,结果表明,一年的潮位数据中若后续6个月的数据发生10 cm、20 cm、30 cm零点漂移,各分潮振幅最大变化量为0.47 cm,迟角为0.16°。采用1~12个月不同中期尺度的实测数据,对调和结果的精度进行分析,结果表明,当潮位观测数据时间尺度小于6个月时,其4个主要分潮O_1、K_1、M_2、S_2振幅综合中误差在2 cm以上,迟角中误差在2°以上,具有显著的不稳定性;相同时间尺度的不同潮汐类型的潮位站潮位资料调和分析得到的主要分潮的振幅精度差异较大,迟角分布相似。当潮位观测数据时间尺度达到或多于6个月时,澳门站、汕尾站的分潮综合中误差分别为1.16 cm、0.61 cm,厦门站、北海站分别为2.90 cm和2.51 cm;各分潮迟角中误差均在2°内。当时间尺度超过9个月后,4个验潮站分潮振幅综合中误差均在2 cm以内,各分潮迟角中误差均在1°左右。     

Shallow-water loading tides in Japan from superconducting gravimetry

Gravity observations from superconducting gravimeters are used to observe loading effects from shallow-water tides on the Japanese east and west coasts. Non-linear third-diurnal and higher-frequency shallow-water tides are identified in the tide-gauge observations from these coastal areas. The most energetic constituents in the tide gauge observations are also seen in the gravity observations due to their loading effects on the deformation of the Earth. Even though the shallow-water tides at the Japanese east coast have an amplitude of only a few millimetres, they are still able to generate a loading signal at gravity sites located several hundred kilometres inland. In particular, the S₃, S₄ and S₅ solar tides occur in both gravity and tide gauge observations. It is indicated that in other shelf regions with large shallow water tides, the shallow water loading signals account for a significant signal, which should be taken into account.Acknowledgement The authors would like to thank the Hydrographic and Oceanographic Department (Japan Coast Guard), Japan Meteorological Agency and Hokkaido Development Agency for access to the tide-gauge data. Also, the Global Geodynamic Project Information System and Data Center (GGP-ISDC) is acknowledged for providing the gravity data.     

联合TOPEX/Poseidon与Geosat/ERM测高资料建立区域潮汐模型的研究

利用近十年的T/P测高数据来反演南海(8°~23°N,109°~120°E)九个主要分潮的潮汐参数,并计算了Geosat/ERM卫星对应的各主分潮的混叠周期及Rayleigh周期。根据潮汐参数提取的要求,选取了7个主分潮,为了克服混叠影响,将T/P沿迹点处的主要分潮间的5组差比关系引入到Geosat沿迹点处,并利用T/P提供的Sa模型去除Sa对M2的扰动影响。精度估计的结果表明,Geosat/ERM反演的潮汐参数的精度与传统的月分析结果的精度相近;因差比关系的捆绑,整个全日和半日潮族迟角偏差相近,这主要和Geosat/ERM的轨道设计有关。本文的方法可以应用于利用轨道调整后的T/P卫星的测高数据提取潮汐参数。     

Quantifying FES2004 S<Subscript>2</Subscript> tidal model from multiple space-geodesy techniques,GPS and GRACE,over North West Australia

Unmodeled sub-daily ocean S₂ tide signals that alias into lower frequencies have been detected in the analysis of gravity recovery and climate experiment (GRACE) space gravity fields of GRGS. The most significant global S₂ aliased signal occurs off the northwest coast of Australia in a shallow continental shelf zone, a region with high tidal amplitudes at a period of 161 days. The GRACE S₂ aliased equivalent water height grids are convolved with Green’s functions to produce GRACE aliased tidal loading (GATL) vertical displacements. The analysis of hourly global positioning system (GPS) vertical coordinate estimates at permanent sites in the region confirms the presence of spectral power at the S₂ frequency when the same ocean tide model (FES2004) was used. Thus, deficiencies in the FES2004 ocean tide model are detected both directly and indirectly by the two independent space geodetic techniques. Through simulation, the admittance (ratio of amplitude of spurious long-wavelength output signal in the GRACE time-series to amplitude of unmodeled periodic signals) of the GRACE unmodeled S₂ tidal signals, aliased to a 161-day period, is found to have a global average close to 100%, although with substantial spatial variation. Comparing GATL with unmodeled S₂ tidal sub-daily signals in the vertical GPS time-series in the region of Broome in NW Australia suggests an admittance of 110–130%.     

Estuarine sediment deposition during wetland restoration: A GIS and remote sensing modeling approach

Restoration is currently underway in the industrial salt flats of San Francisco Bay, California. Remote sensing of suspended sediment concentration and other GIS predictor variables were used to model sediment deposition within recently restored ponds. Suspended sediment concentrations were calibrated to reflectance values from Landsat TM 5 and ASTER satellite image data using three statistical techniques—linear regression, multivariate regression, and Artificial Neural Network (ANN) regression. Multivariate and ANN regressions using ASTER proved to be the most accurate methods, yielding r² values of 0.88 and 0.87, respectively. Predictor variables such as sediment grain size and tidal frequency were used in the Marsh Sedimentation (MARSED) model for predicting deposition rates. MARSED results show a root mean square deviation (RMSD) of 66.8 mm (<1σ) between modeled and field observations. This model was applied to a pond breached in November 2010 and indicated that the pond will reach sediment equilibrium levels after 60 months of tidal inundation.     

利用CEEMD分析中国沿海GNSS站高程时序变化

利用完备经验模态分解方法（CEEMD）对我国沿海地区6个GNSS基准站（2010—2018）的高程时序数据进行了处理分析。结果表明：CEEMD在高程时间序列分析中具有一定的优越性,可准确分解出各GNSS站高程时序中存在的周、月、季节、年等变化周期项,其中周年运动是主要贡献项,各站高程时间序列的短周期变化与潮汐变化周期具有密切关联性;沿海GNSS站的地面沉降既具有区域的一致性,又存在区域间差异性,其中D区DBJO、DZJJ站呈现先下降后上升的趋势,N区NZUH、NWZU站呈下降趋势,B区的BZMW呈上升趋势,而同海区的BLHT站则呈显著的下降趋势。     

水位改正中"虚拟验潮站"的快速内插

认为分带法水位改正就是在现有验潮站的基础上内插出若干“虚拟验潮站”，每个“虚拟验潮站”应有自己的编号，控制范围和水位数据，文中对分带法的新解释有利于计算机编程实现。     

利用EMD进行GNSS-MR潮位监测研究

GNSS-MR是一种新兴的遥感手段,可利用多路径效应探测地表环境。该方法已应用于潮位探测,取得了不错的效果。针对该方法存在的信号混杂问题,本文提出了利用经验模态分解法提取信噪比中的海水信号,避免了噪声信号及海岸反射信号的影响,并以布设在美国华盛顿州Friday Harbor海港的SC02测站为例,对比分析了利用EMD方法及传统方法反演得到的潮位数据。研究结果表明,该方法使LSP结果的RMSE相较于传统方法提升了5.36%,可用于提取较为纯净的海面信号,在一定程度上提高了反演精度。     

One centimeter-level observations of diurnal ocean tides from global monthly mean time-variable gravity fields

A method of analyzing GRACE satellite-to-satellite ranging data is presented which accentuates signals from diurnal ocean tides and dampens signals from long-period non-tidal phenomena. We form a time series of differences between two independent monthly mean gravity solutions, one set computed from range-rate data along strictly ascending arcs and the other set computed from data along descending arcs. The solar and lunisolar diurnal tides having alias periods longer than a few months, such as K ₁, P ₁, and S ₁, present noticeable variations in the monthly ascending and descending ‘difference’ solutions, while the climate-related signals are largely cancelled. By computing tidal arguments evaluated along the actual GRACE orbits, we decompose and estimate residual tidal signals with respect to our adopted prior model GOT4.7. The adjustment in the tidal height is small yet significant, yielding maximum amplitudes of 4 cm mostly under the Antarctic ice shelves and ~1 cm in general at spatial scales of several hundred kilometer. Moreover, the results suggest there are possible 1-cm errors in the tide model even over oceans well-covered by decades of radar altimetry missions. Independent validation of such small adjustments covering wide areas, however, is difficult, particularly with limited point measurements such as tide gauge.     

Impact of loading displacements on SLR-derived parameters and on the consistency between GNSS and SLR results

Displacements of the Earth’s surface caused by tidal and non-tidal loading forces are relevant in high-precision space geodesy. Some of the corrections are recommended by the international scientific community to be applied at the observation level, e.g., ocean tidal loading (OTL) and atmospheric tidal loading (ATL). Non-tidal displacement corrections are in general recommended not to be applied in the products of the International Earth Rotation and Reference Systems Service, in particular atmospheric non-tidal loading (ANTL), oceanic and hydrological non-tidal corrections. We assess and compare the impact of OTL, ATL and ANTL on SLR-derived parameters by reprocessing 12 years of SLR data considering and ignoring individual corrections. We show that loading displacements have an influence not only on station long-term stability, but also on geocenter coordinates, Earth Rotation Parameters, and satellite orbits. Applying the loading corrections reduces the amplitudes of annual signals in the time series of geocenter and station coordinates. The general improvement of the SLR station 3D coordinate repeatability when applying OTL, ATL and ANTL corrections are 19.5 %, 0.2 % and 3.3 % respectively, w.r.t. the solutions without loading corrections. ANTL corrections play a crucial role in the combination of optical (SLR) and microwave (GNSS, VLBI, DORIS) space geodetic observation techniques, because of the so-called Blue-Sky effect: SLR measurements can be carried out only under cloudless sky conditions—typically during high air pressure conditions, when the Earth’s crust is deformed, whereas microwave observations are weather-independent. Thus, applying the loading corrections at the observation level improves SLR-derived products as well as the consistency with microwave-based results. We assess the Blue-Sky effect on SLR stations and the consistency improvement between GNSS and SLR solutions when ANTL corrections are included. The omission of ANTL corrections may lead to inconsistencies between SLR and GNSS solutions of up to 2.5 mm for inland stations. As a result, the estimated GNSS–SLR coordinate differences correspond better to the local ties at the co-located stations when applying ANTL corrections.     

Methodology for the combination of sub-daily Earth rotation from GPS and VLBI observations

A combination procedure of Earth orientation parameters from Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) observations was developed on the basis of homogeneous normal equation systems. The emphasis and purpose of the combination was the determination of sub-daily polar motion (PM) and universal time (UT1) for a long time-span of 13 years. Time series with an hourly resolution and a model for tidal variations of PM and UT1-TAI (dUT1) were estimated. In both cases, 14-day nutation corrections were estimated simultaneously with the ERPs. Due to the combination procedure, it was warranted that the strengths of both techniques were preserved. At the same time, only a minimum of de-correlating or stabilizing constraints were necessary. Hereby, a PM time series was determined, whose precision is mainly dominated by GPS observations. However, this setup benefits from the fact that VLBI delivered nutation and dUT1 estimates at the same time. An even bigger enhancement can be seen for the dUT1 estimation, where the high-frequency variations are provided by GPS, while the long term trend is defined by VLBI. The estimated combined tidal PM and dUT1 model was predominantly determined from the GPS observations. Overall, the combined tidal model for the first time completely comprises the geometrical benefits of VLBI and GPS observations. In terms of root mean squared (RMS) differences, the tidal amplitudes agree with other empirical single-technique tidal models below 4 μas in PM and 0.25 μs in dUT1. The noise floor of the tidal ERP model was investigated in three ways resulting in about 1 μas for diurnal PM and 0.07 μs for diurnal dUT1 while the semi-diurnal components have a slightly better accuracy.     

基于短时间序列重力观测数据的潮汐改正方法

对于没有长期连续潮汐观测站和无精密潮汐模型的地区,研究高精度潮汐改正方法具有重要意义。给出了基于短时间序列重力观测数据的高精度潮汐改正方法,并利用全球动力学计划中TIGOConcepcion、Kamio-ka和Hsinchu三个台站的超导重力观测数据对该方法进行了试验分析。研究结果表明,利用一天或数天重力观测数据可建立高精度潮汐模型,其振幅因子和相位延迟解算精度分别优于0.01和0.5°,潮汐改正精度可以达到μGal量级,验证了该方法的正确性和有效性。本文方法为无精密潮汐模型区域的潮汐改正提供了新的途径。