用CSR4.0+CS模型计算海潮负荷改正

介绍了CSR3．0与CSR4．0 CS海潮模型，并对两模型进行了分析和实算比较，认为CSR4．0 CS比CSR3．0海潮模型精度更高，在计算中国测站海潮改正时，顾及中国近海海潮图是必要的。对我国第二期水准路线用CSR4．0 CS模型计算了海潮负荷改正，结果表明：海潮负荷对高精度水准测量的影响，主要取决于水准路线的近海位置，越是近海地区越明显；在近海区域，这项改正不能忽略。     

Evaluation of the accuracy of the EIGEN-1S and -2 CHAMP-derived gravity field models by satellite crossover altimetry

Since the advent of CHAMP, the first in a series of low-altitude satellites being almost continuously and precisely tracked by GPS, a new generation of long-wavelength gravitational geopotential models can be derived. The accuracy evaluation of these models depends to a large extent on the comparison with external data of comparable quality. Here, two CHAMP-derived models, EIGEN-1S and EIGEN-2, are tested with independent long-term-averaged single satellite crossover (SSC) sea heights from three altimetric satellites (ERS-1, ERS-2 and Geosat). The analyses show that long-term averages of crossover residuals still are powerful data to test CHAMP gravity field models. The new models are tested in the spatial domain with the aid of ERS-1/-2 and Geosat SSCs, and in the spectral domain with latitude-lumped coefficient (LLC) corrections derived from the SSCs. The LLC corrections allow a representation of the satellite-orbit-specific error spectra per order of the models spherical harmonic coefficients. These observed LLC corrections are compared to the LLC projections from the models variance–covariance matrix. The excessively large LLC errors at order 2 found in the case of EIGEN-2 with the ERS data are discussed. The degree-dependent scaling factors for the variance-covariance matrices of EIGEN-1S and –2, applied to obtain more realistic error estimates of the solved-for coefficients, are compatible with the results found here.     

Second Tesseral Harmonic Torque Due to the DynamicS of the Oceanic Surface Layer as Detected by TOPEX/POSEIDON Altimetry 1993-2000

Estimates of the second tesseral torque due to the variations in the radial space position of the mean ocean surface as monitored by TOPEX/POSEIDON altimeter system are derived. The magnitude of the studied torque may be compared to the tidal torque and to the tesseral torque caused by deformations due to the Earths rotation. However, such torque estimates strongly depend on the thickness of the ocean surface layer adopted in the spherical model of which the dynamics is believed to be responsible for the derived torque. The dependence on the thickness is discussed.     

Mapping nonlinear shallow-water tides: a look at the past and future

Overtides and compound tides are generated by nonlinear mechanisms operative primarily in shallow waters. Their presence complicates tidal analysis owing to the multitude of new constituents and their possible frequency overlap with astronomical tides. The science of nonlinear tides was greatly advanced by the pioneering researches of Christian Le Provost who employed analytical theory, physical modeling, and numerical modeling in many extensive studies, especially of the tides of the English Channel. Le Provost’s complementary work with satellite altimetry motivates our attempts to merge these two interests. After a brief review, we describe initial steps toward the assimilation of altimetry into models of nonlinear tides via generalized inverse methods. A series of barotropic inverse solutions is computed for the M tide over the northwest European Shelf. Future applications of altimetry to regions with fewer in situ measurements will require improved understanding of error covariance models because these control the tradeoffs between fitting hydrodynamics and data, a delicate issue in coastal regions. While M can now be robustly determined along the Topex/Poseidon satellite ground tracks, many other compound tides face serious aliasing problems. In memory of Christian Le Provost     

A new insight on the decreasing sea level trend over the Ionian basin in the last decades

Altimetry measurements over the Ionian region and tide gauge records along the southern Italian coasts have been combined to analyse the negative sea level trend over the Ionian basin in the last decades. The apparent decreasing trend should be better understood as an abrupt sea level drop in 1998 probably linked to changes in the surface circulation in the Ionian basin induced by the Eastern Mediterranean Transient, which changed from anticyclonic to cyclonic about March 1998. From then onwards, a rising rate of 7.9 ± 0.9 mm/year is observed over the basin.     

基于TOPEX/Poseidon卫星数据的江河流量测算

TOPEX／Poseidon卫星的原始目的是测量海面高度变化信息,为海洋监测服务。作者通过假设基准面的方法,将由TOPEX／Poseidon卫星数据估算的下垫面水位相对变化信息转化为”水位”系列并建立了由TOPEX／Poseidon得出的“水位”与相邻水文站实测流量间的相关关系,进而实现了由TOPEX／Poseidon卫星数据估算河道流量的目的。利用1998～1999年TOPEX／Poseidon在长江下游大通附近的过境数据和对应年份大通水文站实测流量数据,验证了本方法的可行性。研究结果表明：在长江下游河道地区,由TOPEX／Poseidon卫星数据可定量估算出山河流流量信息。     

Jason-2测高卫星对湖泊水位的监测精度评价

湖泊水位是评估湖泊水量变化的重要指标。本文以洪泽湖、高邮湖及洞庭湖为研究对象,利用集中度的概率密度函数方法(CPDF)来提高Jason-2测高数据精度,分析了降水量与各个湖泊水位变化的相关性,并基于实测水位数据对比评价了Jason-2测高卫星原始GDR数据和CPDF方法处理后的卫星数据的精度。结果表明:①Jason-2原始GDR数据点的分布存在疏密之分,大部分数据分布相对集中,且有一定的周期变化,但评价结果显示精度较差,故原始GDR数据不能直接用于湖泊水位监测;②CPDF方法可以极大提高测高卫星的水位数据精度,洪泽湖与高邮湖的均方根误差分别由1.92 m与1.74 m减少到了0.32 m和0.36 m,相关系数由0.28和0.04提高到了0.85和0.72。对于南北宽度较窄且日水位变化较大的湖泊(如洞庭湖),CPDF方法提高原始GDR结果的精度有限;③洞庭湖降水与水位相关性最强,高邮湖次之,而洪泽湖降水与水位成不显著的负相关,是洪泽湖水利工程对于水位的调节导致了这一结果。本研究对于利用测高卫星获得湖泊水位值,进而对湖泊进行动态监控,特别是在填补资料匮乏地区湖泊水位数据方面具有重要意义。     

卫星测高技术应用研究回顾与展望

简要介绍了笔者所在单位近十年来密切跟踪世界发展动态,灵活运用高新技术,致力于卫星测高技术应用研究所取得的一些有理论意义和实用价值的成果,这些成果主要包括四个方面：卫星测高径向轨道误差时域和空域特征分析、卫星测高反演海洋重力场、卫星测高反演海底地形以及利用测高重力异常扩展超高阶地球位模型研究成果。最后对这一研究领域未来的发展方向作了展望。     

利用GPS三频数据计算电离层垂直总电子含量变化率

研究了通过采样间隔为1 s的GPS三频载波相位观测数据计算1 Hz电离层垂直总电子含量变化率(RVTEC)的方法,推导了直接采用双频载波相位观测量计算RVTEC的公式,对一般空间环境与电离层活动剧烈两种条件下L1L2、L1L5、L2L5三种载波相位组合计算的RVTEC进行了一致性分析,给出了通过三频载波相位观测数据计算电离层RVTEC的修正方法,比较了X射线太阳耀斑期间RVTEC与由传统方法计算的总电子含量变化率(ROT)响应,在双星串飞编队测高模式下对计算方法进行了应用.结果表明,L1L2、L1L5两种组合之间的一致性较好,由L1L2、L1L5组合计算的RVTEC的中误差约为0.004 TECu/s,RVTEC较ROT更能体现TEC变化的细节,在双星串飞编队测高模式下海面高梯度的计算中,电离层延迟之差可以忽略.     

Improving gravity anomalies over China marginal sea from retracked Geosat and ERS-1 data

The quality of altimeter data and ocean tide model is critical to the recovery of coastal gravity anomalies. In this contribution, three retracking methods (threshold, improved threshold and Beta-5) are investigated with the aim of improving the altimeter data over a shallow water area. Comparison indicates that the improved threshold is the best retracking method over China Sea. Two ocean tide models, NAO99b and CSR4.0, are analyzed. Results show that different tide models used in the processing of altimeter data may result in differences more than 10 mGal in recovered coastal gravity anomalies. Also, NAO99b is more suitable than CSR4.0 over the shallow water area of China Sea. Finally, gravity anomalies over China Sea are calculated from retracked Geosat/GM and ERS-1/GM data by least squares collocation. Comparison with shipborne gravimetry data demonstrates that gravity anomalies from retracked data are significantly superior to those from non-retracked data. Our results have the same order as the other two altimeter-derived gravity models: Sandwell&Smith(V16) and DNSC08.