Local normal height connection across sea with ship-borne gravimetry and GNSS techniques

Heights as the basic geographical information are very important to study marine geophysics, geodesy and oceanography. Based on the astronomical leveling principle, we put forward a new method to unify the normal height (NH) datum along one ship route across sea with the ship-borne gravimetry and global navigation satellite system (GNSS) techniques. Ship-borne gravimeter can precisely measure gravity anomalies and the GNSS technique is used to measure precise sea surface heights (SSHs) along the ship track across sea. Precisions of ship-borne gravities and SSHs are improved with the colinear adjustment. To remove the effects of sea wave and wind, the Gaussian filter is used to filter residuals both between the ship-borne and modeled gravities from EGM2008 to degree 2160, and the measured and modeled SSHs from DTM10MSS, respectively. Deflections of the vertical (DOVs) along the ship route are estimated from the measured gravities with the least squares collocation method. The astro-geodetic survey is made on continent and island to improve the accuracy of DOVs along the route. We use the new method to connect NHs on the coastal sea of Shandong Peninsula, China. The results indicate that the method is very efficient to precisely connect the NH along the ship route across sea.     

无控制岛礁高程的确定

通过对EGM96、WDM94和GFZ重力场模型计算的测区重力(似)大地水准面的比较,选取最适合测区的重力场模型。并利用所选重力场模型,用移去-恢复的方法计算各控制点和待定点的大地水准面高;根据GPS/水准点高程异常数据计算其改正数,按照距离倒数加权内插法将改正数传递到待定点,由于待定点的大地高、模型大地水准面高已知,进而可以求得其高程。     

High Precision Geoid Models HKGEOID-2000 for Hong Kong and SZGEOID-2000 for Shenzhen,China

High precision geoid models HKGEOID-2000 for Hong Kong and SZGEOID-2000 for Shenzhen, China, have been developed with a hybrid approach of so-called sequential processing, using high precision GPS/leveling data, land and sea gravity anomalies, and digital terrain models. These two local geoid models have the same 1-km resolution. The estimated accuracy (external accuracy) is better than 1.7 cm for HKGEOID-2000 and 1.4 cm for SZGEOID-2000. Some common areas are covered by HKGEOID-2000 and SZGEOID-2000. So these two geoid models, along with high quality GPS/leveling data collected on the overlapping areas, can be used to detect the systematic bias between HKGEOID-2000 and SZGEOID-2000, as well as the difference between Hong Kong Principal Datum and 1956 yellow sea height datum of China, yielding RMS errors of 1.011 m and 1,003 m, respectively. Moreover, HKGEOID-2000, along with GPS ellipsoidal heights, is employed to determine the errors of the “orthometric heights” from purely trigonometric heighting, yielding an RMS error of 0.102 m. The combination of SZGEOID-2000 and GPS ellipsoidal heights has been used to replace the traditional spirit leveling and mapping, called GPS mapping.     

A geodetic investigation of the British sea slope anomaly

Abstract

A project was initiated in 1986 to investigate an apparent significant discrepancy between geodetic and oceanographic leveling determinations of mean sea level around the coast of Great Britain. In oceanographic terms this discrepancy is equivalent to a sea slope in a North‐South direction.

The project, which lasted for 3 years, has been carried out in conjunction with research groups at the University of Edinburgh, the Proudman Oceanographic Laboratory, and the Ordnance Survey of Great Britain. It has involved combining Global Positioning System (GPS)‐derived ellipsoidal height differences with a high‐precision geoid, leading to an independent determination of the orthometric heights of tide gauges along the east coast of Great Britain.

A major GPS campaign was observed in May 1988. Measurements were made at time gauges between Leith and Lowestoft while simultaneously making measurements at fiducial sites. The results of the 1988 and subsequent campaigns are presented and discussed, and details are given of further observation campaigns to monitor the vertical movement of tide gauges around the coast of Britain by GPS.     

High Precision Geoid Models HKGEOID-2000 for Hong Kong and SZGEOID-2000 for Shenzhen, China

High precision geoid models HKGEOID-2000 for Hong Kong and SZGEOID-2000 for Shenzhen, China, have been developed with a hybrid approach of so-called sequential processing, using high precision GPS/leveling data, land and sea gravity anomalies, and digital terrain models. These two local geoid models have the same 1-km resolution. The estimated accuracy (external accuracy) is better than 1.7 cm for HKGEOID-2000 and 1.4 cm for SZGEOID-2000. Some common areas are covered by HKGEOID-2000 and SZGEOID-2000. So these two geoid models, along with high quality GPS/leveling data collected on the overlapping areas, can be used to detect the systematic bias between HKGEOID-2000 and SZGEOID-2000, as well as the difference between Hong Kong Principal Datum and 1956 yellow sea height datum of China, yielding RMS errors of 1.011 m and 1,003 m, respectively. Moreover, HKGEOID-2000, along with GPS ellipsoidal heights, is employed to determine the errors of the “orthometric heights” from purely trigonometric heighting, yielding an RMS error of 0.102 m. The combination of SZGEOID-2000 and GPS ellipsoidal heights has been used to replace the traditional spirit leveling and mapping, called GPS mapping.     

RTM Gravity Forward-Modeling Using Topography/Bathymetry Data to Improve High-Degree Global Geopotential Models in the Coastal Zone

We apply the residual terrain modeling (RTM) technique for gravity forward-modeling to successfully improve high-resolution global gravity fields at short spatial scales in coastal zones. The RTM scheme is combined with the concept of rock-equivalent topography, allowing to use a single uniform constant mass-density in the RTM forward-modeling, both at land and sea. SRTM30_PLUS bathymetry is merged with higher-resolution SRTM V4.1 land topography, and expanded into spherical harmonics to degree 2160, yielding a new and consistent high-degree RTM reference surface. The forward-modeling performance is demonstrated in coastal zones of Greece and Canada using ground-truth vertical deflections, gravity from land and shipborne gravimetry, and geoid heights from GPS/leveling, with improvements originating from bathymetry clearly identified. We demonstrate that the SRTM30_PLUS bathymetry carries information on gravity field structures at spatial scales less than 5 arc minutes, which can be used to augment EGM2008 in (rugged) coastal zones, both over land and marine areas. This may be of value (i) to partially reduce the signal omission error in EGM2008/GOCE-based height transfer in areas devoid of dense gravity data, (ii) to fill the gap between land gravity and shipborne gravity along rugged coastlines, and (iii) for the development of next-generation altimetric gravity fields.     

西北太平洋中国沿海海面倾斜及其机理初探

海面倾斜与高程基准密切相关,它已经受到大地测量学界和海洋学界的重视.进一步讨论了大地水准的测量精度,指出了大地(几何)水准与沿海验潮资料的不符是由于海面的倾斜;分析了海面倾斜的机理,其中包括海流、海水密度分布、气压、台风引起的破碎波等的作用;提出了用海水异常密度的三维分布计算大地水准面的扰动,实质上它反映了海面的倾斜,该量占大地水准测量结果的73%,这进一步说明密度的异常乃是我国沿海海面倾斜的主要原因.     

Quasi-Geoid Near Xisha Islands by the Geo-Potential Propagating Technique

Height datum is an important part of national geodetic network. Establishment of a unified national land and sea elevation benchmarks and implementation of height datum connection between the Chinese mainland and offshore islands are issues that need to be resolved in geomatics and marine sciences. Derived from basic definition of elevation datum and relationship between geo-potential and normal height, the scientific theory and algorithm for transferring height datum from mainland to islands with geo-potential are elaborated. The accuracy of geo-potential difference is discussed using a numerical analysis method. We also give criteria to choose virtual leveling routines and algorithm to give optimized results. One experiment in the China seas, among 26 tidal gauge stations in the sea coast of the mainland with known normal height, has confirmed the reliability and accuracy of the method developed in this paper. Further optimizations for improving accuracy of island elevation are also introduced. Distribution of quasi-geoid near Xisha Islands is also given with this method.     

远海航渡式水深测量水位改正方法研究

针对远海航渡式水深测量作业中的潮汐改正难题,基于全球潮汐场DTU10模型及GPS无验潮测深两种改正模式,通过潮汐场预报精度评估、验潮站实测数据比对分析以及GPS大地高计算潮汐值等多种手段,开展了大范围、长时段、单测线情况下水深测量水位改正研究,形成了一套适用性强的航渡水深测量水位改正方法与流程,为面向全球的海洋水深测量资料处理提供了潮汐、垂直基准和水位归算的方法和技术支持。     

Evaluating the Performance of Using PPK-GPS Technique in Producing Topographic Contour Map

The Global Positioning System (GPS) is considered as one of the most powerful tools that are used in geodetic works. It is increasingly considered as an alternative tool for conventional surveying techniques. The goal of this research paper is to produce a methodology for generating topographic contour maps using the post-processed kinematic differential GPS technique (PPK-GPS). The performance of this technique is assessed by comparing it with the traditional spirit-leveling technique taking into consideration the accuracy, time, and cost. The study area is located along the Mediterranean coast in the Rosetta area of the middle Delta in Egypt with a total area of about 39 km². The field work includes 14 control points and about 50,000 PPK observations. In addition, 20 check cross sections that extend along the coastal line from Rosetta to El Burullus cities were observed using both spirit-leveling and GPS-PPK techniques. The results of the comparison indicate that the PPK-GPS technique can be used instead of spirit leveling in producing a topographic contour map with an accuracy of about 20 cm in orthometric height. We find that the PPK-GPS technique reduces the estimated time of leveling works in our study area by about 70%.     

夏季琼州海峡表层海水二氧化碳分压时空变化

采用船载海?气CO₂连续观测系统于2011年和2014年夏季在琼州海峡开展了现场观测,分析研究了表层海水二氧化碳分压(pCO₂)时空变化及其影响因子。2011年和2014年夏季pCO₂分别为(516±29) μatm和(533±15) μatm,海?气CO₂交换通量分别为(8.4±1.7) mmol/(m2·d)和(4.5±0.4) mmol/(m2·d),均是大气CO₂的强源,高于相邻及相似海域,主要受控于东口海域上升流和海峡中部狭管效应。2011年夏季东口上升流增大pCO₂的同时也促进了浮游植物繁殖,光合作用吸收水体CO₂,降低了pCO₂,而且受其影响,西口口门附近叶绿素a和溶解氧含量陡增,pCO₂突降。2014年夏季东口海域上升流较弱,且观测海域垂直混合作用显著,pCO₂和溶解氧分布特征与2001年夏季明显不同。海峡中部狭管效应造成水体输运速率大、混合作用强,浮游植物“来不及”生长,pCO₂较高。     

典型海湾区域海洋测绘中垂直基准的构建研究

以典型的海湾区域为例,基于可行实用原则并保证精度的情况下,对陆海垂直基准的传递和统一进行研究,结合平均海面传递和GPS高程拟合方法,构建了典型海湾区域统一的海洋测绘垂直基准,实现了海湾区域海洋测绘中海岸地形图和水深图的无缝拼接。通过实例研究表明:研究路线正确,选择方法可行,成果精度符合《规范》要求,满足海湾区域测图的需要。     

2018年春节期间琼州海峡持续性大雾监测分析

2018年春节期间,琼州海峡持续6 d（2月15—20日）有雾,最低能见度不足200 m。主要从气象卫星监测上分析此次琼州海峡持续性海雾的时间演变特征,并从大气海洋条件分析形成持续性海雾的原因,得出如下结论：1）2018年2月华南东侧西太平洋海面温度较常年同期偏高,有3个暖海面温度距平中心,为持续性大雾提供暖湿气流;2）此次持续性大雾过程琼州海峡位于均压场,但西南低涡起着辅助的作用,致使海洋性的南风在边界层抵御了干燥的大陆性气团,利于维持边界层的湿度;3）低层流场为暖湿气流,925 hPa近地面湿层上空有一个干中心维持,“上干下湿”的湿度层结有利于海雾维持和向上发展形成一定厚度的海雾;4）低云增加和弱降水是使18日全天海雾得以维持的重要因素。     

Unification of vertical datums by GPS and gravimetric geoid models using modified stokes formula

In general, neighboring vertical datums can be compared directly at one or more common points on the border between the datums. This direct method requires leveling and gravity measurements. Such a direct connection is not possible if the datums are separated by an ocean or another body of water. Then a rigorous mathematical model, an indirect approach, may be useful. In order to connect regional vertical datums, a rigorous mathematical model is derived based on a method by Rummel and Teunissen. In this study, two vertical datums are connected indirectly by means of a combination of precise geocentric positions of tide gauge sites and their geoid heights in one geocentric coordinate system and their height values in the respective height datums. This method is used to connect the Swedish and the Finnish height systems. The difference between Swedish RH70 and the Finnish N60 height systems is estimated to —12.1±2.7 cm. The results are mostly in good agreement with those of the direct approach by Sjöberg and by Ekman and the indirect approach by Pan and Sjöberg.     

Geodetic determination of the surface topography of the Baltic Sea

The Baltic Sea Level Project is an international scientific observation program to unify the vertical datums of the countries of the Baltic Sea with GPS measurements. In total, 35 tide gauges on shores and islands of the Baltic were occupied with GPS in 1993. After computing a new gravimetric geoid over the Baltic Sea, it was possible to unify the datums as well as to calculate the orthometric heights and the sea surface topography values for the tide gauge stations. The results obtained are shown.     

基于EGM模型的多波束无验潮测深技术应用

多波束水深测量中受潮汐因素的影响,测量垂直基准是变化的,具有瞬时性。传统多波束测量,需在测区内设立一个或多个验潮站进行同步水位观测,最终将水深归算到深度基准面上。针对多波束水深测量中垂直基准转换的复杂性问题,文中基于地球重力场模型,结合测区内实测的GNSS/水准数据,通过插值算法建立了测区范围内似大地水准面精化模型,构建了多波束无验潮水深测量的垂直基准转换模型。通过实例表明,该方法有效地消除了潮汐、动态吃水及涌浪等因素影响,直接获取深度基准面的水深值,提高工作效率,可满足近岸多波束水深测量的工作需求。     

用温盐资料研究夏季南海水通过琼州海峡进入北部湾的特征

夏季琼州海峡水交换向来存在两种观点:一种认为在西南风作用下,琼州海峡水交换从西向东;另一种观点则和上述相反。我们通过琼州海峡东部水域温盐分布和沿岸海洋站同步观测资料的对比发现,夏季北部湾的涠州岛盐度变化规律和琼州海峡东部、琼州海峡中部变化规律一致。由此证明,夏季南海水通过琼州海峡进入北部湾的事实。北海略受影响。而远离琼州海峡的龙门和白龙尾两站,则更多反映夏季陆地水文规律。由此证明,夏季南海水通过琼州海峡进入北部湾的事实。     

The Role of GNSS Vertical Velocities to Correct Estimates of Sea Level Rise from Tide Gauge Measurements in Greece

In this study, we show how the Global Navigation Satellite System (GNSS)-derived vertical velocities contribute to the correction of tide gauge (TG) measurements used for the sea level rise estimation in Greece. Twelve sites with records of local sea level heights are processed in order to estimate their trend. Certain error sources related to TGs, e.g. equipment changes, data noise, may lead to biased or erroneous estimations of the sea level height. Therefore, it would be preferred to follow a robust estimation technique in order to detect and reduce outlier effects. The geocentric sea level rise is estimated by taking into account the land vertical motion of co-located GNSS permanent stations at the Hellenic area. TGs measure the height of the water relative to a monitored geodetic benchmark on land. On the other hand, using GNSS-based methods the vertical land motion can be derived. By means of extended models fitted to the GNSS time-series position, obtained from seven years of continuous data analysis, periodic signals are well described. The synergy of the two co-located techniques results in the correction of TG relative sea level heights taking into account the GNSS vertical velocities and consequently obtaining the conversion to absolute (geocentric) sea level trend.     

琼州海峡东部水进入北部湾对广西沿海环流的影响

本文通过对琼州海峡东部水域温盐资料和沿岸海洋站同步观测资料的对比发现：夏季,广西涠洲岛盐度变化规律和琼州海峡东部、中部变化规律一致,广西北海略受影响,而远离琼州海峡的龙门和白龙尾两站,则更多反映夏季陆地水文规律。同时,采用琼州海峡多年海流资料和涠洲岛定点站及近期测流站的海流观测资料对比看出,琼州海峡冬夏季余流方向仍然是自东向西。结合数值模拟计算结果,同样得出琼州海峡东部水自东向西进入北部湾的事实。这些温盐分布特征和余流观测结果进一步证实：粤西沿岸流是琼州海峡水向西输运的主要来源,形成粤西沿岸流这种现象的根源在于珠江冲淡水的西向流,它们通过琼州海峡进入北部湾,加强了北部湾北部气旋式环流的形成。夏季,在强的西南风作用下,产生较强北部湾西岸北向沿岸流,促使低盐冲淡水向外海输运,然后在东部涠洲岛附近形成更大范围内气旋式环流。琼州海峡东部水进入北部湾对广西沿海环流影响的研究,直接向琼州海峡冬夏季水体输运方向的传统结论提出了新的挑战。     

跨海高程基准传递方法及其精度研究

利用GPS水准法和同步改正法实现了跨海高程基准的传递。GPS传递结果与同步改正法传递结果相差3cm。结果表明,GPS结合大地水准面精化技术实现跨海高程基准传递省时省力、方便可靠。