Crustal motion and deformation in Greece from a decade of GPS measurements, 1993–2003

The Hellenic plate boundary region, located in the collision zone between the Nubian/Arabian and Eurasian lithospheric plates, is one of the seismo-tectonically most active areas of Europe. During the last 15 years, GPS measurements have been used to determine the crustal motion in the area of Greece with the aim to better understand the geodynamical processes of this region. An extended reoccupation network covering whole Greece has been measured periodically in numerous GPS campaigns since the late eighties, and a continuous GPS network has been operated in the region of the Ionian Sea since 1995. In this paper, we present a new detailed high-quality solution of continuous and campaign-type measurements acquired between 1993 and 2003. During the GPS processing, a special effort was made to obtain consistent results with highest possible accuracies and reliabilities. Data of 54 mainly European IGS and EUREF sites were included in the GPS processing in order to obtain results which are internally consistent with the European kinematic field and order to allow for a regional interpretation. After an overview of the results of the IGS/EUREF sites, the results from more than 80 stations in Greece are presented in terms of velocities, time series, trajectories and strain rates. Previous geodetic, geological and seismological findings are generally confirmed and substantially refined. New important results include the observation of deformation zones to the north and to the south of the North Aegean Trough and in the West Hellenic arc region, arc-parallel extension of about 19 mm/yr along the Hellenic arc, and compression between the Ionian islands and the Greek mainland. Due to continuous long-term observations of 4–8 years, it was possible to extract height changes from the GPS time series. In Greece, we observe a differential subsidence of the order of 2 mm/yr between the northern and central Ionian islands across the Kefalonia fault zone. The differential subsidence of the central Ionian islands with respect to the northwestern Greek mainland amounts to 4 mm/yr.     

The newest observational evidence on asymmetrical deformation of the Earth

IntroductionWhat is the shape of the Earth? Does it change continuously? It is a scientific question since the ancient times and is still being observed and explored at present. In 250 BC, Greek scholar Eratosthene supposed the shape of the Earth to be spherical according to the observations to the Sun and estimated the perimeter of the Earth to be 4 000 km (King-Hele, 1976) according to the camel-walking distance. Until the 16th century, the Earth was considered to be a very symmetrical …     

Applications géodésiques du système DORIS à l'Institut géographique national

IGN is in charge of the installation and maintenance of the DORIS orbit determination network. More recently, in collaboration with JPL, precise geodetic computations were performed. The goal of this paper is to recall the various historic contributions of IGN to the DORIS system in their international context and then to describe a new estimation technique developed for a multi-satellite mode, making full profit of a better modeling for satellites and ground clocks as well as tropospheric correction parameters. Derived geodetic results demonstrate a precision in the order of 1 cm for station positions. To cite this article: P. Willis et al., C. R. Geoscience 337 (2005).     

不同高程基准位差计算的严密理论研究

高程基准是大地测量参考框架的重要组成部分,也是数字地球基础框架的重要内容.但目前各个国家或地区使用的大多是局部高程基准,这严重影响了地球信息数据的全球共享机制.本文利用高程基准与重力位之间的关系,推导了不同高程系统之间的严密位差计算公式和近似计算公式.该理论将为我国和全球高程基准的统一提供理论支持.     

关于我国天测与测地VLBI网络未来建设的讨论

结合国内外VLBI技术发展的历史、现状与动态,从天体测量、空间大地测量和深空探测等角度,对我国天测与测地VLBI观测网络的未来建设进行了需求分析和测站配置技术指标分析。     

“深空大地测量导论”课程建设和教材编写的思考

介绍了"深空大地测量学导论"课程教材编写的背景、阐述了"深空大地测量学导论"教材编写的基本思路、总结了"深空大地测量学导论"教材的编写的特色.     

现代测量工程学发展现状与展望

从工程控制测量、大比例尺数字测图、施工放样、工业测量系统、变形监测和工程专题信息系统等6个方面,介绍了测量工程学的发展现状及取得的成就。可以看出,GPS测量技术和测量机器人技术已成为工程测量的主要应用技术,贯穿于各种工程中及工程测量的全过程;工业测量系统是测量工程学科最具活力的发展方向,在国防工业武器装备制造中发挥了巨大的作用。结合我院实际情况和今后学科二期建设的目标,指出了未来工测专业的发展方向。     

中国古代大地测量

古代测量是中国古代文明的重要组成部分，它是适应农耕与征战的需要最早发展起来的实用技术之一。中国大地测量源于距今近5000年的原始社会末期的三皇五帝时代。几千年来，中国大地测量经历了从步量、丈量到立杆测影、仪器观测的发展过程。距今2000年的西汉时期，发明了浑天仪，开始了使用仪器测量地面点地理坐标的新阶段。公元724年，僧人一行与南宫说在黄河中游的平坦地区进行了世界上最早的子午线测量。16世纪后期，意大利人利玛窦带来了西方的测量技术，从此开始了中国传统大地测量与西方测量方法并行、融合的进程。明末清初，利用天文测地的方法在全国范围内测定了几十个经纬度点，为地图绘制提供了控制基础。天圆地方是中国古代最典型宇宙观，是中国古代测量与制图中未能考虑地球曲率的认识根源。简言之，中国古代大地测量成就辉煌，特色明显，与西方古代测量并驾齐驱。     

Improved ocean-geoid resolution from retracked ERS-1 satellite altimeter waveforms

The ocean geoid can be inferred from the topography of the mean sea surface. Satellite altimeters transmit radar pulses and determine the return traveltime to measure sea-surface height. The ERS-1 altimeter stacks 51 consecutive radar reflections on board the satellite to a single waveform. Tracking the time shift of the waveform gives an estimate of the distance to the sea surface. We retrack the ERS-1 radar traveltimes using a model that is focused on the leading edge of the waveforms. While earlier methods regarded adjacent waveforms as independent statistical events, we invert a whole sequence of waveforms simultaneously for a spline geoid solution. Smoothness is controlled by spectral constraints on the spline coefficients. Our geoid solutions have an average spectral density equal to the expected power spectrum of the true geoid. The coherence of repeat track solutions indicates a spatial resolution of 31  km, as compared to 41  km resolution for the ERS-1 Ocean Product. While the resolution of the latter deteriorates to 47  km for wave heights above 2  m, our geoid solution maintains its resolution of 31  km for rough sea. Retracking altimeter waveform data and constraining the solution by a spectral model leads to a realistic geoid solution with significantly improved along-track resolution.