One-Centimeter Orbit Determination for Jason-1: New GPS-Based Strategies

The U.S./French Jason-1 satellite is carrying a state-of-the-art GPS receiver to support precise orbit determination (POD) requirements. The performance of the Jason-1 “BlackJack” GPS receiver was strongly reflected in early POD results from the mission, enabling radial accuracies of 1–2 cm soon after the satellite's 2001 launch. We have made further advances in the GPS-based POD for Jason-1, most notably in describing the phase center variations of the on-board GPS antenna. We have also adopted new geopotential models from the Gravity Recovery and Climate Experiment (GRACE). The new strategies have enabled us to better exploit the unique contributions of the BlackJack GPS tracking data in the POD process. Results of both internal and external (e.g., laser ranging) comparisons indicate that orbit accuracies of 1 cm (radial RMS) are being achieved for Jason-1 using GPS data alone.     

“3S”技术在土地利用数据更新及建库中的应用

随着“3S”技术的成熟,“3S”技术已经在各个行业、各个领域得到了广泛的应用.本文简要介绍了“3S”技术在我国的发展现状及我国土地利用数据库的建设概况,并阐述了“3S”技术在土地利用数据库更新及建库中的应用,同时,展望了“3S”技术综合运用在国土资源管理中的前景.     

High-precision geoid determination in small areas: A case study in Doñana National Park (Spain)

Doñana National Park is an area of approximately 500 km² located on the SW coast of Spain that shows one of the greatest geoid gradients on the entire Iberian Peninsula, due to its peculiar tectonic characteristics. So, it is necessary to elaborate an accurate geoid model that can be used with GPS for precise surveying, since the existing ones are insufficient, due to their poor resolution and their limited adaptation to a small area with such a strong gradient. The least squares prediction method was tested in order to obtain the undulation from GPS/orthometric points. The results obtained were unsatisfactory because of the strong geoid gradient. In order to improve accuracy the remove-restore technique was used. Global geopotential model EIGEN-CG01C and a Digital Elevation Model (DEM) with a 25 × 25 m resolution and an accuracy better than 3 m were used. Thus, the final geometrical geoid obtained reaches the precision required by other disciplines (3 cm in any point within the Park). Particularly, the geoid model has allowed for the acquisition of a precision DEM that is essential to formulate a hydrodynamic model for the Doñana marsh functions.     

利用GPS观测的时间序列资料反演地壳地幔黏性结构

地球介质的黏度是地球动力学研究中的重要参数. 在考虑震后震源区介质物性变化的情况下,本文提出利用GPS观测的时间序列资料反演地壳、地幔黏度的方法. 计算中,将遗传算法与Marquardt法相结合,利用遗传算法搜索结果作为Marquardt法反演的初始模型,运用微扰法形成Jacobian矩阵. 根据余震分布及地震波速度变化确定震源区的范围及介质的物性变化情况,利用黏弹性有限单元模型（Maxwell体）及台湾集集地震后GPS观测的时间序列数据,反演了台湾地区地壳、地幔的黏性系数. 反演计算及数值实验表明,该方法反演黏度的效率高,稳定性好. 反演结果初步显示台湾地区的地壳、地幔的黏度分别为1.2×1018Pa·s和3.6×1019 Pa·s.     

福建地壳运动观测网络观测成果初步分析

利用最新GAMIT软件,对福建省地壳运动观测网络的厦门、福州、泉州、龙岩、南平5个GPS基准站2004年3月1日至2005年3月6日的观测资料在ITRF2000全球坐标系统框架下,使用IGS精密星历数据及其核心观测站的坐标和运动速率为控制参数进行了统一解算,并利用GLOBK软件进行联合平差,得到了5个测站的观测精度。结果表明,福建地区形变南强北弱、东强西弱,且该地区随中国大陆较均匀地向SE（SEE）方向运动。     

2001年昆仑山口西M_S 8.1地震前背景形变场的模拟研究

文中以东昆仑断裂带周围分布的27个GPS站点的地壳运动速率矢量为约束,利用半无限弹性空间三维断裂位错模型,反演了东昆仑断裂、柴达木盆地北缘断裂、玛尼-玉树断裂和玛尔盖茶卡断裂带在2001年昆仑山口西MS8.1地震之前的运动速率,并认为这些断裂带以反演出的运动速率错动所形成的形变场可以作为震前的背景地壳形变场。基于这一具有构造意义的背景速度场资料,计算了区域地壳应变率场和地震矩累积率场。结果表明,昆仑山口西地震前,东昆仑断裂的东西大滩段和玛尼-玉树断裂西段为该区域2个最显著的地震矩累积率高值区,其中东昆仑断裂的东西大滩段高值区为后来的昆仑山口西MS8.1地震的发震段     

Epicenter and magnitude of large earthquake determined from high-rate GPS observations: A case study of the 2008 M8.0 Wenchuan earthquake

For earthquake and tsunami early warning and emergency response,the earthquake epicenter and magnitude should be determined rapidly and correctly.Using high-rate GPS observations,we can readily obtain precise and high resolution displacement time series and the seismic waveforms during the earthquake.In this paper,a new algorithm is proposed for estimating the earthquake epicenter and magnitude with the seismic waveforms derived from high-rate GPS data during the earthquake.A case study of the 2008 Wenchuan earthquake is conducted from 1 Hz GPS data and the epicenter and magnitude are determined.Compared with the results issued by the China Seismological Bureau,the estimation error of the epicenter and the magnitude is about 12 km and 0.1 magnitude unit,respectively.It has shown that high-rate GPS could be a new tool feasible for estimating the earthquake epicenter and magnitude,independent of or combined with seismometers.     

Regional Stress Field and Seismic Dynamics Along the Border Zone Between Fujian, Guangdong and Jiangxi Provinces

The regional stress field and seismic dynamics along the border zone between Fujian, Guangdong and Jiangxi Provinces are studied based on the seismo-geological data, GPS measurement, and seismicity. The results show that: (1) the principal compressional stress of the stress field is oriented in NW-SE direction and the principal extensional stress is in NE-SW direction; (2) the WNW-ward compression and collision of the Philippine Sea Plate to the eastern coast of Taiwan Island are the most direct and most important dynamic source for preparation and occurrence of strong earthquakes in the Taiwan area and along the border zone between Fujian, Guangdong and Jiangxi Provinces.     

Constructing temporal and spatial water vapor figures by GPS remote sensing along slant rays

A Global Positioning System (GPS) receiver can generally track 5-7 rays from GPS satellites at any moment, and water vapor along these ray paths (slant-path water vapor, SWV) may be retrieved using the methods developed in recent years. This paper suggests two new parameters-absolute vertical SWV (VSWV) and relative VSWV derived from SWV, and their temporal and spatial figures can reflect the heterogeneous distribution and variation of water vapor field. This approach has been applied to the weather diagnoses in a severe storm event in Beijing during July 2004, and it is concluded that the temporal and spatial figures of absolute VSWV and relative VSWV can be useful in monitoring the evolution of water vapor field and be potential in better understanding the precipitation process.