时域有限差分法在地质雷达二维正演模拟中的应用   总被引：11，自引：4，他引：7  

戴前伟  冯德山  王启龙  何继善 《地球物理学进展》2004,19(4):898-902

本文从地质雷达正演原理着手,分析了差分格式中半空间步长与半时间步长的实现方法,同时通过分析数值频散的产生,进而推导出了理想频散关系和超吸收边界条件．最后文中还对比了有无边界条件的雷达正演模拟效果和精度．  相似文献   

Observation and Research of the Transits of Extrasolar Planets     

Ji-Cheng Zhang  Chen Cao  Nan Song  Fei-Ge Wang  Xiao-Tong Zhang 《Chinese Astronomy and Astrophysics》2011,35(4):409

In order to make more accurate estimates of the physical parameters of extrasolar planets, the observation and research on the phenomena of transits of the 7 known stars with the planetary systems TrES-1, TrES-3, XO-2, WASP-1, WASP-2, WASP-3 and HAT-P-7 are carried out with the 1-m reflecting telescope at Shandong University Weihai Astronomical Observatory/Weihai Municipal Astronomical Observatory. The fundamental conditions of the observation and data processing are introduced, and the transit light curves as well as the parameters of some planets derived from them are given. At the same time, when the results are summarized and analyzed, the prospects for the more in-depth and detailed researches which will be further carried out are also described.  相似文献   

Rest‐frame UV to optical X‐shooter spectrum of the gravitationally lensed galaxy “the 8 o'clock arc”: Dissection of its physical properties     

M. Dessauges‐Zavadsky  S. D'Odorico  L. Christensen  D. Schaerer  J. Richard 《Astronomische Nachrichten》2011,332(3):307-308

We present the rest‐frame UV to optical spectrum of the gravitationally lensed galaxy, the “8 o'clock arc” at z = 2.735, obtained with the X‐shooter spectrograph. This is one of the rare comprehensive study of a high‐redshift star‐forming galaxy, usually not feasible due to the faintness of these objects. The spectrum of the 8 o'clock arc is rich in stellar and interstellar absorption features and in nebular emission features. Their analysis allowed us to derive most of the physical properties characterizing the galaxy. From HST images, we reconstruct the morphology of the arc in the source plane and confirm that we resolve a clump in rotation around the main core of galaxy in our X‐shooter spectrum (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

The satellite reversion of dissolved organic carbon (DOC) based on the analysis of the mixing behavior of DOC and colored dissolved organic matter: the East China Sea as an example     

LIU Qiong  PAN Delu  BAI Yan  WU Kai  CHEN Chen-Tung Arthur  SUN Jun  ZHANG Lin 《海洋学报(英文版)》2013,32(2)

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Jason-1 Precision Orbit Determination by Combining SLR and DORIS with GPS Tracking Data     

KEY-ROK CHOI  JOHN C. RIES  BYRON D. TAPLEY 《Marine Geodesy》2013,36(1-2):319-331

With the implementation of the Jason-1 satellite altimeter mission, the goal of reaching the 1-cm level in orbit accuracy was set. To support the Precision Orbit Determination (POD) requirements, the Jason-1 spacecraft carries receivers for DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) and GPS (Global Positioning System), as well as a retroreflector for SLR (Satellite Laser Ranging). The overall orbit accuracy for Jason will depend on the quality and the relative weighting of the available tracking data. In this study, the relative importance of the SLR, DORIS, and GPS tracking data is assessed along with the most effective parameterization for accounting for the unmodeled accelerations through the application of empirical accelerations. The optimal relative weighting for each type of tracking data was examined. It is demonstrated that GPS tracking alone is capable of supporting a radial orbit accuracy for Jason-1 at the 1-cm level, and that including SLR tracking provides additional benefits. It is also shown that the GRACE (Gravity Recovery and Climate Experiment) gravity model GGM01S provides a significant improvement in the orbit accuracy and reduction in the level of geographically correlated orbit errors.  相似文献   

Impact of Ocean Mean Dynamic Topography on Satellite Data Assimilation     

F. BIROL  J. M. BRANKART  F. CASTRUCCIO  P. BRASSEUR  J. VERRON 《Marine Geodesy》2013,36(1-2):59-78

The response of an eddy-permitting ocean model to changes imposed by the use of different mean dynamic topographies (MDT) is analyzed in a multivariate assimilation context, allowing the evaluation of this impact, not only on the surface circulation, but also on the interior ocean representation. The assimilation scheme is a reduced-order sequential Kalman filter (SEEK). In a first set of experiments, high resolution sea surface temperature, along-track sea surface height and sea surface salinity from climatology are assimilated into a 1/3° resolution North and Tropical Atlantic version of the HYCOM model. In a second experiment, in situ profile data are assimilated in addition to the surface measurements.

The first set of experiments illustrates that important differences in the representation of the horizontal model circulation pattern are related to differences in the MDT used. The objective of assimilation is to improve the representation of the 3D ocean state. However, the imperfect representation of the mean dynamic topography appears to be an important limiting factor with regard to the degree of realism obtained in the simulated flow.

Vertical temperature and salinity profiles are key observations to drive a general circulation ocean model toward a more realistic state. The second set of experiments shows that assimilating them in addition to sea surface measurements is a far from trivial exercise. A specific difficulty is due to inconsistencies between the dynamic topography diagnosed from in situ observations and that diagnosed from sea surface height. These two fields obtained from different data sources do not contain exactly the same information. In order to overcome this difficulty, a strategy is proposed and validated.  相似文献   

Accuracy Assessment of the TOPEX/Poseidon Ionosphere Measurements     

CHANGYIN ZHAO  C. K. SHUM  YUCHAN YI  SHENGJIE GE  DIETER BILITZA  PHILIP CALLAHAN 《Marine Geodesy》2013,36(3-4):729-739

We conducted an assessment of the TOPEX dual-frequency nadir ionosphere observations in the TOPEX/Poseidon (T/P) GDR by comparing TOPEX with the Center for Orbit Determination in Europe (CODE) Global Ionosphere Map (GIM), the climatological model IRI2001, and the DORIS (onboard T/P) relative ionosphere delays. We investigated the TOPEX (TOPEX Side A and TOPEX Side B altimeters, TSA and TSB, respectively) ionosphere observations for the time period 1995–2001, covering periods of low, intermediate, and high solar activity. Here, we use absolute path delays (at Ku-band frequency of the TOPEX altimeter and with positive signs) rather than Total Electron Content (TEC). We found significant biases between GIM and TOPEX (GIM–TOPEX) nadir ionosphere path delays: ?8.1 ± 0.4 {mm} formal uncertainties and equivalent to 3.7 TECu) and ?9.0 ± 0.7 {mm} (4.1 TECu) for TSA and TSB, respectively, indicating that the TOPEX path delay is longer (or with higher TECu) than GIM. The estimated relative biases vary with latitude and with daytime or nighttime passes. The estimated biases in the path delays (DORIS–TOPEX) are: ?10.9 ± 0.4 {mm} (5.0 TECu) and ?14.8 ± 0.6 {mm} (6.7 TECu), for TSA and TSB, respectively. There is a distinct jump of the DORIS path delays (?3.9 ± 0.7 {mm}, TSA delays longer than TSB delays) at the TSB altimeter switch in February 1999, presumably due to inconsistent DORIS processing. The origin of the bias between GIM (GPS, L-band) and TOPEX (radar altimeter, Ku-band) is currently unknown and warrants further investigation. Finally, the estimated drift rates between GIM and TSA, DORIS and TSA ionosphere path delays for the 6-year study span are ?0.4 mm/yr and ?0.8 mm/yr, respectively, providing a possible error bound for the TOPEX/Poseidon sea level observations during periods of low and intermediate solar activity.  相似文献   

Towards a Seamless Transition from TOPEX/Poseidon to Jason-1     

B. D. BECKLEY  N. P. ZELENSKY  S. B. LUTHCKE  P. S. CALLAHAN 《Marine Geodesy》2013,36(3-4):373-389

The Jason-1 verification phase has proven to be a unique and successful calibration experiment to quantify the agreement with its predecessor TOPEX/Poseidon. Although both missions have met prescribed error budgets, comparison of the mean and time-varying sea surface height profiles from near simultaneous observations derived from the missions' Geophysical Data Records exhibit significant basin scale differences. Several suspected sources causing this disagreement are identified and improved upon, including (a) replacement of TOPEX and Jason project POE with enhanced orbits computed at GSFC within a consistent ITRF2000 terrestrial reference frame, (b) application of waveform retracking corrections to TOPEX significant wave height and sea surface heights, (c) resultant improved efficacy of the TOPEX sea state bias estimation from the value added sea surface height, and (d) estimation of Jason-1 sea state bias employing dual TOPEX/Jason crossover and collinear sea surface height residuals unique to the validation mission. The resultant mean sea surface height comparison shows improved agreement at better than 60 percent level of variance reduction with a standard deviation less then 0.5 cm.  相似文献   

Altimeter Signal-to-Noise for Deep Ocean Processes in Operational Systems     

KIRK R. WHITMER  GREGG A. JACOBS  OLE MARTIN SMEDSTAD 《Marine Geodesy》2013,36(3-4):433-451

The ocean signal for this study is the sea surface height due to the slowly varying (greater than 5-day) ocean processes, which are predominantly the deep ocean mesoscale. These processes are the focus of present assimilation systems for monitoring and predicting ocean circulation due to ocean fronts and eddies and the associated environmental changes that impact real time activities in areas with depths greater than about 200 m. By this definition, signal-to-noise may be estimated directly from altimeter data sets through a crossover point analysis. The RMS variability in crossover differences is due to instrument noise, errors in environmental corrections to the satellite observation, and short time period oceanic variations. The signal-to-noise ratio indicates that shallow areas are typically not well observed due to the high frequency fluctuations. Many deep ocean areas also contain significant high frequency variability such as the subpolar latitudes, which have large atmospheric pressure systems moving through, and these in turn generate large errors in the inverse barometer correction. Understanding the spatial variations of signal to noise is a necessary prerequisite for correct assimilation of the data into operational systems.  相似文献   

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

BRUCE HAINES  YOAZ BAR-SEVER  WILLY BERTIGER  SHAILEN DESAI  PASCAL WILLIS 《Marine Geodesy》2013,36(1-2):299-318

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.  相似文献