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1.
随着空间大地测量技术观测精度的提高 ,需要激光测距理论模型适应目前和未来可预见的精度要求 .本文基于激光测距的基本原理 ,给出了太阳系质心参考系 (BRS)和地球质心参考系 (GRS)中的相对论激光测距的理论模型 ,对两种激光测距模型中有关引力时延的量级进行了估计 ,并给出了完整而自洽的时间尺度和时空坐标变换的理论公式 .根据最新的BRS和GRS系之间的时空坐标变换关系 ,在皮秒 (10 - 1 2 s)的精度下 ,推导出了在GRS中适合于所有激光测距问题的相对论模型 ,同时扩展了IERS推荐的激光测距模型的适用范围 相似文献
2.
中性大气折射延迟是激光测距技术的主要误差源.本文基于国际大地测量与地球物理联合会（IUGG）1999决议推荐的光学和近红外波段的大气折射率差理论模型,在Mendes（2004）理论的基础上,对某些理论公式进行了重新推导,给出了大气折射率差静力学和非静力学分量的实用表达式.推导出了大气折射率差的级数展开式,并保留至波长的负6次方项;同时在水气引起的折射率差上加上了频率改正项.计算发现,水气项中的频率改正对折射率差的贡献是不可忽略的.本文工作可为空间大地测量,特别是激光测距技术的研究提供一定的参考和依据. 相似文献
3.
The determination of the local gravity field by means of the point mass inversion method can be performed as an alternative to conventional numerical methods, such as the least-squares collocation. Based on the first derivative of the inverse-distance Newtonian potential for the representation of the gravity anomaly data, it is possible to compute any wavelength component of the geoid in planar approximation with sufficient accuracy. In order to exemplify the theoretical concept, two applications are presented of the computation of two different wavelength components of the geoid, the long wavelength component in a local solution and the short wavelength component in a regional solution. The results are compared with corresponding least-squares collocation solutions, using a global geopotential model to remove and to restore the long wavelength component. 相似文献
4.
Glonass Laser Ranging Accuracy With Satellite Signature Effect 总被引：1，自引：0，他引：1
GLONASS satellites have been tracked by the worldwide laser ranging networkas well as by the GLONASS-borne microwave-based technique. Owing to thelarge size of their corner cube reflector arrays, the amount of ranging data is enough to determine their orbits from laser ranging data alone. We found, however, that the large size of the array affected the accuracy of measurement to an extent that is dependent on the characteristics of the ranging systems. An azimuthal variation of the reflector array response was also detected in observations from single-photon laser ranging. Orbital analysis reveals that the effect makes the measured range on average 22 mm shorter than expected in the absence of the large array, which explains more than half of the offset of 39 mm previously discovered between microwave and laser orbits. 相似文献
5.
Fluid flow in many hydrocarbon reservoirs is controlled by aligned fractures which make the medium anisotropic on the scale of seismic wavelength. Applying the linear‐slip theory, we investigate seismic signatures of the effective medium produced by a single set of ‘general’ vertical fractures embedded in a purely isotropic host rock. The generality of our fracture model means the allowance for coupling between the normal (to the fracture plane) stress and the tangential jump in displacement (and vice versa). Despite its low (triclinic) symmetry, the medium is described by just nine independent effective parameters and possesses several distinct features which help to identify the physical model and estimate the fracture compliances and background velocities. For example, the polarization vector of the vertically propagating fast shear wave S1 and the semi‐major axis of the S1‐wave normal‐moveout (NMO) ellipse from a horizontal reflector always point in the direction of the fracture strike. Moreover, for the S1‐wave both the vertical velocity and the NMO velocity along the fractures are equal to the shear‐wave velocity in the host rock. Analysis of seismic signatures in the limit of small fracture weaknesses allows us to select the input data needed for unambiguous fracture characterization. The fracture and background parameters can be estimated using the NMO ellipses from horizontal reflectors and vertical velocities of P‐waves and two split S‐waves, combined with a portion of the P‐wave slowness surface reconstructed from multi‐azimuth walkaway vertical seismic profiling (VSP) data. The stability of the parameter‐estimation procedure is verified by performing non‐linear inversion based on the exact equations. 相似文献
6.
Histogram and variogram inference in the multigaussian model 总被引：1，自引：4，他引：1
Xavier Emery Julián M. Ortiz 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(1):48-58
Several iterative algorithms are proposed to improve the histogram and variogram inference in the framework of the multigaussian model. The starting point is the variogram obtained after a traditional normal score transform. The subsequent step consists in simulating many sets of gaussian values with this variogram at the data locations, so that the ranking of the original values is honored. The expected gaussian transformation and the expected variogram are computed by an averaging operation over the simulated datasets. The variogram model is then updated and the procedure is repeated until convergence. Such an iterative algorithm can adapt to the case of tied data and despike the histogram. Two additional issues are also examined, referred to the modeling of the empirical transformation function and to the optimal pair weighting when computing the sample variogram. 相似文献
7.
利用SH地震波（偏振化方向垂直入射面的横波）在地层界面反射系数的附加相角导出了SH波Goos-Hänchen效应所引起的横向偏移和横向偏移渡越时间,给出了Goos-Hänchen效应正常时差公式,讨论了Goos-Hänchen效应对反射SH波正常时差的影响,绘出了横向偏移、横向偏移渡越时间、Goos-Hänchen效应正常时差及Goos-Hänchen效应正常时差校正量曲线.数值算例表明：对掠入射波或入射角在临界角附近的入射波,SH反射波的横向偏移、横向偏移渡越时间非常大,Goos-Hänchen效应对正常时差会产生较大的测量误差,在其他角度的入射波,横向偏移（横向偏移渡越时间）与波长（周期）为同一个数量级.横向偏移效应对SH反射波的传播走时影响是不可忽略的,因此在实际的地震资料处理中应进行横向偏移效应误差校正. 相似文献
8.
Resolution analysis of geophysical images: Comparison between point spread function and region of data influence measures 总被引：1，自引：0，他引：1
Practical decisions are often made based on the subsurface images obtained by inverting geophysical data. Therefore it is important to understand the resolution of the image, which is a function of several factors, including the underlying geophysical experiment, noise in the data, prior information and the ability to model the physics appropriately. An important step towards interpreting the image is to quantify how much of the solution is required to satisfy the data observations and how much exists solely due to the prior information used to stabilize the solution. A procedure to identify the regions that are not constrained by the data would help when interpreting the image. For linear inverse problems this procedure is well established, but for non‐linear problems the procedure is more complicated. In this paper we compare two different approaches to resolution analysis of geophysical images: the region of data influence index and a resolution spread computed using point spread functions. The region of data influence method is a fully non‐linear approach, while the point spread function analysis is a linearized approach. An approximate relationship between the region of data influence and the resolution matrix is derived, which suggests that the region of data influence is connected with the rows of the resolution matrix. The point‐spread‐function spread measure is connected with the columns of the resolution matrix, and therefore the point‐spread‐function spread and the region of data influence are fundamentally different resolution measures. From a practical point of view, if two different approaches indicate similar interpretations on post‐inversion images, the confidence in the interpretation is enhanced. We demonstrate the use of the two approaches on a linear synthetic example and a non‐linear synthetic example, and apply them to a non‐linear electromagnetic field data example. 相似文献
9.
Rayleigh-wave phase velocities have been utilized to determine shear (S)-wave velocities in near-surface geophysics since early 1980s. One of the key steps is to calculate theoretical dispersion curves of an earth model. When the S-wave velocity of the surface layer is higher than some of the layers below, however, the Rayleigh-wave phase velocity in a high-frequency range calculated by existing algorithms approaches the lowest S-wave velocity among the layers above the half-space, rather than a value related to the S-wave velocity of the surface layer. According to our numerical modeling results based on wave equation, trends of the Rayleigh-wave dispersive energy approach about a 91% of the S-wave velocity of the surface layer at a high-frequency range when its wavelength is much shorter than the thickness of the surface layer, which cannot be fitted by a dispersion curve calculated by existing algorithms. We propose a method to calculate Rayleigh-wave phase velocities of models with a high-velocity surface layer by considering its penetration depth. We build a substituted model that only contains the layer with the lowest S-wave velocity among the layers above the half-space and the layers above it. We use the substituted model to replace the original model to calculate phase velocities when the Rayleigh-wave wavelength is not long enough to penetrate the lowest S-wave velocity layer. Several synthetic models are used to verify fitness between the dispersion curve calculated by our proposed method and the trend of the highest dispersive energy. Examples of inversion also demonstrate high accuracy of using our method as the forward calculation method during the inversions. 相似文献
10.
Frequency-dependent amplitude variation with offset offers an effective method for hydrocarbon detections and analysis of fluid flow during production of oil and natural gas within a fractured reservoir. An appropriate representation for the frequency dependency of seismic amplitude variation with offset signatures should incorporate influences of dispersive and attenuating properties of a reservoir and the layered structure for either isotropic or anisotropic dispersion analysis. In this study, we use an equivalent medium permeated with aligned fractures that simulates frequency-dependent anisotropy, which is sensitive to the filled fluid of fractures. The model, where pores and fractures are filled with two different fluids, considers velocity dispersion and attenuation due to mesoscopic wave-induced fluid flow. We have introduced an improved scheme seamlessly linking rock physics modelling and calculations for frequency-dependent reflection coefficients based on the propagator matrix technique. The modelling scheme is performed in the frequency-slowness domain and can properly incorporate effects of both bedded structure of the reservoir and velocity dispersion quantified with frequency-dependent stiffness. Therefore, for a dispersive and attenuated layered model, seismic signatures represent a combined contribution of impedance contrast, layer thickness, anisotropic dispersion of the fractured media and tuning and interference of thin layers, which has been avoided by current conventional methods. Frequency-dependent amplitude variation with offset responses was studied via considering the influences of fracture fills, layer thicknesses and fracture weaknesses for three classes amplitude variation with offset reservoirs. Modelling results show the applicability of the introduced procedure for interpretations of frequency-dependent seismic anomalies associated with both layered structure and velocity dispersion of an equivalent anisotropic medium. The implications indicate that anisotropic velocity dispersion should be incorporated accurately to obtain enhanced amplitude variation with offset interpretations. The presented frequency-dependent amplitude variation with offset modelling procedure offers a useful tool for fracture fluid detections in an anisotropic dispersive reservoir with layered structures. 相似文献
11.
Decomposing seismic data in local slopes is the basic idea behind velocity‐independent imaging. Using accurate moveout approximations enables computing moveout attributes such as normal moveout velocity and nonhyperbolic parameters as functions of zero‐offset travel time. Mapping of moveout attributes is performed from the pre‐stack seismic data domain into the time‐migrated image domain. The different moveout attributes have different accuracy for a given moveout approximation that depends on the corresponding order of travel‐time derivative. The most accurate attribute is the zero‐offset travel time, and the nonhyperbolic parameter has the worst accuracy, regardless of the moveout approximation. Typically, the mapping of moveout attributes is performed using a point‐to‐point procedure, whereas the generalized moveout approximation requires two point‐to‐point mappings. Testing the attribute mapping on the different models shows that the accuracy of mapped attributes is model dependent, whereas the generalized moveout approximation gives practically exact results. 相似文献
12.
Long‐range terrestrial laser scanning for geomorphological change detection in alpine terrain – handling uncertainties 
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下载免费PDF全文 Long‐range terrestrial laser scanning (TLS) is an emerging method for the monitoring of alpine slopes in the vicinity of infrastructure. Nevertheless, deformation monitoring of alpine natural terrain is difficult and becomes even more challenging with larger scan distances. In this study we present approaches for the handling of spatially variable measurement uncertainties in the context of geomorphological change detection using multi‐temporal data sets. A robust distance measurement is developed, which deals with surface roughness and areas of lower point densities. The level of detection (LOD), i.e. the threshold distinguishing between real surface change and data noise, is based on a confidence interval considering the spatial variability of TLS errors caused by large laser footprints, low incidence angles and surface roughness. Spatially variable positional uncertainties are modelled for each point according to its range and the object geometry hit. The local point cloud roughness is estimated in the distance calculation process from the variance of least‐squares fitted planes. Distance calculation and LOD assessment are applied in two study areas in the Eastern Alps (Austria) using multi‐temporal laser scanning data sets of slopes surrounding reservoir lakes. At Finstertal, two TLS point clouds of high alpine terrain and scanned from ranges between 300 and 1800 m are compared. At Gepatsch, the comparison is done between an airborne laser scanning (ALS) and a TLS point cloud of a vegetated mountain slope scanned from ranges between 600 and 3600 m. Although these data sets feature different conditions regarding the scan setup and the surface conditions, the presented approach makes it possible to reliably analyse the geomorphological activity. This includes the automatic detection of rock glacier movement, rockfall and debris slides, even in areas where a difference in vegetation cover could be observed. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
13.
The variation in point precipitation with elevation is investigated using an event-based stochastic model of thunderstorm rainfall and empirical data. Parameters of the model correspond to the number of events per unit of time and the depth of rainfall per event. An increase in precipitation with elevation may be due to an increase in the number of events, in the amount of rainfall per event or to some combination of both possibilities. The distribution of the number of events per season is assumed to be a Poisson variate while the distribution of point rainfall depths may be taken as geometric. The summation of a random number of random variables is used to represent seasonal point precipitation. Assuming that the two parameters of the model increase linearly with elevation, then total seasonal rainfall increases as a quadratic polynomial with elevation. The use of the model allows one to obtain the return period of storm rainfall of a given magnitude despite a short historical record. An independent set of data was used to verify the procedure. 相似文献
14.
对流层延迟是全球导航卫星系统(Global Navigation Satellite System,GNSS)导航定位中的重要误差源,其量值主要受气象条件影响.采用传统对流层建模思路,利用GPT2模型来提供相对准确的气温、气压和相对湿度,然后利用Saastamoinen模型来计算天顶对流层延迟,由此构建了GPT2+Saas模型;采用新的对流层建模思路,直接针对天顶对流层延迟的时空特性建模,构建了与GPT2+Saas模型相匹配的GZTDS格网模型.以GGOS Atmosphere格网数据为参考,GPT2+Saas模型(Bias:0.2cm;RMS:4.2cm)和GZTDS模型(Bias:0.2cm;RMS:3.7cm)较UNB3m模型精度分别提升34%和43%.以IGS(International GNSS Service)数据为参考,GPT2+Saas(Bias:0.5cm;RMS:4.7cm)和GZTDS(Bias:-0.3cm;RMS:3.8cm)相对UNB3m模型精度分别提升10%和27%.针对GPT2+Saas模型在少数测站出现精度异常的情况进行了研究,探讨了可能的原因.在两种不同思路构建的精化对流层模型中,GZTDS模型不仅表现出更高的精度,而且在时间稳定性和地理稳定性上也表现出优越性. 相似文献
15.
The present study describes a new system designed and developed for observing crustal deformation on the sea floor. The system consists of two parts, the kinematic positioning by global positioning system (GPS) and acoustic ranging techniques. Since the location of a site at the ocean bottom relative to a reference site on land cannot be determined directly, the procedure was divided into two steps. First, the position of a vessel was determined using differential and kinematic GPS techniques, and then the position of a reference point at the ocean bottom was located relative to the vessel using the acoustic ranging technique. Thus, the location of the ocean-bottom station is determined relative to the reference sites on land in the global reference system. The accuracy was tested in several ways. In one experiment, a buoy was used as the surface station which linked the positions of a GPS receiver to the acoustic transponder. Assuming a simple sound velocity profile of the seawater, the position of an ocean-bottom reference point was estimated with an accuracy of several meters. Thus, with the present system, it is difficult to observe ocean-bottom crustal deformations generated by typical plate motions. Methods are being investigated to improve the observation system for more accurate sea floor positioning. 相似文献
16.
A neural network approach for the real-time detection of faults 总被引：2，自引：2，他引：0
Fault detection is an essential part of the operation of any chemical plant. Early detection of faults is important in chemical
industry since a lot of damage and loss can result before a fault present in the system is detected. Even though fault detection
algorithms are designed and implemented for quickly detecting incidents, most these algorithms do not have an optimal property
in terms of detection delay with respect to false alarm rate. Based on the optimization property of cumulative sum (CUSUM),
a real-time system for detecting changes in dynamic systems is designed in this paper. This work is motivated by combining
two fault detection (FD) strategies; a simplified procedure of the incident detection problem is formulated by using both
the artificial neural networks (ANN) and the CUSUM statistical test (Page–Hinkley test). The design of a model-based residual
generator is intended to reveal any drift from the normal behavior of the process. In order to obtain a reliable model for
the normal process dynamics, the neural black-box modeling by means of a nonlinear auto-regressive with eXogenous input (NARX)
model has been chosen in this study. This paper also shows the choice and the performance of the neural network in the training
and test phases. After describing the system architecture and the proposed methodology of the fault detection, we present
a realistic application in order to show the technique’s potential. The purpose is to develop and test the fault detection
method on a real incident data, to detect the change presence, and pinpoint the moment it occurred. The experimental results
demonstrate the robustness of the FD method. 相似文献
17.
Digital elevation models derived from airborne laser scanning point clouds: appropriate spatial resolutions for multi‐temporal characterization and quantification of geomorphological processes 下载免费PDF全文
下载免费PDF全文 Digital terrain models (DTMs) are a standard data source for a variety of applications. DTM differencing is also widely used for detection and quantification of topographic changes. While several investigations have been made on the accuracy of DTMs, calculated from different kinds of input data, little has been published on the error of DTM differencing, specifically for the quantification of geomorphological processes. In this study, an extensive, multi‐temporal set of airborne laser scanning (ALS) data is used to investigate the accuracy of topographic change calculations in a high alpine environment, caused by different geomorphic processes. Differences from DTMs with cell sizes ranging from 0.25 m to 10 m were calculated and compared to very accurate point‐to‐point calculations for a variety of processes and in nearby stable areas which show no significant surface changes. The representativeness of the DTM differences is then compared to the terrain slope and surface roughness of the investigated areas to show the influence of these parameters on the errors in the differences. Those errors are then taken into account for analyses of the applicability of different cell sizes for the investigation of geomorphic processes with different magnitudes and over different time periods. The analyses show that the error of DTM differences increases with lower point densities and higher roughness and slope values. The higher the error, the greater the differences between two elevation datasets have to be in order to quantify certain morphodynamic processes. Lower point densities and higher roughness and slope values require greater process rates or longer time intervals in order to obtain valid results. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
18.
Differences between traveltimes from sonic to seismic frequencies, commonly known as drift, can be attributed to a combination of multiple scattering and absorption. The portion due to scattering can be estimated directly by calculating synthetic seismograms from sonic logs. A simple alternative approach is suggested by the long-wave equivalent averaging formulae for the effective elastic properties of a stack of thin layers, which gives the same traveltime delays as the low-frequency limit of the scattering dispersion. We consider the application of these averaging formulae over a frequency-dependent window with the hope of extending their use to frequencies higher than those allowed by the original validity conditions. However, comparison of the time delay due to window-averaging with the scattering dispersion predicted by the O'Doherty-Anstey formula reveals that it is not possible to specify a form of window that will fit the dispersion across the spectrum for arbitrary log statistics. A window with a width proportional to the wavelength squared matches the behaviour at the low-frequency end of the dispersive range for most logs, and allows an almost exact match of the drift across the entire spectrum for exponential correlation functions. We examine a real log, taken from a hole in nearly plane-layered geology, which displays strong quasi-cyclical variations on one scale as well as more random, smaller-scale fluctuations. The details of its drift behaviour are studied using simple models of the gross features. The form of window which gave a good theoretical fit to the dispersion for an exponential log correlation function can only fit the computed drift at high or low frequencies, confirming that there are at least two significant scale-lengths of fluctuation. A better overall fit is obtained for a window whose width is proportional to the wavelength. The calculated scattering drift is significantly less than that observed from a vertical seismic profile, but the difference cannot be wholly ascribed to absorption. This is because the source frequency of the sonic tool is not appropriate for its resolution (receiver spacing) so that the scattering drift from sonic to seismic frequencies cannot be fully estimated from the layer model derived from the log. 相似文献
19.
传统二维震害图像方法对震后区域进行研究时,由于其拍摄角度具有局限性,震后区域图像的视觉效果不理想。提出基于三维激光扫描技术的震后区域三维虚拟重建方法,采用三维激光扫描仪测量震后区域,获取该区域的点云数据,采用Cyclone软件合并点云数据后,得到震后区域拼接后的整体点云图,将该图点云数据进行去体外孤点、去噪声点以及点云取样等处理后实施封装,在封装的点云数据上采用Sketch模型实施贴图操作,实现视觉传达效果理想的震后区域三维图形的虚拟重建。实验证明,所提方法对震后区域的三维图像虚拟重建结果精度高、视觉效果好。 相似文献
20.
The objective of moveout parameter inversion is to derive sets of parameter models that can be used for moveout correction and stacking at each common midpoint location to increase the signal-to-noise ratio of the data and to provide insights into the kinematic characteristics of the data amongst other things. In this paper, we introduce a data-driven user-constrained optimization scheme that utilizes manual picks at a point on each reflector within a common midpoint gather to constrain the search space in which an optimization procedure can search for the optimal parameter sets at each reflection. The picks are used to create boundary curves which can be derived approximately via an optimization technique or analytically via the derivation of an analytical bounds function. In this paper, we derive analytical forms of bounds functions for four different moveout cases. These are normal moveout, non-hyperbolic moveout, azimuthally dependent normal moveout and azimuthally dependent non-hyperbolic moveout. The optimization procedure utilized here to search for the optimal moveout parameters is the particle swarm optimization technique. However, any metaheuristic optimization procedure could be modified to account for the constraints introduced in this paper. The technique is tested on two-layer synthetic models based on three of the four moveout cases discussed in this paper. It is also applied to an elastic forward modelled synthetic model called the HESS model, and finally to real 2D land data from Alaska. The resultant stacks show a marked improvement in the signal-to-noise ratio compared to the raw stacks. The results for the normal moveout, non-hyperbolic moveout and azimuthally dependent normal moveout tests suggest that the method is viable for said models. Results demonstrate that our method offers potential as an alternative to conventional parameter picking and inversion schemes, particularly for some cases where the number of parameters in the moveout approximation is 2 or greater. 相似文献