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1.
本文将Tikhonov正则化方法与active-set算法相结合,利用双频电磁波电导率成像原理,求解其反演成像方程.不仅对现有算法进行了改进,也促进了算法的实际应用.本文研究了在双频电磁波电导率成像方程建立后,如何根据其严重病态性质,选择合适的算法求解矩阵成像方程.针对电导率非负的特性,引入正则化参数,将问题转化为一个非负最小二乘问题,并用active-set算法求解.采用改进后的迭代算法对理论模型进行了数值模拟计算,验证了该方法的有效性.应用到实际电导率成像反演,与常规的LSQR、SP-LSQR、Tikhonov正则化等算法进行比较,取得了满意的结果. 相似文献
2.
利用加速差分进化算法反演非均匀介质电磁成像 总被引：1，自引：1，他引：0
本文研究了差分进化算法在地球物理反演中的几种应用.利用双频电磁波电导率成像原理建立成像方程后,根据其严重病态性质,将Tikhonov正则化方法与差分进化算法结合,反演其成像方程.为加速差分进化算法的收敛速度,提出了将种群熵的自适应差分进化(ARDE)算法以及粒子群差分进化混合(PSODE)算法分别与Tikhonov正则化方法结合.在大型反演计算中,这两种方法可以在不影响反演效果的前提下,不同程度地提高收敛速度,降低时间成本.适宜于在正则化参数选取困难情况时的地球物理反演问题的求解. 相似文献
3.
本文针对工程建筑中的混凝土无损探测问题,提出了一种新的反演成像方法.它避免了传统方法观察偏移探测数据的情况.这种方法以探地雷达为探测手段,以电磁场原理为理论依据,其结果更具定量化和可视性.具体算法是将阻尼高斯牛顿法和GCV方法(Generalized Cross Validation)结合起来,其中阻尼牛顿法可以避免传统牛顿法计算Hessian矩阵的困难,GCV方法可以自适应地选择正则化参数,既减小了计算量又克服了噪声及不适定性的影响.数值算例验证了算法的有效性. 相似文献
4.
对于多孔介质中发生物理化学反应的溶质运移现象,可以用带有非线性源（汇）项作用的一维对流弥散-反应扩散方程来描述,但方程中反映溶质吸附/解吸附能力的源(汇)项系数往往是未知的. 本文讨论了基于出流端浓度观测数据的源项系数反演问题. 根据Tikhonov正则化和矩阵的奇异值分解系统,建立了一种离散的迭代正则化算法,给出了算法实现步骤.数值模拟结果表明该算法不仅精度高,而且对于数据的随机扰动具有稳定性.最后应用建立的算法反演计算了一个具体的土柱试验源项系数,数值结果也表明文中所构造算法的有效性. 相似文献
5.
有别于传统基于梯度信息的反演方法在正则化约束中用总梯度逼近海塞逆矩阵的技术,本文将正则化约束问题的数据拟合项和模型光滑项分开考虑,只利用数据拟合函数的梯度信息对数据拟合项的海塞矩阵进行逼近,通过求解类高斯牛顿下降方向方程得到不依赖前几次迭代正则化因子的更精确下降方向,在求解当前迭代下降方向的过程中,通过保证右端项中两个向量的二范数在同一数量级的原则,实现了正则化因子的自动更新.对理论模型的试算表明这种自适应正则化反演方案可以在拟牛顿反演框架下基本达到OCCAM的算法稳定性,反演结果对初始模型依赖性较小,同时又无需在一次迭代中多次搜索最佳正则化因子.本文还基于此算法讨论了大地电磁各参数对于反演结果的影响,由于本文的反演结果能得到充分的正则化约束,因而在此框架下讨论阻抗和倾子在反演中的作用相对更为客观. 相似文献
6.
7.
本文针对水利水电工程中的混凝土构件无损探测问题,提出了一种新的反演成像方法.传统方法主要依赖人工经验观察偏移探测数据,精度无法保证.这种方法以Maxwell方程的TM问题为数学模型,在混凝土的表面放置发射源与接收器,根据探地雷达的接收数据,采用同伦优化方法结合收敛速度较快的阻尼高斯牛顿方法作为反演算法,其成像结果更具定量化和可视性.该成像方法克服了传统雷达剖面图只能近似地反映混凝土中埋藏物及缺陷的深度、大小等缺点,不仅能够探测混凝土内部异物的位置,而且能够比较准确地确定异物的大小及属性.通过计算机模拟以及对实际资料的处理,验证了该反演成像结果直观、可靠、具有一定的应用价值. 相似文献
8.
高频天波返回散射探测作为重要的电离层探测手段,能够实现遥远区域电离层空间上的连续监测,探测获取的返回散射扫频电离图显示了探测频率-群路径-回波能量三者之间的关系.由于电离图包含了探测路径上的电离层状态信息,通过对其反演可以实时获取大面积范围的电离层参数.本文提出了一种基于解空间约束的返回散射前沿反演算法,能够重构电离层水平不均匀结构.针对反演非线性问题,采用Newton-Kontorovich方法进行求解,同时又引入了求解不适定问题的Tikhonov正则化方法,有益于解的稳定性和唯一性.利用模拟数据和实测数据分别对本文建立的算法进行了验证,并与Fridman和Fridman于1994年提出的反演方法进行了对比.结果表明,本文算法反演结果稳定,对返回散射前沿判读误差不敏感,与Fridman和Fridman 1994年方法相比,本文方法对电离层局部精细结构反演更加准确,具有较高的反演精度.本文提出的算法不但能够反演白天和夜间这种电离层较平稳时期的电离层状态,而且对于日出/日落时段等电子浓度分布变化较快情形下的电离层,也有很好的反演效果,表明了该算法在处理复杂多变的实际探测的返回散射电离图中的应用价值. 相似文献
9.
本文针对蒸汽辅助重力泄油(SAGD)生产中开发监测问题,发展了综合应用地震及重力数据反演储层密度的联合反演算法.通过测井数据建立纵波阻抗与密度的直接关系,并推导出这种关系下重力与纵波阻抗数据联合反演的计算方法,从而计算出蒸汽腔体密度分布规律.文中应用密度反演后验约束正则化方法,采用Tikhonov正则化模型,通过波阻抗数据作为约束进行联合反演,在算法上提高了稳定性,同时得到较高的反演精度.文中对SAGD生产中的理论模型进行了方法试算,并分析了算法的误差,最终应用于SAGD生产的实际数据中,通过最终反演结果分析,该方法取得了很好的应用效果. 相似文献
10.
《应用地球物理》2016,(1)
常规多波联合反演采用Zoeppritz方程的近似式构建正演方程,反演过程中需要假定背景纵横波速度比为常数,其反演精度不高,稳定性不好。本文提出了一种基于精确Zoeppritz方程的多波联合反演方法,结合贝叶斯方法进行广义线性反演。本方法基于精确Zoeppritz方程构建正演方程,避免了近似式反演在大角度时引起的误差;利用贝叶斯方法引入模型参数的先验分布信息,作为反演的正则化项,降低了反演的不适定性;反演目标函数中引入低频软约束,稳定了反演低频结果,提高了反演的鲁棒性;在求解反演目标函数时,利用快速算法,降低了反演的运算量。经过模型试算,证明了该方法的优越性和抗噪性;并在实际资料的应用中证明了该方法的实用性和有效性。 相似文献
11.
Yukiharu Hisaki 《Ocean Dynamics》2016,66(9):1065-1085
The high-frequency (HF) radar inversion algorithm for spectrum estimation (HIAS) can estimate ocean wave directional spectra from both dual and single radar. Wave data from a dual radar and two single radars are compared with in situ observations. The agreement of the wave parameters estimated from the dual radar with those from in situ observations is the best of the three. In contrast, the agreement of the wave parameters estimated from the single radar in which no Doppler spectra are observed in the cell closest to the in situ observation point is the worst among the three. Wave data from the dual radar and the two single radars are compared. The comparison of the wave heights estimated from the single and dual radars shows that the area sampled by the Doppler spectra for the single radar is more critical than the number of Doppler spectra in terms of agreement with the dual-radar-estimated wave heights. In contrast, the comparison of the wave periods demonstrates that the number of Doppler spectra observed by the single radar is more critical for agreement of the wave periods than the area of the Doppler spectra. There is a bias directed to the radar position in the single radar estimated wave direction. 相似文献
12.
Wei Shen Klaus-Werner Gurgel George Voulgaris Thomas Schlick Detlef Stammer 《Ocean Dynamics》2012,62(1):105-121
Land-based high-frequency (HF) radars have the unique capability of continuously monitoring ocean surface environments at
ranges up to 200 km off the coast. They provide reliable data on ocean surface currents and under slightly stricter conditions
can also give information on ocean waves. Although extraction of wind direction is possible, estimation of wind speed poses
a challenge. Existing methods estimate wind speed indirectly from the radar derived ocean wave spectrum, which is estimated
from the second-order sidebands of the radar Doppler spectrum. The latter is extracted at shorter ranges compared with the
first-order signal, thus limiting the method to short distances. Given this limitation, we explore the possibility of deriving
wind speed from radar first-order backscatter signal. Two new methods are developed and presented that explore the relationship
between wind speed and wave generation at the Bragg frequency matching that of the radar. One of the methods utilizes the
absolute energy level of the radar first-order peaks while the second method uses the directional spreading of the wind generated
waves at the Bragg frequency. For both methods, artificial neural network analysis is performed to derive the interdependence
of the relevant parameters with wind speed. The first method is suitable for application only at single locations where in
situ data are available and the network has been trained for while the second method can also be used outside of the training
location on any point within the radar coverage area. Both methods require two or more radar sites and information on the
radio beam direction. The methods are verified with data collected in Fedje, Norway, and the Ligurian Sea, Italy using beam
forming HF WEllen RAdar (WERA) systems operated at 27.68 and 12.5 MHz, respectively. The results show that application of
either method requires wind speeds above a minimum value (lower limit). This limit is radar frequency dependent and is 2.5
and 4.0 m/s for 27.68 and 12.5 MHz, respectively. In addition, an upper limit is identified which is caused by wave energy
saturation at the Bragg wave frequency. Estimation of this limit took place through an evaluation of a year long database
of ocean spectra generated by a numerical model (third generation WAM). It was found to be at 9.0 and 11.0 m/s for 27.68 and
12.5 MHz, respectively. Above this saturation limit, conventional second-order methods have to be applied, which at this range
of wind speed no longer suffer from low signal-to-noise ratios. For use in operational systems, a hybrid of first- and second-order
methods is recommended. 相似文献
13.
Ocean wave imaging mechanism by imaging radar 总被引：1，自引：1，他引：0
HE Yijun 《中国科学D辑(英文版)》2000,43(6):587-595
Analytical representations of the high frequency spectra of ocean wave and its variation due to the variation of ocean surface
current are derived from the wave-number spectrum balance equation. The ocean surface imaging formulation of real aperture
radar (RAR) is given using electromagnetic wave backscattering theory of ocean surface and the modulations of ocean surface
winds, currents and their variations to RAR are described. A general representation of the phase modulation induced by the
ocean surface motion is derived according to standard synthetic aperture radar (SAR) imaging theory. The detectability of
ocean current and sea bottom topography by imaging radar is discussed. The results constitute the theoretical basis for detecting
ocean wave fields, ocean surface winds, ocean surface current fields, sea bottom topography, internal wave and so on. 相似文献
14.
Inversion of swell frequency from a 1-year HF radar dataset collected in Brittany (France) 总被引：1，自引：1，他引：0
This article presents long period ocean wave (swell) frequencies inverted from a 13-month dataset of high-frequency (HF) phased array radars and an assessment of these estimates by comparison with WAVEWATCH III model data. The method of swell frequency inversion from high-frequency radar sea echo Doppler spectra is described. Radar data were collected from a two-site HF Wellen Radar (WERA) radar system on the west coast of Brittany (France) operating at 12 MHz. A standard beam-forming processing technique has been used to obtain Doppler spectra of processed radar cells. Swell frequencies are obtained from the frequencies of particular spectral peaks of the second-order continuum in hourly averaged Doppler spectra. The data coverage of effective Doppler spectra considered for swell frequency estimates shows the influence of islands and shallow water effects. Swell estimates from both radar stations are in good agreement. The comparison of radar-derived results to WAVEWATCH III (WW3) estimates shows that radar measurements agree quite well with model results. The bias and standard deviation between two estimates are very small for swells with frequency less than 0.09 Hz (period >11 s), whereas radar estimates are generally lower than model estimates for shorter swells, along with higher standard deviation. Statistical analysis suggests that radar measurement uncertainty explains most of the difference between radar and model estimates. For each swell event, time series of frequency exhibits a quasi-linear frequency increase which is associated with the dispersive property of wave phase velocity. The use of swell frequency estimates from both radars on common radar cells only slightly increases the accuracy of swell frequency measurement. 相似文献
15.
R&#;hrs Johannes Christensen Kai H&#;kon Hole Lars Robert Brostr&#;m G&#;ran Drivdal Magnus Sundby Svein 《Ocean Dynamics》2012,62(10):1519-1533
Knowledge of upper ocean currents is needed for trajectory forecasts and is essential for search and rescue operations and oil spill mitigation. This paper addresses effects of surface waves on ocean currents and drifter trajectories using in situ observations. The data set includes colocated measurements of directional wave spectra from a wave rider buoy, ocean currents measured by acoustic Doppler current profilers (ADCPs), as well as data from two types of tracking buoys that sample the currents at two different depths. The ADCP measures the Eulerian current at one point, as modelled by an ocean general circulation model, while the tracking buoys are advected by the Lagrangian current that includes the wave-induced Stokes drift. Based on our observations, we assess the importance of two different wave effects: (a) forcing of the ocean current by wave-induced surface fluxes and the Coriolis–Stokes force, and (b) advection of surface drifters by wave motion, that is the Stokes drift. Recent theoretical developments provide a framework for including these wave effects in ocean model systems. The order of magnitude of the Stokes drift is the same as the Eulerian current judging from the available data. The wave-induced momentum and turbulent kinetic energy fluxes are estimated and shown to be significant. Similarly, the wave-induced Coriolis–Stokes force is significant over time scales related to the inertial period. Surface drifter trajectories were analysed and could be reproduced using the observations of currents, waves and wind. Waves were found to have a significant contribution to the trajectories, and we conclude that adding wave effects in ocean model systems is likely to increase predictability of surface drifter trajectories. The relative importance of the Stokes drift was twice as large as the direct wind drag for the used surface drifter.
相似文献16.
Observation-based evaluation of surface wave effects on currents and trajectory forecasts 总被引：4，自引：2，他引：2
Johannes R?hrs Kai H?kon Christensen Lars Robert Hole G?ran Brostr?m Magnus Drivdal Svein Sundby 《Ocean Dynamics》2012,62(10-12):1519-1533
Knowledge of upper ocean currents is needed for trajectory forecasts and is essential for search and rescue operations and oil spill mitigation. This paper addresses effects of surface waves on ocean currents and drifter trajectories using in situ observations. The data set includes colocated measurements of directional wave spectra from a wave rider buoy, ocean currents measured by acoustic Doppler current profilers (ADCPs), as well as data from two types of tracking buoys that sample the currents at two different depths. The ADCP measures the Eulerian current at one point, as modelled by an ocean general circulation model, while the tracking buoys are advected by the Lagrangian current that includes the wave-induced Stokes drift. Based on our observations, we assess the importance of two different wave effects: (a) forcing of the ocean current by wave-induced surface fluxes and the Coriolis–Stokes force, and (b) advection of surface drifters by wave motion, that is the Stokes drift. Recent theoretical developments provide a framework for including these wave effects in ocean model systems. The order of magnitude of the Stokes drift is the same as the Eulerian current judging from the available data. The wave-induced momentum and turbulent kinetic energy fluxes are estimated and shown to be significant. Similarly, the wave-induced Coriolis–Stokes force is significant over time scales related to the inertial period. Surface drifter trajectories were analysed and could be reproduced using the observations of currents, waves and wind. Waves were found to have a significant contribution to the trajectories, and we conclude that adding wave effects in ocean model systems is likely to increase predictability of surface drifter trajectories. The relative importance of the Stokes drift was twice as large as the direct wind drag for the used surface drifter. 相似文献
17.
Alexander Barth Aida Alvera-Azcárate Jean-Marie Beckers Joanna Staneva Emil V. Stanev Johannes Schulz-Stellenfleth 《Ocean Dynamics》2011,61(5):599-610
Surface winds are crucial for accurately modeling the surface circulation in the coastal ocean. In the present work, high-frequency
radar surface currents are assimilated using an ensemble scheme which aims to obtain improved surface winds taking into account
European Centre for Medium-Range Weather Forecasts winds as a first guess and surface current measurements. The objective
of this study is to show that wind forcing can be improved using an approach similar to parameter estimation in ensemble data
assimilation. Like variational assimilation schemes, the method provides an improved wind field based on surface current measurements.
However, the technique does not require an adjoint, and it is thus easier to implement. In addition, it does not rely on a
linearization of the model dynamics. The method is validated directly by comparing the analyzed wind speed to independent
in situ measurements and indirectly by assessing the impact of the corrected winds on model sea surface temperature (SST)
relative to satellite SST. 相似文献
18.
Simulation and detection of tsunami signatures in ocean surface currents measured by HF radar 总被引：3，自引：1，他引：2
Klaus-Werner Gurgel Anna Dzvonkovskaya Thomas Pohlmann Thomas Schlick Eric Gill 《Ocean Dynamics》2011,61(10):1495-1507
High-frequency (HF) surface wave radars provide the unique capability to continuously monitor the coastal environment far
beyond the range of conventional microwave radars. Bragg-resonant backscattering by ocean waves with half the electromagnetic
radar wavelength allows ocean surface currents to be measured at distances up to 200 km. When a tsunami propagates from the
deep ocean to shallow water, a specific ocean current signature is generated throughout the water column. Due to the long
range of an HF radar, it is possible to detect this current signature at the shelf edge. When the shelf edge is about 100 km
in front of the coastline, the radar can detect the tsunami about 45 min before it hits the coast, leaving enough time to
issue an early warning. As up to now no HF radar measurements of an approaching tsunami exist, a simulation study has been
done to fix parameters like the required spatial resolution or the maximum coherent integration time allowed. The simulation
involves several steps, starting with the Hamburg Shelf Ocean Model (HAMSOM) which is used to estimate the tsunami-induced
current velocity at 1 km spatial resolution and 1 s time step. This ocean current signal is then superimposed to modelled
and measured HF radar backscatter signals using a new modulation technique. After applying conventional HF radar signal processing
techniques, the surface current maps contain the rapidly changing tsunami-induced current features, which can be compared
to the HAMSOM data. The specific radial tsunami current signatures can clearly be observed in these maps, if appropriate spatial
and temporal resolution is used. Based on the entropy of the ocean current maps, a tsunami detection algorithm is described
which can be used to issue an automated tsunami warning message. 相似文献
19.
T. Ogawa 《Annales Geophysicae》1997,14(12):1454-1461
We briefly overview the radar observations that have been made for 30 years at Syowa Station, Antarctica for studying small-scale electron-density irregularities in the southern high-latitude E- and F-region ionosphere. Some observational results (i.e., long-term variations of radio aurora, Doppler spectra with narrow spectral widths and low Doppler velocities, and simultaneous observations of radar and optical auroras) from VHP radars capable of detecting 1.3- to 3-m scale irregularities are presented. A new 50-MHz radar system equipped with phased-antenna arrays began operation in February 1995 to observe two-dimensional behaviors of E-region irregularities. An HF radar experiment also began in February 1995 to explore decameter-scale E- and F-region irregularities in the auroral zone and polar cap. These two radars will contribute to a better understanding of the ionospheric irregularities and ionospheric physics at southern high latitudes. 相似文献
20.
Surface current mapping from HF/VHF coastal radars traditionally requires at least two distant sites. Vector velocities are
estimated by combining the radial velocity components measured by the radars. In many circumstances (e.g., failures, interferences,
logistics constraints), such a combination is not possible by lack of data from one station. Two methods are evaluated to
get information on surface circulation from a single site radar: the Vectorial Reconstruction Method (VRM) for current vector
mapping and the Vortex Identification Method (VIM) for detecting eddy-like structures. The VRM assumes a non-divergent horizontal
surface current, and the VIM analyzes radial velocities and their radial and orthoradial gradients. These two methods are
tested on modeled and measured data sets in the Northwestern Mediterranean Sea where both high-resolution ocean circulation
model and radar campaigns are available. The VRM performance is strongly limited by the divergence-free hypothesis which was
not satisfied in our real data. The VIM succeeded in detection of vortex in the Gulf of Lions and from an operating single
site radar located on the Provence coasts in summer. 相似文献