Spectral Combination of Spherical Gradiometric Boundary-Value Problems: A Theoretical Study     

Mehdi Eshagh 《Pure and Applied Geophysics》2012,169(12):2201-2215

The Earth’s gravity potential can be determined from its second-order partial derivatives using the spherical gradiometric boundary-value problems which have three integral solutions. The problem of merging these solutions by spectral combination is the main subject of this paper. Integral estimators of biased- and unbiased-types are presented for recovering the disturbing gravity potential from gravity gradients. It is shown that only kernels of the biased-type integral estimators are suitable for simultaneous downward continuation and combination of gravity gradients. Numerical results show insignificant practical difference between the biased and unbiased estimators at sea level and the contribution of far-zone gravity gradients remains significant for integration. These contributions depend on the noise level of the gravity gradients at higher levels than sea. In the cases of combining the gravity gradients, contaminated with Gaussian noise, at sea and 250?km levels the errors of the estimated geoid heights are about 10 and 3 times smaller than those obtained by each integral.  相似文献   

The PBRM (perception-based regional mapping): A spatial method to support regional development initiatives     

Mehdi Saqalli  Patrick Caron  Pierre Defourny  Ali Issaka 《Applied geography (Sevenoaks, England)》2009,29(3):358-370

This paper examines the relevance of a perception-based regional level mapping tool in rural Niger. Two regions in Niger are examined. Results permit to assume that such a tool helped to fill several gaps: (i) a scale gap between local and nation wide studies; (ii) a scientific gap between biophysical and socio-anthropological sciences; and (iii) a methodological gap of integration between data sources. Moreover, this method is fast, cheap and action-oriented. Data are easily understandable and usable both by rural communities and development agencies. It provides information about human dynamics at a regional level, which cannot be achieved by other methods.  相似文献   

A geoid solution for airborne gravity data   总被引：2，自引：0，他引：2  

Lars E. Sjöberg  Mehdi Eshagh 《Studia Geophysica et Geodaetica》2009,53(3):359-374

Airborne gravity data is usually attached with satellite positioning of data points, which allow for the direct determination of the gravity disturbance at flight level. Assuming a suitable gridding of such data, Hotine’s modified integral formula can be combined with an Earth Gravity Model for the computation of the disturbing potential (T) at flight level. Based on T and the gravity disturbance data, we directly downward continue T to the geoid, and we present the final solution for the geoid height, including topographic corrections. It can be proved that the Taylor expansion of T converges if the flight level is at least twice the height of the topography, and the terrain potential will not contribute to the topographic correction. Hence, the simple topographic bias of the Bouguer shell yields the only topographic correction. Some numerical results demonstrate the technique used for downward continuation and topographic correction.  相似文献   

Wavelet and Gaussian Approaches for Estimation of Groundwater Variations Using GRACE Data          下载免费PDF全文

Farzam Fatolazadeh  Behzad Voosoghi  Mehdi Raoofian Naeeni 《Ground water》2016,54(1):74-81

In this study, a scheme is presented to estimate groundwater storage variations in Iran. The variations are estimated using 11 years of Gravity Recovery and Climate Experiments (GRACE) observations from period of 2003 to April 2014 in combination with the outputs of Global Land Data Assimilation Systems (GLDAS) model including soil moisture, snow water equivalent, and total canopy water storage. To do so, the sums of GLDAS outputs are subtracted from terrestrial water storage variations determined by GRACE observations. Because of stripping errors in the GRACE data, two methodologies based on wavelet analysis and Gaussian filtering are applied to refine the GRACE data. It is shown that the wavelet approach could better localize the desired signal and increase the signal‐to‐noise ratio and thus results in more accurate estimation of groundwater storage variations. To validate the results of our procedure in estimation of ground water storage variations, they are compared with the measurements of pisometric wells data near the Urmia Lake which shows favorable agreements with our results.  相似文献   

Fracture characterization using converted waves          下载免费PDF全文

Mehdi E. Far  Bob Hardage 《Geophysical Prospecting》2016,64(2):287-298

We present a method for inversion of fracture compliance matrix components from wide‐azimuth noisy synthetic PS reflection data and quantitatively show that reflection amplitude variations with offset and azimuth for converted PS‐waves are more informative than P‐waves for fracture characterization. We consider monoclinic symmetry for fractured reservoir (parameters chosen from Woodford Shale), which can be formed by two or more sets of vertical fractures embedded in a vertically transverse isotropic background. Components of effective fracture compliance matrices for a medium with monoclinic symmetry are related to the characteristics of the fractured medium. Monte Carlo simulation results show that inversion of PS reflection data is more robust than that of PP reflection data to uncertainties in our a priori knowledge (vertically transverse isotropic parameters of unfractured rock) than PP reflection data. We also show that, while inversion of PP reflections is sensitive to contrasts in elastic properties of upper and lower media, inversion of PS reflections is robust with respect to such contrasts.  相似文献   

The dichotomous Markov process with nonparametric test application; a decision support method in long-term river behavioural analysis: the Zayandeh Rud River; a case study from central Iran   总被引：1，自引：1，他引：0  

Mehdi F. Harandi  Shantia Yarahmadian  Mohammad Sepehrifar  Pieter H. A. J. M. van Gelder 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(7):1889-1896

We use the Dichotomous Markov Noise model with constant transition rates to describe the dynamics of fluctuations in the water level as a stochastic process, which is imposed on river discharge changes. By applying this model, two different regimes are determined for the long-term behaviour of the river. Based on these regimes, we define two nonparametric classes of the overall increasing/decreasing nature of the water level in the long-term behaviour, which are separated by an exponential steady state regime. In this paper, we develop a nonparametric testing procedure to test exponentially (steady state regime) against an alternative overall decreasing level distribution. The proposed test predicts the long-term regime behaviour of the river. The mathematical tools introduced to handle the problem should be of general use and the testing procedure can be considered as a new mathematical tool in the study of water level dynamics. Under conditions of data austerity and as a case of study, we examine the stochastic characteristics of the Zayandeh Rud (Zāyandé-Rūd or Zāyanderūd, also spelled as Zayandeh-Rood or Zayanderood) River (Isfahan, Iran) water level.  相似文献   

Ground motion record simulation for structural analysis by consideration of spectral acceleration autocorrelation pattern   总被引：1，自引：1，他引：0  

Alireza Azarbakht  Mahdi Sadeghi  Mehdi Mousavi 《地震工程与工程振动(英文版)》2014,13(2):195-202

A novel approach is introduced to generate simulated ground motion records by considering spectral acceleration correlations at multiple periods. Most of the current reliable Ground Motion Record(GMR) simulation procedures use a seismological model including source, path and site characteristics. However, the response spectrum of simulated GMR is somewhat different when compared with the response spectrum based on recorded GMRs. More specifi cally, the correlation between the spectral values at multiple periods is a characteristic of a record which is usually different between simulated and recorded GMRs. As this correlation has a signifi cant infl uence on the structural response, it is needed to investigate the consistency of the simulated ground motions with actual records. This issue has been investigated in this study by incorporating an optimization algorithm within the Boore simulation technique. Eight seismological key parameters were optimized in order to achieve approximately the same correlation coeffi cients and spectral acceleration between two sets of real and simulated records. The results show that the acceleration response spectra of the synthetic ground motions also have good agreement with the real recorded response spectra by implementation of the proposed optimized values.  相似文献   

Adaptive state estimation of groundwater contaminant boundary input flux in a 2-dimensional aquifer     

Muhammad Malik Nauman  Murtuza Mehdi  Asif Iqbal  Muhammad Saifullah Abu Bakar  Brahim Aissa  Dk Nur Afiqah Jalwati Puteri  Amer Farhan Rafique 《地下水科学与工程》2019,(4):373-382

In many circumstances involving heat and mass transfer issues,it is considered impractical to measure the input flux and the resulting state distribution in the domain.Therefore,the need to develop techniques to provide solutions for such problems and estimate the inverse mass flux becomes imperative.Adaptive state estimator(ASE)is increasingly becoming a popular inverse estimation technique which resolves inverse problems by incorporating the semi-Markovian concept into a Bayesian estimation technique,thereby developing an inverse input and state estimator consisting of a bank of parallel adaptively weighted Kalman filters.The ASE is particularly designed for a system that encompasses independent unknowns and/or random switching of input and measurement biases.The present study describes the scheme to estimate the groundwater input contaminant flux and its transient distribution in a conjectural two-dimensional aquifer by means of ASE,which in particular is because of its unique ability to efficiently handle the process noise giving an estimation of keeping the relative error range within 10%in 2-dimensional problems.Numerical simulation results show that the proposed estimator presents decent estimation performance for both smoothly and abruptly varying input flux scenarios.Results also show that ASE enjoys a better estimation performance than its competitor,Recursive Least Square Estimator(RLSE)due to its larger error tolerance in greater process noise regimes.ASE's inherent deficiency of being slower than the RLSE,resulting from the complexity of algorithm,was also noticed.The chosen input scenarios are tested to calculate the effect of input area and both estimators show improved results with an increase in input flux area especially as sensors are moved closer to the assumed input location.  相似文献   

Critical plane analysis for interpreting experimental results on anisotropic rocks     

Pouragha  Mehdi  Wan  Richard  Eghbalian  Mahdad 《Acta Geotechnica》2019,14(4):1215-1225

  相似文献   

Quantification of source-to-site distance uncertainty in ground motion models     

Yaghmaei-Sabegh  Saman  Ebrahimi-Aghabagher  Mehdi 《Natural Hazards》2019,99(1):287-306

Natural Hazards - Among different input data, source-to-site distance plays a major role in the results of ground motion models (GMMs). In order to determine the source-to-site distance, geometric...  相似文献