Estimation of water cloud model vegetation parameters using a genetic algorithm     

Kamal Kumar  K.S. Hari Prasad  M.K. Arora 《水文科学杂志》2013,58(4):776-789

Abstract

The water cloud model is used to account for the effect of vegetation water content on radar backscatter data. The model generally comprises two parameters that characterize the vegetated terrain, A and B, and two bare soil parameters, C and D. In the present study, parameters A and B were estimated using a genetic algorithm (GA) optimization technique and compared with estimates obtained by the sequential unconstrained minimization technique (SUMT) from measured backscatter data. The parameter estimation was formulated as a least squares optimization problem by minimizing the deviations between the backscatter coefficients retrieved from the ENVISAT ASAR image and those predicted by the water cloud model. The bias induced by three different objective functions was statistically analysed by generating synthetic backscatter data. It was observed that, when the backscatter coefficient data contain no errors, the objective functions do not induce any bias in the parameter estimation and the true parameters are uniquely identified. However, in the presence of noise, these objective functions induce bias in the parameter estimates. For the cases considered, the objective function based on the sum of squares of normalized deviations with respect to the computed backscatter coefficient resulted in the best possible estimates. A comparison of the GA technique with the SUMT was undertaken in estimating the water cloud model parameters. For the case considered, the GA technique performed better than the SUMT in parameter estimation, where the root mean squared error obtained from the GA was about half of that obtained by the SUMT.

Editor D. Koutsoyiannis; Associate editor L. See

Citation Kumar, K., Hari Prasad, K.S. and Arora, M.K., 2012. Estimation of water cloud model vegetation parameters using a genetic algorithm. Hydrological Sciences Journal, 57 (4), 776–789.  相似文献   

Analysis of unusual meteorological conditions that led to recent floods in Bhagirathi basin (Uttarakhand Himalayas)     

Manohar Arora  Rakesh Kumar  R.D. Singh  Jatin Malhotra  Naresh Kumar 《水文科学杂志》2013,58(7):1238-1243

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Radon-thoron monitoring in Tatun volcanic areas of northern Taiwan using LR-115 alpha track detector technique: Pre-calibration and installation   总被引：1，自引：0，他引：1  

Arvind Kumar  Vivek Walia  Tsanyao Frank Yang  Hsiao-Hsien Chang  Shih-Jung Lin  Karumpil Philips Eappen  Baldev Raj Arora 《Acta Geophysica》2013,61(4):958-976

In the present study, experiments have been carried out to calibrate LR-115 alpha detector films in bare and cup-mode exposure for the measurement of radon and thoron concentrations in soil gas. Results showed non-uniformity in track formation on the films in bare-mode exposure. However, in cup-mode exposure the non-uniformity was reduced to a greater extent. The calibration factors obtained for radon in bare- and cup-mode exposures are 0.049 and 0.034 tr. cm^?2 per Bq m^?3 d, respectively. An attempt has been made to calibrate the radon-thoron discriminative cup with LR-115 films for simultaneous measurements of radon and thoron. This paper also presents the preliminary results of radonthoron monitoring in Tatun volcanic areas of northern Taiwan for the first time using radon-thoron discriminators with LR-115 films. The results show that the safe temperature to install the LR-115 films in volcanic areas is ≤ 65°C and thoron concentration in the study area is low.  相似文献   

Space-time seismicity and earthquake swarms: Certain observations along the slow-spreading mid-Indian Ocean ridges     

M. Radha Krishna  S. K. Arora 《Journal of Earth System Science》1998,107(2):161-173

The slow spreading mid-Indian Ocean ridge system containing the Carlsberg, Central and Southwest Indian ridges is seismically very active. In the present study, a detailed analysis has been carried out of the data of earthquake sources along different ridge segments in order to investigate the spatial and temporal clustering patterns and to evaluate crustal processes related to the swarm occurrences along these ridges. The spatial and temporal clustering pattern of the recent earthquakes (1980–1990) pertaining to nine major spreading segments and eight fracture zones suggests that the events cluster in greater proportion along the spreading segments than along the fracture zones. We performed a systematic search of earthquake catalogue during the period 1964–1990 by examining the spatio-temporal hypocentral clusters in order to identify the swarm occurrences along these ridges. The search included eighteen prominent sequences, of which, thirteen were earthquake swarms. Except two, all other swarms were found to be occurring mainly on the spreading segments. The maximum magnitude observed in these swarms is m_b = 5.4 and have many events predominantly showing normal faulting mechanisms. The spatial disposition and temporal activity of the events in swarms is much similar to the foreshock-mainshock-aftershock sequences observed along the spreading rift valley zones. These characteristics help us to support that swarms along the slow spreading mid-Indian Ocean ridges are the result of extensional tectonic activity, leading to the development of the median valley topography, a mechanism similar to that proposed by Bergman and Solomon (1990) for the Mid-Atlantic Ridge.  相似文献   

Hydromagnetic flow between two parallel planes,one oscillating and the other fixed     

P. R. Gupta  K. L. Arora 《Pure and Applied Geophysics》1974,112(2):498-505

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A magnetometer array study in northwest India     

F.E.M. Lilley  B.P. Singh  B.R. Arora  B.J. Srivastava  S.N. Prasad  M.N. Sloane 《Physics of the Earth and Planetary Interiors》1981,25(3):232-240

A magnetometer array study has been carried out in northwest India, from Rajasthan across the Indo-Gangetic Plain into the Himalayan foothills. Over the three months of operation, a wide variety of natural geomagnetic events has been recorded. The analysis of a simple substorm, polarized just west of north, shows a strong anomaly in the form of a reversal of the vertical component of the fluctuation, both in the Himalayan foothills and on the Ganga Plain.The magnetic fluctuations pattern observed is most directly interpreted in terms of a path of concentrated current flow in the Earth, striking across the Himalaya. It is evidently aligned with the Aravalli belt which outcrops further south, and may indicate that some geological structure in the sub-basement is of abnormally high electrical conductivity. The path of such a current concentration across the foothills raises the question whether some transverse structure in the Himalaya is not acting as a bridge to Peninsular India for current induced in the Tibetan plateau to the northeast.  相似文献   

Signal-to-noise-ratio improvement of a linear seismic array     

J. R. Arora 《Pure and Applied Geophysics》1968,69(1):25-45

Summary The aim of this paper is improvement in signal-to-noise-ratio (SNR) through the use of a linear seismic array. The noise is considered to be composed of a coherent part with nature similar to that of incoming signals and an incoherent part having a constant power all across the array. All possible values of seismometer positions which minimise the coherent noise power are derived. Advantages of the delayed-summation processing technique, in so far as it enables us to obtain superior values of the signal-to-noise-ratio improvement, and furnishes unique values of signal wavelengths and signal amplitudes as compared to the simple-summation technique which gives relatively inferior values ofSNR, and enables us to obtain the signal wave-lengths as solutions of a trigonometric equation are brought out analytically. Being suitable for field work due to its simple nature, the simplesummation technique is studied in detail. Upper limit on the value of array aperture for actual improvement of all the expected signals are found. Requirements to be met for achieving the optimum value of theSNR improvement are deduced.  相似文献   

Choice of a teleseismicP-wave travel-time model and the associated source corrections     

S. K. Arora  C. A. Krishnan 《Pure and Applied Geophysics》1972,101(1):74-89

Summary Among various trial models ofP-wave travel times, there exists at least one model which best predicts the times of first arrivals from a certain region at a set of recording stations even if no attempt is made to correct the travel-time standards against known station errors and source bias. In teleseismic distance range (25°100°) and surface-focus case, the possibility of statistically establishing which of the twoP models, viz. Jeffreys-Bullen and Herrin, is more appropriate for each of the four source regions, viz. Southern Nevada, Aleutian Islands, Eastern Kazakh and Novaya Zemlya, is discussed in this paper. Data corresponding to a set of underground explosions from these regions form the basis of such an analysis. The Herrin model is found to be better applied to Aleutian Islands region while the Jeffreys-Bullen model seems more appropriate for each of the remaining three regions.As a result of the study of the travel-time models, numerical estimates of space and time corrections pertaining to the above mentioned regions, based on the most appropriate model and directly applicable to the computed source parameters, are obtained. On applying these corrections, the size of source location error ellipse and the source-time error reduce to very small representative values, viz. 4 km×6 km (area 75 km²) and ±0.2 sec respectively.  相似文献   

Study of water cloud model vegetation descriptors in estimating soil moisture in Solani catchment   总被引：2，自引：0，他引：2       下载免费PDF全文

Kamal Kumar  Hari Prasad Suryanarayana Rao  M. K. Arora 《水文研究》2015,29(9):2137-2148

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Separation of diffracted waves in transversely isotropic media     

Yogesh Arora  Ilya Tsvankin 《Studia Geophysica et Geodaetica》2016,60(3):487-499

Imaging diffracted waves can provide useful information about complex subsurface geology and fracture networks. Separation of diffractions from typically more intensive reflected events can be done based on specularity, which measures deviation from Snell’s law. Here, we analyze two formulations of specularity and their applicability to diffraction processing in the presence of anisotropy. We show that the most common definition of specularity, originally introduced for pure modes in isotropic media, remains valid for both pure and converted waves in arbitrarily anisotropic models. The other formulation operates directly with the difference between the slowness projections onto the reflector for the incident and reflected waves. Testing on a VTI (transversely isotropic with a vertical symmetry axis) diffraction ramp model demonstrates that both formulations produce satisfactory results for anisotropic media with appropriate tapering of the specularity gathers. Then separation and imaging of diffractions is performed for the structurally complex VTI Marmousi model. We also analyze the sensitivity of diffractions in the specularity gathers to errors in the symmetry-direction velocity and anellipticity parameter η.  相似文献