Microseismic events enhancement and detection in sensor arrays using autocorrelation‐based filtering          下载免费PDF全文

Entao Liu  Lijun Zhu  Anupama Govinda Raj  James H. McClellan  Abdullatif Al‐Shuhail  SanLinn I. Kaka  Naveed Iqbal 《Geophysical Prospecting》2017,65(6):1496-1509

Passive microseismic data are commonly buried in noise, which presents a significant challenge for signal detection and recovery. For recordings from a surface sensor array where each trace contains a time‐delayed arrival from the event, we propose an autocorrelation‐based stacking method that designs a denoising filter from all the traces, as well as a multi‐channel detection scheme. This approach circumvents the issue of time aligning the traces prior to stacking because every trace's autocorrelation is centred at zero in the lag domain. The effect of white noise is concentrated near zero lag; thus, the filter design requires a predictable adjustment of the zero‐lag value. Truncation of the autocorrelation is employed to smooth the impulse response of the denoising filter. In order to extend the applicability of the algorithm, we also propose a noise prewhitening scheme that addresses cases with coloured noise. The simplicity and robustness of this method are validated with synthetic and real seismic traces.  相似文献   

Simulating rainfall time-series: how to account for statistical variability at multiple scales?     

Fabio?OrianiEmail authorView author&#;s OrcID profile  Raj?Mehrotra  Grégoire?Mariethoz  Julien?Straubhaar  Ashish?Sharma  Philippe?Renard 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(2):321-340

Daily rainfall is a complex signal exhibiting alternation of dry and wet states, seasonal fluctuations and an irregular behavior at multiple scales that cannot be preserved by stationary stochastic simulation models. In this paper, we try to investigate some of the strategies devoted to preserve these features by comparing two recent algorithms for stochastic rainfall simulation: the first one is the modified Markov model, belonging to the family of Markov-chain based techniques, which introduces non-stationarity in the chain parameters to preserve the long-term behavior of rainfall. The second technique is direct sampling, based on multiple-point statistics, which aims at simulating a complex statistical structure by reproducing the same data patterns found in a training data set. The two techniques are compared by first simulating a synthetic daily rainfall time-series showing a highly irregular alternation of two regimes and then a real rainfall data set. This comparison allows analyzing the efficiency of different elements characterizing the two techniques, such as the application of a variable time dependence, the adaptive kernel smoothing or the use of low-frequency rainfall covariates. The results suggest, under different data availability scenarios, which of these elements are more appropriate to represent the rainfall amount probability distribution at different scales, the annual seasonality, the dry-wet temporal pattern, and the persistence of the rainfall events.  相似文献   

Upper layer circulation,hydrography, and biological response of the Andaman waters during winter monsoon based on in situ and satellite observations     

Salini Thaliyakkattil Chandran  Smitha Bal Raj  Sajeev Ravindran  Sanjeevan Vellorkirakathil Narayana 《Ocean Dynamics》2018,68(7):801-815

Upper layer circulation, hydrography, and biological response of Andaman waters during winter monsoon are assessed based on the observations carried out onboard FORV Sagar Sampada during January 2009 and November–December 2011. Cool and dry air carried by the moderate winds (6 m/s) from north and northeast indicates the influence of northeast monsoon (NEM) in the area during the observation time. The characteristics of physical parameters and the water mass indicate that the southeastern side is dominated by the less saline water from South China Sea intruded through the Malacca Strait, whereas the northeast is influenced by the freshwater from Ayeyarwady-Salween river system. The western side of the Andaman and Nicobar Islands exhibits similar properties of Bay of Bengal (BoB) water as evidenced in the T-S relation. Circulation pattern is uniform for the upper 88 m and is found to be more geostrophic rather than wind driven. Magnitude of the current velocity varies between 100 and 900 mm/s in November–December 2011 with strong current (900 mm/s) near Katchal and Nancowry islands and 100 and 1000 mm/s in January 2009 recording strong current (1000 mm/s) near the Little Nicobar Island. The Andaman waters are observed as less productive during the season based on the satellite-derived surface chl-a (0.1–0.4 mg/m³) and column-integrated primary productivity (PP) (100–275 mgC/m²/d).  相似文献   

Studies on Schumann Resonance Phenomena and Some Recent Advancements     

Abhijit Ghosh  Biswas  Debasish  Hazra  Pranab  Guha  Gautam  De  S. S. 《Geomagnetism and Aeronomy》2019,59(8):980-994

Geomagnetism and Aeronomy - Discrete spectra of frequencies at 8, 14, 20, 26, … Hz are generated by electromagnetic emission from lightning sources and can be regarded as excitation of AC...  相似文献   

Optimization of Biological Elimination of Ammonia and Chemical Oxygen Demand from Wastewater Using Response Surface Methodology          下载免费PDF全文

Sanak Ray  Ayusman Mohanty  Shakti S. Mohanty  Snehasish Mishra  Gautam Roy Chaudhury 《洁净——土壤、空气、水》2014,42(12):1744-1750

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Forecasting hourly particulate matter concentrations based on the advanced multivariate methods     

M. Perišić  D. Maletić  S. S. Stojić  S. Rajšić  A. Stojić 《International Journal of Environmental Science and Technology》2017,14(5):1047-1054

In this study, several multivariate methods were used for forecasting hourly PM₁₀ concentrations at four locations based on SO₂ and meteorological data from the previous period. According to the results, boosted decision trees and multi-layer perceptrons yielded the best predictions. The forecasting performances were similar for all examined locations, despite the additional PM₁₀ spatio-temporal analysis showed that the sites were affected by different emission sources, topographic and microclimatic conditions. The best prediction of PM₁₀ concentrations was obtained for industrial sites, probably due to the simplicity and regularity of dominant pollutant emissions on a daily basis. Conversely, somewhat weaker forecast accuracy was achieved at urban canyon avenue, which can be attributed to the specific urban morphology and most diverse emission sources. In conclusion to this, the integration of advanced multivariate methods in air quality forecasting systems could enhance accuracy and provide the basis for efficient decision-making in environmental regulatory management.  相似文献   

Extraction and analysis of geological lineaments of Kolli hills,Tamil Nadu: a study using remote sensing and GIS     

N. Jawahar Raj  A Prabhakaran  A Muthukrishnan 《Arabian Journal of Geosciences》2017,10(8):195

The aim of the present study is to investigate the lineaments of Kolli hills of Tamil Nadu State for which CARTOSAT-1 satellite’s DEM output has been made use of. The extracted lineaments were analysed using ArcGIS and Rockworks software. The total number and length of lineaments are 523 and 943.81 km, respectively. Shorter lineaments constitute about 3/4th of the total number of lineaments. The density of the lineaments varies from 0 to 7.41 km/km², and areas of very high to high density are restricted to the south central, central and north eastern parts, and these areas reflect the high degree of rock fracturing and shearing which makes these areas unsuitable for the construction of dams and reservoirs. However, these areas could be targeted for groundwater exploitation as they possess higher groundwater potential. The lineaments are oriented in diverse directions. However, those orienting in ENEWSW, NE-SW and NW-SE are predominating followed by those oriented in sub E-W and sub N-S directions. These orientations corroborate with results of previous regional studies and with orientations of prominent geological structures and features of the study area. Distinct variation in the predominant orientations of lineaments of varied sizes is observed, while the shorter ones are oriented in either NW-SE or NNW-SSE directions, the longer ones are oriented in either NE-SW or ENE-WSW. A comparative analysis of lineament datasets of the eight azimuth angles and the final lineament map underlines the need to extract lineaments from various azimuth angles to get a reliable picture about the lineaments.  相似文献   

A physical interpretation of the deterministic fractal–multifractal method as a realization of a generalized multiplicative cascade     

Andrea Cortis  Carlos E. Puente  Huai-Hsien Huang  Mahesh L. Maskey  Bellie Sivakumar  Nelson Obregón 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(6):1421-1429

In this study, we attempt to offer a solid physical basis for the deterministic fractal–multifractal (FM) approach in geophysics (Puente, Phys Let A 161:441–447, 1992; J Hydrol 187:65–80, 1996). We show how the geometric construction of derived measures, as Platonic projections of fractal interpolating functions transforming multinomial multifractal measures, naturally defines a non-trivial cascade process that may be interpreted as a particular realization of a random multiplicative cascade. In such a light, we argue that the FM approach is as “physical” as any other phenomenological approach based on Richardson’s eddies splitting, which indeed lead to well-accepted models of the intermittencies of nature, as it happens, for instance, when rainfall is interpreted as a quasi-passive tracer in a turbulent flow. Although neither a fractal interpolating function nor the specific multipliers of a random multiplicative cascade can be measured physically, we show how a fractal transformation “cuts through” plausible scenarios to produce a suitable realization that reflects specific arrangements of energies (masses) as seen in nature. This explains why the FM approach properly captures the spectrum of singularities and other statistical features of given data sets. As the FM approach faithfully encodes data sets with compression ratios typically exceeding 100:1, such a property further enhances its “physical simplicity.” We also provide a connection between the FM approach and advection–diffusion processes.  相似文献   

LRS Bianchi type?II disordered radiation model with a varying Λ term in self creation theory     

Mahesh Kumar Yadav  Vimal Chand Jain 《Astrophysics and Space Science》2011,331(1):343-349

In this paper, we study LRS Bianchi type II cosmological model with a nonzero time-dependent cosmological constant Λ for disordered radiation in the framework of Barber’s second self creation theory of gravitation. The physical and geometrical aspects of the model with singularities are also discussed.  相似文献   

Impact of Satellite Altimetry on Simulations of Sea Level Variability by an Indian Ocean Model     

S. K. Singh  Sujit Basu  Raj Kumar  Vijay K. Agarwal 《Marine Geodesy》2013,36(1):53-63

This article describes the impact of satellite altimeter data on the simulations of sea level variability (SLV) by a nonlinear reduced gravity model of the entire Indian Ocean. The model has been forced by 6-hourly analyzed wind stress data containing SSM/I observations and has been able to produce realistic circulation features. However, SLV values observed by Topex/Poseidon altimeter do not fit these simulations because of imperfect initial data. Hence an attempt has been made to initialize the model using altimeter data. The initialized model-generated SLVvalues have been compared with SLV derived by altimeter for monsoon as well as nonmonsoon months of 1996. Experimental runs have been performed for 10 days, 20 days, and one month. It has been found that the initialized model results on the final day of these experiments are in very good agreement with altimeter data of the same day. It is thus possible, in principle, to hindcast and forecast sea level variations in the time scale of 10 days to one month with the availability of good quality wind data for forcing the model and altimeter observations of sea level for initializing it.  相似文献