Inversion for the compressional wave speed profile of the bottomfrom synthetic aperture experiments conducted in the Hudson Canyon area     

Rajan  S.D. Doutt  J.A. Carey  W.M. 《Oceanic Engineering, IEEE Journal of》1998,23(3):174-187

In September 1988, a series of acoustic propagation experiments were conducted in the Hudson Canyon area. These included synthetic aperture experiments in which a source transmitting a set of four pure tones was towed toward/away from a vertical array of 24 receivers. Data obtained at 50 Hz during one of the synthetic aperture experiments are used to obtain a model for the compressional wave speed profile in the bottom using a modal inverse method. This model is further refined using 175 Hz data. The ability of the inferred model to predict the field at 50 Hz and higher frequencies is examined  相似文献   

Post-stack seismic inversion and attribute analysis in shallow offshore of Krishna-Godavari basin,India     

Baisakhi Das  Rima Chatterjee  Dip Kumar Singha  Rajan Kumar 《Journal of the Geological Society of India》2017,90(1):32-40

Seismic attributes such as: amplitude envelope, instantaneous phase and cosine of instantaneous phase of 2D post-stack seismic data facilitates structural and stratigraphic interpretation of shallow marine offshore, Krishna-Godavari basin. Two seismic sections namely, X and Y oriented N-S passing through wells W-1 andW-2 respectively are considered for seismic attribute analysis and porosity prediction. The gamma ray log trend indicates deposition of cleaning upward sediment. Coarsening upward, clayey-silty-sandy bodies, making a series of about 50-60 m thickness, have been evidenced from the gamma ray log. An extensional structural style comprising growth faults is associated with the progradational style of deposition. Four seismic zones have been distinguished. These zones differ in amplitude, frequency and continuity of the reflectors. Channel sands of Cretaceous age of Raghavapuram shale are identified in well log, seismic section and its acoustic impedance section. Major stratigraphic horizons along with faults extending to basement are marked with the help of attribute analysis. Porosity is mapped from transformation of acoustic impedance. The shales/unconsolidated sediments measure a high porosity with low impedance and the more porous sands are in an intermediate range. The predicted impedance and porosity values may be erroneous beyond the drilled depth because of non availability of well log data for calibration.  相似文献   

Effect of the variation in the lower tropospheric temperature on the wind onset of the Indian summer monsoon     

Kenji Taniguchi  Devraj Rajan  Toshio Koike 《Meteorology and Atmospheric Physics》2010,106(1-2):75-94

There is a large thermal contrast between the Arabian Peninsula and India (Δθ _AI) at the mature stage of the Indian summer monsoon (ISM). The forming process of Δθ _AI is investigated analyzing various datasets. It forms earlier in the lower troposphere than in the middle and upper layers. The potential temperature in the lower troposphere over the west coast of India (θ _IW) abruptly decreases in advance of the rapid enhancement of the westerly wind over the Arabian Sea corresponding to the ISM onset. Such a process was observed for all the target years and the rapid decrease in θ _IW could trigger the ISM onset. The decrease in θ _IW had two patterns. In one case, cooler air is brought by the strong winds around a cyclone over the Arabian Sea. In another case, θ _IW decreases gradually by a synergy of a southwesterly wind over the Arabian Sea and the enlargement of Δθ _AI.  相似文献   

Study of cloud liquid water path and total precipitable water from irs-p4/msmr and numerical weather prediction model output     

S.?Das  A.?S.?K.?A.?V.?Prasad?Rao  U.?C.?MohantyEmail author  A.?K.?Mitra  D.?Rajan 《Journal of the Indian Society of Remote Sensing》2004,32(2):175-184

A global weather analysis-forecast system is used to produce six hourly analysis of meteorological fields at roughly 150 km × 150 km resolution at the National Center for Medium Range Weather Forecast (NCMRWF). In this paper, we have studied the Total Precipitable Water Content (TPWC) and Cloud Liquid Water Path (CLWP) derived from the Indian Remote Sensing (IRS-P4) Satellite over the Indian Ocean region in relation to operational numerical weather prediction (NWP) model analysis and short-range forecasts. An objective analysis was carried out by introducing the observations of CLWP, TPWC and their values (six hour forecasts) from the T80 model as the first guess, for a 20 days period of August 1999 using the standard Cressman’s technique. The reanalysis could capture the signature of TPWC and CLWP data from IRS-P4 satellite. In general the observed values of TPWC and CLWP from IRS-P4 have a positive bias compared to NCMRWF analysis over the region where the satellite passed. The CLWP values have been compared with Special Sensor Microwave/Imager (SSM/I) products from the Defense Meteorological Satellite Program (DMSP) satellites. Results indicate that the model derived CLWP values were within acceptable limits, whereas the observations from the Multi-channel Scanning Microwave Radiometer (MSMR) showed slightly larger values.  相似文献   

Exploration and Research for Atomic Minerals     

K.D.P. Singh  D. Narasimhan  P. Rajasekaran  Rajan B. Jain 《Gondwana Research》2005,8(4):637

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Chondrule-like objects and brown glasses in howardites     

Edward J. Olsen  Kurt Fredriksson  Sundar Rajan  Albert Noonan 《Meteoritics & planetary science》1990,25(3):187-194

Abstract— Chondrule-like objects and brown glasses were analyzed in the howardites, Bununu, Malvern, Monticello, Pavlovka, and Yamato 7308. The objects are very similar to chondrules in ordinary and carbonaceous chondrites. Like the brown glasses the chondrule-like objects could have been produced by impact melting that left some crystalline nuclei, followed by a slower cooling rate than for the glasses. Alternatively, these objects are chondrules implanted from chondrite impactors. They are, however, without rims or any adhering matrix. The brown glasses appear to represent melting of average regolithic surface material, except for Monticello and Y7308, both of which have some siliceous glasses. The siliceous glasses could not have been produced by vapor fractionation but by melting of differentiated lithologies such as fayalitic granites. Impact mechanics indicates that howardites with abundant brown glasses came from an asteroid larger than Vesta (>400 km radius), upon which impacts occurred at relative velocities of up to 5 km/s. Howardites with little or no brown glasses came from a smaller parent body. We conclude that at least two parent bodies are likely sources for the basaltic achondrites.  相似文献   

Neon and argon in the Allende meteorite     

S.P Smith  J.C Huneke  R.S Rajan  G.J Wasserburg 《Geochimica et cosmochimica acta》1977,41(5):627-647

Trapped and cosmogenic Ne and Ar were measured in Ca,Al-rich aggregates and chondrules, mafic chondrules, and bulk and matrix samples from the Allende C3V chondritic meteorite to investigate the possible occurrence of anomalous isotopic compositions of noble gases that would correlate with oxygen or magnesium isotopic anomalies previously found in this meteorite.Large enrichments of both ²²Ne and ³⁶Ar were observed in low-temperature release fractions from several Ca,Al-rich inclusions, but the enrichments are consistent with galactic cosmic-ray production of ²²Ne by spallation from sodium and ³⁶Ar by neutron capture on chlorine. Trapped neon in matrix samples is comprised of two distinctive compositions, with (²⁰Ne/²²Ne)_t equal to 8.7 ± 0.1 and 10.4 ± 1.0, that appear to correlate with the two gas-rich trace phases chromite/carbon and ‘Q’ described by Lewis et al. (1975). Several Ca,Al-rich aggregates which have high contents of the volatile elements Na, Cl, K, and Rb also contain trapped neon. However, no neon-E has been identified in any of the samples studied, including samples of several inclusions known to contain isotopically anomalous oxygen and magnesium.  相似文献   

Chondrules in the Qingzhen type-3 enstatite chondrite: Possible precursor components and comparison to ordinary chondrite chondrules     

Jeffrey N. Grossman  Alan E. Rubin  Ermanno R. Rambaldi  R.Sundar Rajan  John T. Wasson 《Geochimica et cosmochimica acta》1985,49(8):1781-1795

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The Legal Continental Shelf: Geosciences at sea with UNCLOS     

S. Rajan 《Journal of the Geological Society of India》2018,92(2):131-133

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Weathering Controlled Landslide in Deccan Traps: Insight from Mahabaleshwar,Maharashtra     

Mayank Joshi  S. Rajappan  P. Prasobh Rajan  J. Mathai  G. Sankar  V. Nandakumar  V. Anil Kumar 《Journal of the Geological Society of India》2018,92(5):555-561

Landslide is one of the devastating natural phenomenon that threatens human life and property. Every year a number of persons lost their lives due to the landslides. Therefore, a better understanding and characterization of landslide is very essential for adopting mitigation strategies to contain the adversities of this natural hazard. Information on landslides from different climatic setup are very essential for better understanding of the influence of weathering, rainfall, or topography on landslide generation. Weathering is one of the important causative factor for landslide generation in the moderate topography or inactive mountainous terrain. The Western Ghats including the Deccan Traps, an inactive mountain range, receives torrential rainfall. Intense rainfall in these areas enhances the weathering processes and fabricates thick soil covers. Mahabaleshwar area, Maharashtra was chosen as a case study, where high elevated part is covered by lateritic layer and each lava flow unit is separated by a thin weathered bed of red bole. The area experiences series of landslides during the summer monsoon months. Mainly two types of landslides have been identified in the area confined with the red bole bed and powdery lateritic soil. The first type of landslides occur at higher elevations (≥1200m) where horizontal beds of permeable laterites underlined by impermeable thick basalt beds. The rain water infiltrates down and spread laterally within the permeable lateritic beds. It finally spouts at lower plateau elevations and triggers mainly debris flows. The other category of landslides occurs where the weathered red bole bed separates two successive lava flows. The percolating water from the secondary porosities (joints and inter connected vugs) comes out from the contact zones of basalt and red bole bed in the form of seepages. It erodes the red bole bed and as a result the overlying masses hang and consequently lead to rock fall. The Chemical Index of Alteration (CIA) of the representative samples from landslide locations indicates significant weathering. The CIA values for the fine lateritic soil are up to 98% whereas for the red bole bed it varies from 77 to 85%. This suggests a high chemical weathering and higher erodibility. The association of active landslide locations with the red bole bed and fine lateritic soil suggests a close relation between weathering and landslide occurrences in the area.  相似文献