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641.
Suchandra Aich Bhowmick Rashmi Sharma K. N. Babu A. K. Shukla Raj Kumar R. Venkatesan 《Marine Geodesy》2015,38(3):193-205
The focus of this study is the validation of significant wave height (SWH) and sea surface height anomaly (SSHA) obtained from the first Ka-band altimeter AltiKa onboard SARAL (Satellite for ARGOS and Altimeters). It is a collaborative mission of the Indian Space Research Organization and Centre National d'Etudes Spatiales (CNES). This is done using in-situ observations from buoy and Jason-2 measurements. Validation using buoy observations are at particular locations while that using Jason-2 altimeter is an attempt towards global validation of Altika products. The results clearly indicate that the SARAL/AltiKa provide high-quality data and the errors are within a predefined range of accuracy. A parallel validation of SWH from other altimeters, which monitored ocean since last decade, like EnviSAT and Jason-2 was also performed with buoy observations. The results clearly show that the accuracy of AltiKa SWH is much better than EnviSAT and comparable to reference mission Jason-2. The accuracy is quite good for the calm sea while in the rough seas the accuracy degrades some. The inter-comparison of SARAL/AltiKa SSHA with Jason-2 indicates a fair match between them. These validation exercises demonstrate the high quality of AltiKa products, usable for practical applications. 相似文献
642.
N. Satyavani Kalachand Sain Malcolm Lall B. J. P. Kumar 《Marine Geophysical Researches》2008,29(3):167-175
Seismic data from the Andaman offshore region has been examined to investigate for the presence of gas hydrates. The seismic
data displays reflection characteristics such as blanking, enhanced reflection patterns, shadows in instantaneous frequency,
and increase in amplitude with the offset, which are indicative of gas hydrates and underlying free gas. A prominent bottom-simulating
reflection, BSR, coupled with reverse polarity is observed around 650–700 ms. Seismic attributes such as the reflection strength
and instantaneous frequency are computed along this reflector in order to probe for the presence of gas hydrates or free gas
in this region. The reflection plot shows a strong reflector paralleling the seafloor. In addition, attenuation of the high
frequency signal is noticed, indicating the presence of free gas below the BSR. 相似文献
643.
Anil Kumar Vijayan Takashi Yoshikawa Shigeki Watanabe Hiroaki Sasaki Kazuhiko Matsumoto Sei-Ichi Saito Shigenobu Takeda Ken Furuya 《Journal of Oceanography》2009,65(2):245-258
Regional variations in the contribution of non-photosynthetic pigments (ā
np*) to the total light absorption of phytoplankton (ā
ph*) and its influence on the maximum quantum yield of photosynthesis (φ
m) were investigated. In the western equatorial Pacific, the surface ā
np* : ā
ph* ratio was higher in the western warm pool than that in the upwelling region. This difference appears to be attributable to
severe nitrate depletion and higher percentage of prokaryotes, which can accumulate very high concentrations of zeaxanthin
in the western warm pool. In the subarctic North Pacific, the ā
np* : ā
ph* ratio was expected to be higher in the Alaskan Gyre where the thermocline is sharper and iron limitation may possibly be
more severe than in the Western Subarctic Gyre. However, the ratio was actually higher in the Western Subarctic Gyre, contradictory
to our expectations. This east-west variation appears to be attributable to changes in the taxonomic composition; cyanobacteria
were more abundant in the Western Subarctic Gyre. The values of ā
np* : ā
ph* and its vertical variations were relatively small in the subarctic North Pacific compared to those in the western equatorial
Pacific. These inter-regional variations appear to be attributable to the lower solar radiation intensity, smaller percentage
of cyanobacteria, and relatively strong vertical mixing in the subarctic North Pacific. The spatial variations in ā
np* : ā
ph* significantly influence φ
m. In comparison with φ
m based on the total light absorption (φ
m ph), the values corrected for the contribution of non-photosynthetic pigments (φ
m ps) showed an increase in both the western equatorial Pacific and the subarctic North Pacific. 相似文献
644.
The significant wave height and wind speed derived for the period 1993–2010 from altimeter data sets over the Arabian Sea, Bay of Bengal, and the Indian Ocean categorized as six zones has been analyzed. The average variation of both significant wave height and wind speed is found to be almost stable for the period of study. The study reveals that the average wind speed increases by about 6cm/sec/year during monsoon and post monsoon in the southern Indian Ocean. The distribution of wind and waves was studied in the context of seasonal variations. In addition, the average inter-annual and intra-annual variations along with the statistical parameters such as standard deviation, and root mean square wave height for the six zones are also reported in this paper. 相似文献
645.
646.
Acta Geotechnica - Experimental studies indicate that the yield parameters for soils remain generally stress dependent, in which case, the internal friction angle reduces continuously with an... 相似文献
647.
Pramod Kumar Yadav P K Adhikari Shalivahan Srivastava Ved P Maurya Anurag Tripathi Shailendra Singh Roshan K Singh Ashish K Bage 《Journal of Earth System Science》2018,127(2):17
Dalma volcanics (DVs) has intruded the older Singhbhum Group of Metapelites. Despite DVs being rich in mineralisation, its boundaries are not clearly demarcated. Gravity and magnetic surveys have been attempted for mapping the boundaries in DVs. These surveys were made in the northern fringe of the DVs over an area of \(\sim \)0.70 \(\hbox {km}^{2}\) along 13 parallel lines at 50 m spacing. The data was acquired at \(\sim \)25 \(\hbox {m}\) spacing. The surveys were taken for determination of lithological boundaries, depths and nature of causative source using Euler depth solutions and radially averaged power spectrum (RAPS). Residual anomaly maps of gravity and magnetic intensity show the same trend as that of Bouguer gravity anomaly and total magnetic intensity anomaly map indicating towards shallow sources. The magnetic map in general follows the same pattern as that of gravity anomaly maps. The map shows coincident high gravity and magnetic anomalies. These anomalies together with resistivity signatures confirm that the northern fringe of DVs hosts volcanogenic massive sulphide settings. The Euler depth solution delineated the lateral boundaries and nature of the source. It seems that the source is of spherical nature lying within a depth range of 25–40 m. The obtained lithological (vertical) units from RAPS are between Lower DVs, Upper DVs and Singhbhum Group Metapelites at depths of \(\sim \)15, \(~\sim \)25 and \(\sim \)40 \(\hbox {m}\), respectively. The metallogeny is associated with the Upper DVs and the corresponding delineated lithological (vertical) unit is indicative of the top of the ore body. Good agreement is observed with the geological succession from the drilling data and resistivity data. The findings suggest that the northern fringe of DVs could be a preferred target for drilling. 相似文献
648.
Forecasting of hydrologic time series, with the quantification of uncertainty, is an important tool for adaptive water resources management. Nonstationarity, caused by climate forcing and other factors, such as change in physical properties of catchment (urbanization, vegetation change, etc.), makes the forecasting task too difficult to model by traditional Box–Jenkins approaches. In this paper, the potential of the Bayesian dynamic modelling approach is investigated through an application to forecast a nonstationary hydroclimatic time series using relevant climate index information. The target is the time series of the volume of Devil's Lake, located in North Dakota, USA, for which it was proved difficult to forecast and quantify the associated uncertainty by traditional methods. Two different Bayesian dynamic modelling approaches are discussed, namely, a constant model and a dynamic regression model (DRM). The constant model uses the information of past observed values of the same time series, whereas the DRM utilizes the information from a causal time series as an exogenous input. Noting that the North Atlantic Oscillation (NAO) index appears to co‐vary with the time series of Devil's Lake annual volume, its use as an exogenous predictor is explored in the case study. The results of both the Bayesian dynamic models are compared with those from the traditional Box–Jenkins time series modelling approach. Although, in this particular case study, it is observed that the DRM performs marginally better than traditional models, the major strength of Bayesian dynamic models lies in the quantification of prediction uncertainty, which is of great value in hydrology, particularly under the recent climate change scenario. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
649.
The ultimate bearing capacity of a group of equally spaced multiple rough strip footings was determined due to the contribution of soil unit weight. The analysis was performed by using an upper bound theorem of limit analysis in combination with finite elements and linear programming. Along the interfaces of all the triangular elements, velocity discontinuities were considered. The value of ξγ was found to increase continuously with a decrease in S/B, where (i) ξγ is the ratio of the failure load of an interfering strip footing of a given width (B) to that of a single isolated strip footing having the same width and (ii) S is the clear spacing between any two adjacent footings. The effect of the variation of spacing on ξγ was found to be very extensive for small values of S/B; ξγ approaches infinity at S/B=0. In all the cases, the velocity discontinuities were found to exist generally in a zone only around the footing edge. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
650.
Ocean Dynamics - Fourth-order nonlinear evolution equation (NLEE), which is an excellent starting point for the analysis of nonlinear deep water surface waves, are used here to investigate the... 相似文献