Retrieval of sea surface velocities using sequential Ocean Colour Monitor (OCM) data

The Indian remote sensing satellite, IRS-P4 (Oceansat-I) launched on May 26th, 1999 carried two sensors on board, i.e., the Ocean Colour Monitor (OCM) and the Multi-frequency Scanning Microwave Radiometer (MSMR) dedicated for oceanographic research. Sequential data of IRS-P4 OCM has been analysed over parts of both east and west coast of India and a methodology to retrieve sea surface current velocities has been applied. The method is based on matching suspended sediment dispersion patterns, in sequential two time lapsed images. The pattern matching is performed on a pair of atmospherically corrected and geo-referenced sequential images by Maximum Cross-Correlation (MCC) technique. The MCC technique involves computing matrices of cross-correlation coefficients and identifying correlation peaks. The movement of the pattern can be calculated knowing the displacement of windows required to match patterns in successive images. The technique provides actual flow during a specified period by integrating both tidal and wind influences. The current velocities retrieved were compared with synchronous data collected along the east coast during the GSI cruise ST-133 of R.V. Samudra Kaustubh in January 2000. The current data were measured using the ocean current meter supplied by the Environmental Measurement and CONtrol (EMCON), Kochi available with the Geological Survey of India, Marine Wing. This current meter can measure direction and magnitude with an accuracy of ±5‡ and 2% respectively. The measurement accuracies with coefficient of determination (R ² ) of 0.99, for both magnitude (cm.s^-1) and direction (deg.) were achieved.     

Magnetic field configuration of active region NOAA 6555 at the time of a long-duration flare on 23 March 1991 – An Exception to Standard Flare Reconnection Model

The high-resolution H images observed during the decay phase of a long-duration flare on 23 March 1991 are used to study the three-dimensional magnetic field configuration of the active region NOAA 6555. Whereas all the large flares in NOAA 6555 occurred at the location of high magnetic shear and flux emergence, this long-duration flare was observed in the region of low magnetic shear at the photosphere. The H loops activity started soon after the maximum phase of the flare. There were a few long loop at the initial phase of the activity. Some of these were sheared in the chromosphere at an angle of about 45° to the east-west axis. Gradually, an increasing number of shorter loops, oriented along the east-west axis, started appearing. The chromospheric Dopplergrams show blue shifts at the end points of the loops. By using different magnetic field models, we have extrapolated the photospheric magnetograms to chromospheric heights. The magnetic field lines computed by using the potential field model correspond to most of the observed H loops. The height of the H loops were derived by comparing them with the computed field lines. From the temporal evolution of the H loop activity, we derive the negative rate of appearance of H features as a function of height. It is found that the field lines oriented along one of the neutral lines were sheared and low lying. The higher field lines were mostly potential. The paper also outlines a possible scenario for describing the post-flare stage of the observed long-duration flare.     

Application of machine learning techniques in groundwater potential mapping along the west coast of India

ABSTRACT

Groundwater potential mapping (GWPM) in the coastal zone is crucial for the planning and development of society and the environment. The current study is aimed to map the groundwater potential zones of Sindhudurg coastal stretch on the west coast of India, using three machine learning models: random forest (RF), boosted regression tree (BRT), and the ensemble of RF and support vector machine (SVM). In order to achieve the objective, 15 groundwater influencing factors including elevation, slope, aspect, slope length (LS), profile curvature, plan curvature, topographical wetness index (TWI), distance from streams, distance from lineaments, lithology, geomorphology, soil, land use, normalized difference vegetation index (NDVI), and rainfall were considered for inter-thematic correlations and overlaid with spring and well occurrences in a spatial database. A total of 165 spring and well locations were identified, which had been divided into two classes: training and validation, at the ratio of 70:30, respectively. The RF, BRT, and RF-SVM ensemble models have been applied to delineate the groundwater potential zones and categorized into five classes, namely very high, high, moderate, low, and very low. RF, BRT, and ensemble model results showed that 33.3%, 35.6%, and 36.8% of the research area had a very high groundwater potential zone. These models were validated with area under the receiver operating characteristics (AUROC) curve. The accuracy of RF (94%) and hybrid model (93.4%) was more efficient than BRT (89.8%) model. In order to further evaluate and validate, four different sites were subsequently chosen, and we obtained similar results, ensuring the validity of the applied models. Additionally, ground-penetrating radar (GPR) technique was applied to predict the groundwater table and validated by measured wells. The mean difference between measured and GPR predicted groundwater table was 14 cm, which reflected the importance of GPR to guide the location of new wells in the study region. The outcomes of the study will help the decision-makers, government agencies, and private sectors for sustainable planning of groundwater in the area. Overall, the present study provides a comprehensive high-precision machine learning and GPR-based groundwater potential mapping.     

The influence of Southern Hemispheric Equatorial Trough on rainfall during southwest monsoon

Summary Monsoon is a complex dynamical system. Interannual and intraseasonal fluctuations have been studied in the regional and global perspective. Southern Hemispheric Equatorial Trough and its activity during the northern summer appears inversely related to the rainfall activity over the Indian sub-continent in general and Central India in particular. During typical active SHET epochs the rainfall activity becomes deficient in the Central parts of the country. The activity of the SHET is fluctuating in nature. Its duration is prolonged and intensity is increased during the years of major failure.With 2 Figures     

Localization of Branchial Enzymes and their Significance in the Detection of Crude Oil Toxicity in Colisa fasciatus

The effect of crude oil on the histochemical localization of branchial enzymes CA, SDH, LDH, Alkpase and Acidpase was investigated in Colisa fasciatus. The activity of all the enzymes experimented here was found to have decreased when treated with the lethal solutions of crude oil except the LDH which showed an increasing trend throughout the experiment. A transitory increase in the CA and SDH was observed in the beginning but reached an almost normal level after 48 h in 1000 ppm. On the basis of sensitiveness towards crude oil toxicity, the enzymes have been arranged in the following order: LDH > SDH > CA > Alkpase > Acidpase. The results suggest that crude oil is capable of impairing the enzyme activity. The decreased or increased level of enzymes may be used as an indicator for assessing the toxicity of oil pollutants.     

Monsoon rainfall and southern oscillation responses in the pressures over the Northern Indian Ocean

The pressure variations over the North Indian Ocean during the summer monsoon season have been exam-ined using the monthly data from June to September for the period 1961 to 1968. It is found that these varia-tions can be described by two significant eigenvectors (EV1 and EV2) which together account for 53% of the total variance.The first eigenvector (EV1) represents in phase variation over both, the Arabian Sea and the Bay of Bengal with higher variations over the northern side of the area. The second eigenvector (EV2) depicts the out-of-phase variation between the pressure anomalies over the north and the south of 15°N latitude with two areas of pronounced variation, viz., the head Bay of Bengal and the equatorial region near 65°E longitude.The coefficients of EV1 show significant association with rainfall of West Coast and Central India for the concurrent months. These coefficients also show significant association with the pressure and temperature indices of the Southern Oscillation. The coefficients of EV2 show significant association with the monsoon rainfall of south peninsular India.     

Fluid-structure interaction effects for offshore structures

Comprehensive analyses are made of the differences in the responses of simple models of offshore structures computed by the standard and extended versions of Morison's equation for the hydrodynamic forces, and of the effects and relative importance of the numerous parameters involved. The responses also are evaluated by the equivalent linearization technique and Penzien's decoupling technique, and the interrelationship and accuracy of these approaches are elucidated. The results are displayed graphically in the form of response spectra for absolute maximum displacement employing dimensionless parameters that are easy to interpret and use. In addition, the decoupling technique is generalized to include consideration of a current of constant velocity, and a simple modification is proposed which improves the accuracy of this approach. A particularly simple approximation is included for the hydrodynamic modal damping values of multi-degree-of-freedom, stick-like systems.     

El Niño/Southern Oscillation (ENSO) Related Variations in Particulate Export Fluxes in the Western and Central Equatorial Pacific

Time-series data from sediment trap moorings intermittently deployed during 1991–1999 show that the fluxes of biogenic material (carbonate, opal and organic matter, including amino acids) and other related parameters are temporally and spatially distinct across the Western Pacific Warm Pool (WPWP). These variations resulted from the El Niño and La Niña conditions, which alternately prevailed over the equatorial Pacific Ocean during the mooring deployments. The westernmost WPWP (a hemipelagic region) recorded relatively high average total mass and amino acid fluxes during the El Niño event. This was in sharp contrast to the eastern part of the WPWP (oligotrophic and weak upwelling regions) which recorded higher flux values during the La Niña event. Settling particulate organic matter was rich in labile components (amino acids) during La Niña throughout the study area. Relative molar ratios of aspartic acid to β-alanine together with relative molar content of non-protein amino acids β-alanine and γ-aminobutyric acid) suggested that organic matter degradation was more intense during La Niña relative to that during El Niño in the WPWP. This study clearly shows that during an El Niño event the well documented decrease in export flux in the easternmost equatorial Pacific is accompanied by a significant increase in export flux in the westernmost equatorial Pacific Ocean.