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SK Nag 《Journal of the Indian Society of Remote Sensing》1998,26(1-2):69-76
Remote sensing techniques using satellite imagery have proved to be an indispensible tool in morphometric analysis and groundwater studies. In the present area, morphometric analysis using temote sensing techniques have been carried out in Chaka river sub-basin of Manbazar Block, Purulia district, West-Bengal, which is one of the most drought affected area in West-Bengal. The parameters worked out include Bifurcation ratio (Rb), Stream length (Lu). Form factor (Rf), Circulatory ratio (Rc), and Drainage density. The morphometric analysis suggests that the area is covered by fractured, resistant, permeable rocks, the drainage network not so affected by tectonic disturbances. Using satellite imageries of LANDSAT and IRS, different hydrogeomorphological units have been delineated. The study shows that moderately weathered pediplains and valley fills are good prospective zones for groundwater exploration. 相似文献
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Sediment resuspension during and after mechanical excavation of macrophytes may have a significant impact on resident fish populations. Unfortunately, little is known about the influence of this sediment on the respiratory performance and feeding abilities of fishes in New Zealand waterways. We examined the effects of suspended sediment (SS) concentrations previously observed after a large-scale macrophyte removal operation on oxygen consumption (MO2) and feeding rates of brown trout (Salmo trutta). MO2 at 0 mg L?1, 150 mg L?1, 300 mg L?1, 450 mg L?1 and 600 mg L?1 of SS was measured using semi-closed respirometry. Feeding rates at the same SS concentrations were also measured using laboratory tank experiments. Results suggest that SS concentrations up to 600 mg L?1 have no effect on MO2. Conversely, feeding rates were significantly reduced at 450 mg L?1 (22% reduction) and 600 mg L?1 (31% reduction), indicating that sediment concentrations above 450 mg L?1 may negatively affect brown trout populations. 相似文献
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A TEST OF SIGNIFICANCE FOR PARTIAL LEAST SQUARES REGRESSION 总被引：1，自引：0，他引：1
IAN N. WAKELING JEFF J. MORRIS AFRC Institute of Food Research Earley Gate Whiteknights Ro Reading RG EF U.K.Zeneca Pharmaceuticals Mereside Alderley Park Macclesfiel Cheshire SK TG U.K. 《地理学报(英文版)》1993,(4)
Partial least squares (PLS) regression is a commonly used statistical technique for performingmultivariate calibration, especially in situations where there are more variables than samples. Choosingthe number of factors to include in a model is a decision that all users of PLS must make, but iscomplicated by the large number of empirical tests available. In most instances predictive ability is themost desired property of a PLS model and so interest has centred on making this choice based on aninternal validation process. A popular approach is the calculation of a cross-validated r~2 to gauge howmuch variance in the dependent variable can be explained from leave-one-out predictions. Using MonteCarlo simulations for different sizes of data set, the influence of chance effects on the cross-validationprocess is investigated. The results are presented as tables of critical values which are compared againstthe values of cross-validated r~2 obtained from the user's own data set. This gives a formal test forpredictive ability of a PLS model with a given number of dimensions. 相似文献
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SK Pathan VK Shukla RG Patel BR Patel KS Mehta 《Journal of the Indian Society of Remote Sensing》1991,19(2):95-112
Proper urban planning and effective implementation requires reliable urban land use statistics. In this context, satellite remote sensing data has been studied using both visual and digital techniques. A portable eight-band radiometer has been used to collect spectral signatures of surface features present in Ahmedabad city and its environs. Using these signatures a suitable approach employing visual and digital techniques has been developed for urban land use/sprawl mapping. Urban land-use maps of Ahmedabad city and its environs were prepared on 1:25,000 scale and for Ahmedabad Urban Development Authority Area on 1:50,000 scale using this methodology. It has been found that edge-enhancement techniques are useful to enhance the contrast among different urban land uses. Classification techniques such as MXL and Bayes classifiers are not successful in discriminating urban land uses. Tonal characteristics alongwith other elements of interpretation are required to classify urban land uses such as residential, industrial etc. Spatial distribution of various urban and uses and the space devoted to each urban land use has been brought out. 相似文献
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A study of radiosonde observations for temperature at 850 hPa over Delhi for a period of 35 years was conducted. The influence of atmospheric oscillations and geophysical events like El Niño‐Southern Oscillation (ENSO) on tropospheric temperature variability showed indicative trends for changing urban climate in Delhi. The inter‐annual variation in surface temperature and its relationship with land use changes and land cover changes (LULCC) was also examined. LULCC and urban expansion into peripheral areas of Delhi (towards the West, North, North‐West and South) at the cost of agricultural and wasteland was found to be extensive. The upper range of the surface temperature has shifted by ~6°C. The post‐monsoon and winter months from November to February have experienced a considerable increase in the average temperature in the period examined. The monsoon months from June to September have undergone cooling of ~0.5°C–1°C at 850 hPa. An inverse relationship exists between the Southern Oscillation Index (SOI) and the monthly averaged temperature. The temperature of the atmosphere over Delhi at 850 hPa has increased only marginally (~ 0.3°C) for the time period 1980–2015. Bi‐modal peaks were the most peculiar features observed in mean monthly temperature variation during 2000–2009. 相似文献
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Length–weight relationships are a fundamental tool for assessing populations and communities in fisheries science. Many researchers have collected length–weight data throughout New Zealand, yet parameters describing these relationships remain unpublished for many species of freshwater fish. We compiled 285,124 fish records from researchers and institutions across New Zealand to parameterise length–weight equations, using both power and quadratic models, for 53 freshwater species belonging to 13 families. The influence of location and sex on length–weight relationships was also assessed. Location, in particular, generated different length–weight relationships for 65% of the species examined. Length–weight equations were validated by comparing predicted weights against independently measured weights from 25 electrofished sites across New Zealand and the equations were highly accurate (R2>0.99). Recommendations are made about how to robustly apply this new resource which should assist freshwater fisheries researchers throughout New Zealand. 相似文献
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This study was undertaken to prepare an inventory on soil erosion of a hilly river watershed — the Aglar watershed, part of Tehri Garhwal and Dehradun districts (U.P.), using terrain physiography and soil survey data obtained from interpretation and analysis of Landsat TM FCC (1:62,500 scale) and limited ground investigations. The watershed is divided into four broad physiographic units viz. higher Himalayas (> 2000m elevation); lower Himalayas (< 2000m elevation); river terraces and flood plains. Each physiographic unit has been further divided into subunits on the basis of aspects and landuse. Three major orders of soils viz. Inceptisols, Mollisols and Entisols were found in different physiographic units. Soil, and land properties of soilscape units viz. soil depth, texture, structure, slope, landuse and soil temperature regime were evaluated for soil-erosion hazard. The results indicate that in the whole watershed 19.13%, 45.68%, 26.51% and 7.92% areas have been found to be under none to slight, moderate, severe and very severe soil erosion hazard categories, respectively. 相似文献
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Karel ŽÁK Roman SKÁLA Zdeněk ŘANDA Jiří MIZERA 《Meteoritics & planetary science》2012,47(6):1010-1028
Abstract– Tektites, natural silica‐rich glasses produced during impact events, commonly contain bubbles. The paper reviews published data on pressure and composition of a gas phase contained in the tektite bubbles and data on other volatile compounds which can be released from tektites by either high‐temperature melting or by crushing or milling under vacuum. Gas extraction from tektites using high‐temperature melting generally produced higher gas yield and different gas composition than the low‐temperature extraction using crushing or milling under vacuum. The high‐temperature extraction obviously releases volatiles not only from the bubbles, but also volatile compounds contained directly in the glass. Moreover, the gas composition can be modified by reactions between the released gases and the glass melt. Published data indicate that besides CO2 and/or CO in the bubbles, another carbon reservoir is present directly in the tektite glass. To clarify the problem of carbon content and carbon isotopic composition of the tektite glass, three samples from the Central European tektite strewn field—moldavites—were analyzed. The samples contained only 35–41 ppm C with δ13C values in the range from ?28.5 to ?29.9‰ VPDB. This indicates that terrestrial organic matter was a dominant carbon source during moldavite formation. 相似文献
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Suspended sediment (SS) is an important pollutant in freshwater ecosystems and can be detrimental to fish communities. Although macrophytes mediate sediment deposition, little effort has been put into determining how their removal affects sediment resuspension. The present study examined the immediate and long-term impacts of mechanical macrophyte removal on SS concentrations in streams. The results of this study suggest that bed disturbance during mechanical excavation of macrophytes significantly increases SS in the short term, and concentrations were found to increase by as much as 15,687 mg L–1 immediately after macrophyte removal. Significant long-term (77 day) increases in SS were also observed, indicating that without macrophytes, disturbed material is continually resuspended after excavation by fluvial processes. These results demonstrate that macrophyte removal can result in SS levels that have previously been shown to harm fish, and indicate that this activity may be more detrimental to fish than previously thought. 相似文献
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Sujay Dutta NK Patel TT Medhavy SK Srivastava Naveen Mishra KRP Singh 《Journal of the Indian Society of Remote Sensing》1998,26(1-2):7-14
Multi temporal dat acquired at different growth stages increases the dimensionality information content and have advantage over single date data for crop classification. Attempt was made to select suitable single date and combination of multidate data for wheat crop classification in Nalanda district of Bihar state where pulses and other crops are also grown in rabi season. Amongst the single date data February data was found to be better for wheat classification in comparison to November. January, March and April data. Combination of first two principal components each derived from IRS LISS-I four band data acquired in January and February was found to be the best set. Wheat classification accuracy achieved was 94.54 percent. 相似文献
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