排序方式： 共有7条查询结果，搜索用时 62 毫秒
1
1.
T. Roy Choudhury Kanan Datta Suman Majumdar Raghunath Ghara Aseem Paranjape Rajesh Mondal Somnath Bharadwaj Saumyadip Samui 《Journal of Astrophysics and Astronomy》2016,37(4):29
Studying the cosmic dawn and the epoch of reionization through the redshifted 21-cm line are among the major science goals of the SKA1. Their significance lies in the fact that they are closely related to the very first stars in the Universe. Interpreting the upcoming data would require detailed modelling of the relevant physical processes. In this article, we focus on the theoretical models of reionization that have been worked out by various groups working in India with the upcoming SKA in mind. These models include purely analytical and semi-numerical calculations as well as fully numerical radiative transfer simulations. The predictions of the 21-cm signal from these models would be useful in constraining the properties of the early galaxies using the SKA data. 相似文献
2.
Comparison of Two Data Smoothing Techniques for Vegetation Spectra Derived From EO-1 Hyperion 总被引：1，自引：0，他引：1
Anshu Miglani Shibendu S. Ray D. P. Vashishta Jai Singh Parihar 《Journal of the Indian Society of Remote Sensing》2011,39(4):443-453
Hyperspectral data are generally noisier compared to broadband multispectral data because their narrow bandwidth can only
capture very little energy that may be overcome by the self-generated noise inside the sensors. It is desirable to smoothen
the reflectance spectra. This study was carried out to see the effect of smoothing algorithms - Fast-Fourier Transform (FFT)
and Savitzky–Golay (SG) methods on the statistical properties of the vegetation spectra at varying filter sizes. The data
used in the study is the reflectance spectra data obtained from Hyperion sensor over an agriculturally dominated area in Modipuram
(Uttar Pradesh). The reflectance spectra were extracted for wheat crop at different growth stages. Filter sizes were varied
between 3 and 15 with the increment of 2. Paired t-test was carried out between the original and the smoothed data for all the filter sizes in order to see the extent of distortion
with changing filter sizes. The study showed that in FFT, beyond filter size 11, the number of locations within the spectra
where the smooth spectra were statistically different from its original counterpart increased to 14 and reaches 21 at the
filter size 15. However, in SG method, number of statistically different locations were more than those found in the FFT,
but the number of locations did not changing drastically. The number of statistically disturbed locations in SG method varied
between 16 and 19. The optimum filter size for smoothing the vegetation spectra was found to be 11 in FFT and 9 in SG method. 相似文献
3.
Anshu Miglani S. S. Ray R. Pandey J. S. Parihar 《Journal of the Indian Society of Remote Sensing》2008,36(3):255-266
The present study was carried out to evaluate the satellite-based hyperspectral data available from Hyperion onboard EO-1
of NASA for agricultural applications. The study was carried out for Daurala block of Meerut district, using data of March
2005. The preliminary data analysis showed that there are 196 usable bands out of a total of 242 bands. Principal component
(PC) analysis showed that about 99% of the information explained in 10 PCs. The atmospherically corrected reflectance, derived
from satellite data had good agreement with the ground reflectance, observed using handheld spectroradiometer, with r2 ranging from 0.85 to 0.98. A set of twenty most usable bands was selected by the criteria of maximum contribution to first
five PCs and the band combinations with least inter-band correlations. 相似文献
4.
Pristine mountain environments are more sensitive to climate change than other land surfaces. Climatic variations in mountainous terrain are still poorly understood. Previous studies revealed inconsistent findings on the elevational dependence of warming in the mountains. In this study, the trends and elevational dependence of air temperature in the Cariboo Mountains Region (CMR) of British Columbia are explored using a surface air temperature dataset with a spatial resolution of five arc minutes over the 1950–2010 period. A Mann-Kendall test is performed for evaluation of trends and their significance. In recent decades the CMR has been warming at a faster rate than regional and global warming. The minimum air temperature trend shows significant amplified warming at higher elevations. The snow–albedo feedback and changes in cloud cover over the CMR may possibly be the major physical mechanisms responsible for these trends. The implications of such changes on the endangered mountain caribou and water resources of the area are also discussed. 相似文献
5.
Eigenvalue approach, following Laplace and Fourier transforms, has been employed to find the general solution to the field
equations in an anisotropic liquid-saturated porous medium, in the transformed domain. The results of isotropic liquid-saturated
porous medium can be derived as a special case. A numerical inversion technique has been applied to get the solutions in the
physical domain. To illustrate the utility of the approach, an application of infinite space with impulsive force at the origin
has been considered. The results in the form of displacement and stress components have been obtained and discussed graphically
for a particular model. 相似文献
6.
Variability and trends in runoff in the rivers of British Columbia's Coast and Insular Mountains 
下载免费PDF全文
下载免费PDF全文 This study examines the 1914–2015 runoff trends and variability for 136 rivers draining British Columbia's Coast and Insular Mountains. Rivers are partitioned into eastward and westward flowing rivers based on flow direction from the Coast Mountains. Thus, eastward and westward runoff trends and influence of topography on runoff are explored. Our findings indicate that rivers flowing eastward to the Nechako and Chilcotin plateaus contribute the lowest annual runoff compared to westward rivers where runoff is high. Low interannual runoff variability is evident in westward rivers and their alpine watersheds, whereas eastward rivers exhibit high interannual runoff variability. On Vancouver Island, some of the rivers with the highest annual runoff exhibit high interannual variability. A significant (p < .05) negative correlation exists between mean annual runoff (Rm) and latitude, gauged area, mean elevation, and its corresponding coefficient of variation. However, a significant positive correlation was found between the glacierized area of mountainous regions and Rm. The mean coefficient of variation in annual runoff is significantly negatively correlated with latitude and glacierized area, but significantly positively correlated with longitude. Annual and seasonal runoff trend analyses of each river were performed for an early (1936–2015), a middle (1966–2015), and a late (1986–2015) period using the Mann–Kendall test. Trend analyses revealed a shift towards more positive detectable (signal‐to‐noise ratio > 1) trends in annual and seasonal runoff from the middle to the late period across the study domain. Most positive detectable seasonal runoff trends in the middle period occur in spring in glacierized westward rivers located >1,200 m, whereas in the late period, they all occur in fall and are regionally coherent around Vancouver Island and south coastal BC. Rivers draining eastward exhibit more positive trends over 1986–2015 compared to westward rivers. This study provides crucial information on the hydrology of mountain watersheds across British Columbia's coast in response to Pacific Decadal Oscillation phase changes, the elevational amplification of regional climate change, and their influences on precipitation and glacier retreat. 相似文献
7.
A plain strain problem of an isotropic elastic liquid-saturated porous medium in poroelasticity has been studied. The eigenvalue
approach using the Laplace and Fourier transforms has been employed and these transforms have been inverted by using a numerical
technique. An application of infinite space with concentrated force at the origin has been presented to illustrate the utility
of the approach. The displacement and stress components in the physical domain are obtained numerically. The results are shown
graphically and can be used for a broad class of problems related to liquid-saturated porous media. 相似文献
1