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91.
92.
Randhir Singh B. G. Vasudevan P. K. Pal P. C. Joshi 《Journal of Earth System Science》2004,113(1):89-101
Microwave sensor MSMR (Multifrequency Scanning Microwave Radiometer) data onboard Oceansat-1 was used for retrieval of monthly
averages of near surface specific humidity (Q
a) and air temperature (T
a) by means of Artificial Neural Network (ANN). The MSMR measures the microwave radiances in 8 channels at frequencies of 6.6,
10.7, 18 and 21 GHz for both vertical and horizontal polarizations.
The artificial neural networks (ANN) technique is employed to find the transfer function relating the input MSMR observed
brightness temperatures and output (Q
a andT
a) parameters. Input data consist of nearly 28 months (June 1999 – September 2001) of monthly averages of MSMR observed brightness
temperature and surface marine observations ofQ
a
andT
a
from Comprehensive Ocean-Atmosphere Data Set (COADS).
The performance of the algorithm is assessed with independent surface marine observations. The results indicate that the combination
of MSMR observed brightness temperatures as input parameters provides reasonable estimates of monthly averaged surface parameters.
The global root mean square (rms) differences are 1.0‡C and 1.1 g kg−1 for air temperature and surface specific humidity respectively. 相似文献
93.
I. Sadhu Khan D. Lohar D. K. Pal 《Journal of the Indian Society of Remote Sensing》2003,31(4):261-269
Changes in land surface characteristics have become a matter of great concern in the recent years. It is particularly important
when the mesoscale phenomena control the climatic variables of a region. Gangetic West Bengal with its neighbourhood is such
a region where during premonsoon season, mesoscale phenomena, i.e., sea breeze circulation and severe convective development,
control the local climate of the season. It is also reported that a drastic changes in land use pattern has taken place in
recent period over the region, which might affect the local climate, resulting in severe water crisis over the semi-arid part
of the region. A detailed study has been undertaken to investigate the changes in land use pattern through satellite data
over the area and its possible impact on the local climate through numerical modeling. Satellite (IRS-IC and Landsat 4 and
5) data shows a sharp change in dynamic vegetation during this period, which is due to, increased agricultural practices in
the recent years. Mesoscale model indicates that agricultural practices hinder the development of sea breezes over the coastal
and inland places, causing less incursion of moisture towards inland. This may be associated with less number of convective
developments over the coastal and neighbouring places. 相似文献
94.
Béla Paláncz Joseph L. Awange Piroska Zaletnyik Robert H. Lewis 《Journal of Geodesy》2010,84(1):79-95
A fundamental task in geodesy is solving systems of equations. Many geodetic problems are represented as systems of multivariate
polynomials. A common problem in solving such systems is improper initial starting values for iterative methods, leading to
convergence to solutions with no physical meaning, or to convergence that requires global methods. Though symbolic methods
such as Groebner bases or resultants have been shown to be very efficient, i.e., providing solutions for determined systems
such as 3-point problem of 3D affine transformation, the symbolic algebra can be very time consuming, even with special Computer
Algebra Systems (CAS). This study proposes the Linear Homotopy method that can be implemented easily in high-level computer languages like C++ and Fortran that are faster than CAS by at
least two orders of magnitude. Using Mathematica, the power of Homotopy is demonstrated in solving three nonlinear geodetic problems: resection, GPS positioning, and affine
transformation. The method enlarging the domain of convergence is found to be efficient, less sensitive to rounding of numbers,
and has lower complexity compared to other local methods like Newton–Raphson. 相似文献
95.
First Order Seismic Microzonation of Delhi,India Using Geographic Information System (GIS) 总被引:2,自引:4,他引:2
William K. Mohanty M. Yanger Walling Sankar Kumar Nath Indrajit Pal 《Natural Hazards》2007,40(2):245-260
A first order seismic microzonation map of Delhi is prepared using five thematic layers viz., Peak Ground Acceleration (PGA)
contour, different soil types at 6 m depth, geology, groundwater fluctuation and bedrock depth, integrated on GIS platform.
The integration is performed following a pair-wise comparison of Analytical Hierarchy Process (AHP), wherein each thematic
map is assigned weight in the 5-1 scale: depending on its contribution towards the seismic hazard. Following the AHP, the
weightage assigned to each theme are: PGA (0.333), soil (0.266), geology (0.20), groundwater (0.133) and bedrock depth (0.066).
The thematic vector layers are overlaid and integrated using GIS. On the microzonation theme, the Delhi region has been classified
into four broad zones of vulnerability to the seismic hazard. They are very high (> 52%), high (38–52%), moderate (23–38%)
and less ( < 23%) zones of seismic hazard. The “very high” seismic hazard zone is observed where the maximum PGA varies from
140 to 210 gal for a finite source model of Mw 8.5 in the central seismic gap. A site amplification study from local and regional earthquakes for Delhi region using Delhi
Telemetry Network data shows a steeper site response gradient in the eastern side of the Yamuna fluvial deposits at 1.5 Hz.
The ‘high’ seismic hazard zone occupies most of the study area where the PGA value ranges from 90 to 140 gal. The ‘moderate’
seismic hazard zone occurs on either side of the Delhi ridge with PGA value varying from 60 to 90 gal. The ‘less’ seismic
hazard zone occurs in small patches distributed along the study area with the PGA value less than 60 gal. Site response studies,
PGA distribution and destruction pattern of the Chamoli earthquake greatly corroborate the seismic hazard zones estimated
through microzonation on GIS platform and also establishes the methodology incorporated in this study. 相似文献
96.
The paper presents the seasonal variation of 6300 Å line intensity at Calcutta with relative sunspot number, solar flare number and variable component of 10.7 cm solar flux. A study has been made and important results have been obtained which are as follows. (i) Intensity of 6300 Å line shows periodic variation with relative sunspot number, solar flare number and variable component of 10.7 cm solar flux during the period 1984–1986 which is the secondary peak of the descending phase of 21st solar cycle. (ii) 6300 Å line intensity at Cachoeira Paulista station, taken by Sahai et al. (1988), also shows periodic variation with solar parameters during the period 1978–1980 which is the peak phase of the solar cycle. (iii) A possible explanation of such a type of variation is also presented. 相似文献
97.
An attempt is made to search for a consistent model to explain the electromagnetic spectrum of the Crab nebula (Tau A). It is assumed that there is a continuous injection of electrons at the centre of the nebula with an energy spectrumE
–1.54 as evidenced by radio data. This spectrum must steepen to a slope larger than 2 at some energyE
i
in order to ensure that the energy input into electrons remains finite. The spectrum must also steepen beyond an energyE
c
depending on the magnetic field because of synchrotron energy losses. Two types of models are considered: Class I, in which the whole nebula is characterised by a uniform magnetic field, and Class II, in which besides the general fieldH
0, small filamentary regions of strong fieldH
s
are postulated.In models of Class I, the best fit to the observed data is obtained whenE
t
>E
c
andH
05×10–4 gauss. However, this predicts a decrease in X-ray source size beyond 40 KeV. There are two possibilities of Class II model depending on the residence time of electrons in strong field regions being small or large. The former case explains the flattening in the optical spectrum.Experiments to distinguish between the various models are indicated.Presented at the International Conference on Cosmic Rays, Budapest, 1969. 相似文献
98.
99.
S. K. Deb Inderpreet Kaur C. M. Kishtawal P. K. Pal 《Theoretical and Applied Climatology》2014,115(3-4):693-702
The operational derivation of atmospheric motion vectors (AMVs) using infrared (10.5–12.5 μm) and water vapor (6.3–7.1 μm) channels of successive geostationary satellite images started in the 1980s. Subsequently, AMVs have become an important component for operational numerical weather prediction throughout the globe for the last decade or so. In India, at the Space Applications Centre, Indian Space Research Organisation, the operational derivation of AMVs (infrared winds and water vapor winds) from the Indian geostationary satellite Kalpana-1 has been initiated a few years back. Recently, an L-band radar lower atmosphere wind profiler (LAWP) has been installed at the National Atmospheric Research Laboratory, Gadanki located at (13.58°N, 79.28°E) for continuous high-resolution wind measurements in the lower atmosphere. In this study, a comparison of Kalpana-1 AMVs with wind measurements from LAWP and radiosonde has been carried out for a period of one and a half years. The performances of Kalpana-1 AMVs are also assessed by a separate comparison of Meteosat-7 AMVs, derived at the European Organisation for the Exploitation of Meteorological Satellites, with wind measurements from LAWP and radiosonde. Both sets of comparison show that AMVs from Kalpana-1 and Meteosat-7 are comparable over the Indian Ocean region. 相似文献
100.
Climate change has the potential ability to alter the occurrence and severity of extreme events. Though predicting changes
of such extreme events is difficult, understanding them is important to determine the impacts of climate change in various
sectors. This paper presents the change in rainfall extremes in the monsoon season in south-west Indian peninsula. Daily rainfall
data were analysed for the entire Kerala state in India to determine if the extreme rainfall had changed over the 50-year
period. Several indices were derived from the data to identify the extreme rainfalls. The trends of all the extreme indices
were assessed by parametric ordinary least square regression technique, which were tested for significance at 95% level. Results
showed significant decrease in monsoon rainfall extremes in Kerala that would affect the tendency of change in seasonal total
rainfall. This study provides a comprehensive knowledge on extreme monsoon precipitation in Kerala, which could also be employed
to study changing climate at local scale in other regions. 相似文献