A global map of rainfed cropland areas (GMRCA) at the end of last millennium using remote sensing     

Chandrashekhar M. Biradar  Prasad S. Thenkabail  Praveen Noojipady  Yuanjie Li  Venkateswarlu Dheeravath  Hugh Turral  Manohar Velpuri  Murali K. Gumma  Obi Reddy P. Gangalakunta  Xueliang L. Cai  Xiangming Xiao  Mitchell A. Schull  Ranjith D. Alankara  Sarath Gunasinghe  Sadir Mohideen 《International Journal of Applied Earth Observation and Geoinformation》2009

The overarching goal of this study was to produce a global map of rainfed cropland areas (GMRCA) and calculate country-by-country rainfed area statistics using remote sensing data. A suite of spatial datasets, methods and protocols for mapping GMRCA were described. These consist of: (a) data fusion and composition of multi-resolution time-series mega-file data-cube (MFDC), (b) image segmentation based on precipitation, temperature, and elevation zones, (c) spectral correlation similarity (SCS), (d) protocols for class identification and labeling through uses of SCS R²-values, bi-spectral plots, space-time spiral curves (ST-SCs), rich source of field-plot data, and zoom-in-views of Google Earth (GE), and (e) techniques for resolving mixed classes by decision tree algorithms, and spatial modeling. The outcome was a 9-class GMRCA from which country-by-country rainfed area statistics were computed for the end of the last millennium. The global rainfed cropland area estimate from the GMRCA 9-class map was 1.13 billion hectares (Bha). The total global cropland areas (rainfed plus irrigated) was 1.53 Bha which was close to national statistics compiled by FAOSTAT (1.51 Bha). The accuracies and errors of GMRCA were assessed using field-plot and Google Earth data points. The accuracy varied between 92 and 98% with kappa value of about 0.76, errors of omission of 2–8%, and the errors of commission of 19–36%.  相似文献   

Seismic attribute study for gas hydrates in the Andaman Offshore India   总被引：1，自引：0，他引：1  

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   

Spectral characteristics of high shallow water waves     

V. Sanil Kumar  K. Ashok Kumar 《Ocean Engineering》2008,35(8-9):900-911

The spectral characteristics of shallow water waves with significant wave height more than 2 m based on the data collected along the Indian coast is examined. It was found that the value of Joint North Sea Wave Project (JONSWAP) parameters (α and γ) increases with significant wave height and mean wave period and decreases with spectral peak period. The estimated average value (0.0027 and 1.63) of the JONSWAP parameters, α and γ were less than the generally recommended values of 0.0081 and 3.3, respectively. By carrying out a multi-regression analysis, an empirical equation is arrived relating the JONSWAP parameters with significant wave height, peak wave period and mean wave period. It was found that the Scott spectra underestimate the maximum spectral energy of high waves. The study shows that the measured wave spectra can be represented by JONSWAP spectra with the JONSWAP parameters estimated based on the equation proposed in this paper.  相似文献   

GIS based spatial data analysis for landslide susceptibility mapping   总被引：5，自引：4，他引：1  

S. Sarkar  D. P. Kanungo  A. K. Patra  Pushpendra Kumar 《山地科学学报》2008,5(1):52-62

Landslide susceptibility map delineates the potential zones for landslides occurrence. The paper presents a statistical approach through spatial data analysis in GIS for landslide susceptibility mapping in parts of Sikkim Himalaya. Six important causative factors for landslide occurrences were selected and corresponding thematic data layers were prepared in GIS. Topographic maps,satellite image,field data and published maps constitute the input data for thematic layer preparation. Numerical weights for different categories of these factors were determined based on a statistical approach and the weighted thematic layers were integrated in GIS environment to generate the landslide susceptibility map of the area. The landslide susceptibility map classifies the area into five different landslide susceptible zones i.e.,very high,high,moderate,low and very low. This map was validated using the existing landslide distribution in the area.  相似文献   

Species diversity and population status of threatened plants in different landscape elements of the Rohtang Pass,western Himalaya     

K. N. Singh  Gopichand  Amit Kumar  Brij Lal  N. P. Todaria 《山地科学学报》2008,5(1):73-83

This paper highlights the quantitative estimates of plant species diversity and ecosystems of the Rohtang Pass,which is one of the most preferred visiting spots by tourists in Himachal Pradesh （H.P.）,India. In spite of high pressure of anthropogenic activities,the Rohtang Pass still harbours a variety of flowering plants with economic value,including various medicinal herbs. In order to observe species diversity in different landscape elements （LSEs）,ground surveys were conducted in nine unique LSEs within the elevation range between 3624 m and 4332 m. Plant community structure in each LSE was studied using stratified random sampling where a total 56 quadrats of 1 m^2 in size for herbs and 7 quadrats of 25 m^2 for shrubs were made. Of the total 50 plant species belonging to 15 families recorded in different random quadrats,24 species were found of medicinal value. Maximum species richness （18） and value of Shannon diversity （H＇=2.2648） were observed on northeast-facing slope in Picrorhiza kurrooa dominated LSE in moist area,followed by Rheum emodi LSE （species richness = 17 and H＇ = 2.4141） distributed on south-facing slope. Maximum values of species richness and Shannon diversity in Rheum emodi LSE were observed between 8 ～ 12 and 1.4797 ～ 2.1911,respectively. Rhododendron anthopogon dominated LSE on northwest-facing slope was found least diverse in terms of species richness where the Simpson index of dominance （D） was 0.4205. The species were equal in abundance in P. kurrooa LSE on east-facing slope and Pleurospermum candollii LSE on north-facing slope,showing the maximum similarity in terms of species distribution between the two LSEs. Low turnover of species across common LSEs gives an idea regarding their limited distribution. Five species of threatened category according to the IUCN criteria were observed in seven LSEs. The largest population of threatened medicinal plants was recorded on northeast and northwest-facing slopes where population density of Bergenia stracheyi （  相似文献   

Growth of Prosopis juliflora on pegmatite tailings from Nellore Mica Belt, Andhra Pradesh, India     

A. Nagaraju  K. S. S. Prasad 《Environmental Geology》1998,36(3-4):320-324

 Prosopis juliflora was found to be occurring extensively on the pegmatitic tailings. Leaves and twigs of P. juliflora and soil samples were analyzed for mineral elements. The analysis has shown variation in the absorption and accumulation of mineral elements of the same plant species growing at different areas. The plant species accumulated large concentrations of Sr, B, and Ba. The ubiquitous thorny shrub P. juliflora has an extraordinary ecologic amplitude and tolerance for a variety of elements. Received: 10 October 1997 · Accepted: 13 January 1998  相似文献   

Linear stability and the resonance cases for the triangular libration points for the doubly photo-gravitational elliptic restricted problem of three bodies     

Kumar  V.  Choudhry  R. K. 《Celestial Mechanics and Dynamical Astronomy》1989,46(1):59-77

In the present paper we have found the range of values of μ ande for the linear stability of the triangular points for the doubly photogravitational elliptic restricted problem of three bodies. It has been shown that some resonances of the third and the fourth order exist which will need special investigation for the determination of complete stability of the libration points under our terms of reference.  相似文献   

Basin‐scale stream‐flow forecasting using the information of large‐scale atmospheric circulation phenomena     

Rajib Maity  D. Nagesh Kumar 《水文研究》2008,22(5):643-650

It is well recognized that the time series of hydrologic variables, such as rainfall and streamflow are significantly influenced by various large‐scale atmospheric circulation patterns. The influence of El Niño‐southern oscillation (ENSO) on hydrologic variables, through hydroclimatic teleconnection, is recognized throughout the world. Indian summer monsoon rainfall (ISMR) has been proved to be significantly influenced by ENSO. Recently, it was established that the relationship between ISMR and ENSO is modulated by the influence of atmospheric circulation patterns over the Indian Ocean region. The influences of Indian Ocean dipole (IOD) mode and equatorial Indian Ocean oscillation (EQUINOO) on ISMR have been established in recent research. Thus, for the Indian subcontinent, hydrologic time series are significantly influenced by ENSO along with EQUINOO. Though the influence of these large‐scale atmospheric circulations on large‐scale rainfall patterns was investigated, their influence on basin‐scale stream‐flow is yet to be investigated. In this paper, information of ENSO from the tropical Pacific Ocean and EQUINOO from the tropical Indian Ocean is used in terms of their corresponding indices for stream‐flow forecasting of the Mahanadi River in the state of Orissa, India. To model the complex non‐linear relationship between basin‐scale stream‐flow and such large‐scale atmospheric circulation information, artificial neural network (ANN) methodology has been opted for the present study. Efficient optimization of ANN architecture is obtained by using an evolutionary optimizer based on a genetic algorithm. This study proves that use of such large‐scale atmospheric circulation information potentially improves the performance of monthly basin‐scale stream‐flow prediction which, in turn, helps in better management of water resources. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Correlation between magnetic shear and magnetic tension in a solar active region     

P. Venkatakrishnan  R. S. Narayanan  N. D. N. Prasad 《Solar physics》1993,144(2):315-322

The difference between the magnetic tension and magnetic shear was calculated for four vector magnetograms of NOAA AR 4474. It was seen that this difference between the two independent angular measures of magnetic stress is less than 18° for more than 50% of the pixels. Magnetic tension is thus found to be fairly well correlated with magnetic shear for AR 4474.  相似文献   

Soret effects on free-convection and mass transfer flow in the stokes problem for a infinite vertical plate     

JHA Basant Kumar  A. K. Singh 《Astrophysics and Space Science》1990,173(2):251-255

An analytical study is performed to examine the free-convection and mass transfer flow for the Sokes problem for an infinite vertical plate on taking into account the Soret effect (thermal diffusion effect). The Laplace transform technique is used to obtain the expressions for velocity and skin-friction. The effect of Soret numberS on velocity field and skin-friction is extensively discussed with the help of graphs and table.  相似文献