Principal component transformation method to separate active discharge and recharge areas     

C V Sundara Rajan  O Batelaan  F De Smedt 《Journal of the Indian Society of Remote Sensing》1997,25(2):93-103

A method is proposed to separate active discharge, recharge and intermediate zones from the digital Thematic Mapper TM data. A case study-was carried out in a natural reserve Welenbos (Walen Forest) and adjacent areas in Belgium comprising a total area of 174:3 sq. km. A microcomputer based Geographic Information and Image Processing System have been utilised for the identification of the characteristic of Remote Sensing TM data favourable for hydrological applications. The histogram of remote sensing data showing the characteristics of discharge, recharge and intermediate zones are unique and can be utilised for mathematical modelling purposes. This has a large potential in hydrological applications.  相似文献   

Geochemistry and petrogenetic evolution of the diatexites of Central Kerala,India     

P K Rajan  M Santosh  K K Ramachandran 《Journal of Earth System Science》1984,93(1):57-69

The hornblende-biotite gneisses of Central Kerala which cover approximately 490km² exhibit schlieric and nebulitic structures, tending towards a homophanous nature and are classified here as diatexites. Mafic protoliths and restite biotite, each representing the refractory residuum of two independent partial melting episodes are widely present in the gneisses. The general mineral assemblage of the gneisses comprise quartz, K-feldspar, oligoclase, biotite and hornblende. Chemically, they are dominantly adamellitic and the behaviour of major and trace elements is consistent with a magmatic parentage. Based on petrochemical criteria, a two-stage evolution model is proposed here, which involves (i) partial melting of mafic granulites under high Archean geothermal gradients and generation of tonalite/trondhjemite through amphibole and plagioclase fractionation and (ii) partial melting and subsequent quartz-alkali feldspar fractionation of the tonalite/trondhjemite under amphibolite facies conditions with synchronous K-enrichment resulting in the diatectic adamellites.  相似文献   

Evidence for relict grains in chondrules of Qingzhen,an E3 type enstatite chondrite     

E.R. Rambaldi  R.S. Rajan  D. Wang  R.M. Housley 《Earth and Planetary Science Letters》1983

Petrographic and chemical studies of the Qingzhen chondrite strongly suggest that it is the most highly unequilibrated (type 3) enstatite chondrite recognized so far. Qingzhen contains abundant, well-defined chondrules, some of which were incompletely molten during the chondrule formation process. The relict olivine grains within these chondrules contain dusty inclusions of almost pure metallic Fe, which appear to be the in-situ reduction product of the fayalitic component of the olivine. The reduction process presumably took place at the time of chondrule formation and the chondrule precursor material must have been more oxidized than average enstatite chondrite material. We believe that this oxidized material may have formed at the enstatite chondrite formation location in the solar nebula, provided fluctuations in the degree of oxidation of the nebular gas existed at such locations. Reheating of this material under more reducing conditions would lead to the observed reduction of the olivine. Igneous olivines within chondrules always contain detectable amounts of CaO, while relict olivines are essentially CaO-free. This seems to suggest that the relict olivines did not originate during a previous igneous process of chondrule formation and might represent condensation products from the early solar nebula.  相似文献   

Space-time variability of low frequency oscillations and Asian summer monsoon precipitation     

Anu Simon  C. K. Rajan  T. N. Krishnamurti 《Meteorology and Atmospheric Physics》2006,93(3-4):177-199

Summary In this study, we provide an observational synthesis of several aspects of MJO (Madden Julian Oscillation) and ISO (Intra Seasonal Oscillation) waves and the manner in which they seem to affect the Asian summer monsoon variability. We examine a number of features such as the passage of MJO waves around the globe from west to east, excitation of ISO waves over the equatorial Indian Ocean, meridional propagation of ISO waves and the role of the local Hadley cell over the monsoon domain in its propagation. The geographical distribution of the amplitude and phase speed of ISO waves over the Asian summer monsoon domain shows that the ISO has prominent centers of action, with small scales of the order of a few 1000 km and that these features vary interannually in amplitude and in their geographical locations. It was also seen that some of the interesting features of the WET and DRY season rainfall distribution can be obtained by compositing the extremes of the amplitude oscillations of these ISO centers. We also noted that the amplitudes of ISO waves generally decay as they propagate north but have an occasional built up in their amplitudes when they seem to encounter and interact with heavy rain producing monsoon disturbances. The issue of these low frequency modes and the modulation of monsoonal dry and wet spells are examined in the context of this broad scenario.  相似文献   

A direct inversion scheme for computing the velocity profile from reflected data     

Bakshi  P. Bianchi  C. Rajan  S. Sivaprasad  K. 《Oceanic Engineering, IEEE Journal of》1987,12(2):433-442

A simple direct inversion scheme for computing the velocity profile of an inhomogeneous slab from reflected data using the order-of-scattering method of solving the Riccati equation for a lossless medium is presented. Extension of this method to the estimation of the constant attention in a low-loss dispersive medium is also indicated.  相似文献   

Trend in Observed and Projected Maximum and Minimum Temperature over N-W Himalayan Basin     

Dharmaveer SINGH  Sanjay K JAIN  Rajan Dev GUPTA 《山地科学学报》2015,(2):417-433

Recently, study in past trends of climate variables gained significant consideration because of its contribution in adaptions and mitigation strategies for potential future changes in climate, primarily in the area of water resource management. Future interannual and inter-seasonal variations in maximum and minimum temperature may bring significant changes in hydrological systems and affect regional water resources. The present study has been performed to observe past(1970-2010) as well as future(2011-2100)spatial and temporal variability in temperature(maximum and minimum) over selected stations of Sutlej basin located in North-Western Himalayan region in India. The generation of future time series of temperature data at different stations is done using statistical downscaling technique. The nonparametric test methods, modified Mann-Kendall test and Cumulative Sum chart are used for detecting monotonic trend and sequential shift in time series of maximum and minimum temperature. Sen’s slope estimator test is used to detect the magnitude of change over a period of time on annual and seasonal basis. The cooling experienced in annual TMax and TMin at Kasol in past(1970-2010) would be replaced by warming in future as increasing trends are detected in TMax during 2020 s and 2050 s and in TMin during 2020 s, 2050 s and 2080 s under A1 B and A2 scenarios. Similar results of warming are also predicted at Sunnifor annual TMin in future under both scenarios which witnessed cooling during 1970-2010. The rise in TMin at Rampur is predicted to be continued in future as increasing trends are obtained under both the scenarios. Seasonal trend analysis reveals large variability in trends of TMax and TMin over these stations for the future periods.  相似文献   

Automatic Tree Identification and Diameter Estimation Using Single Scan Terrestrial Laser Scanner Data in Central Indian Forests     

R. Suraj Reddy  Chandra Shekhar Jha  Krishnan Sundara Rajan 《Journal of the Indian Society of Remote Sensing》2018,46(6):937-943

Forest inventory parameters, primarily tree diameter and height, are required for several management and planning activities. Currently, Terrestrial Laser Scanning (TLS) is a promising technology in automated measurements of tree parameters using dense 3D point clouds. In comparison with conventional manual field inventory methods, TLS systems would supplement field data with detailed and relatively higher degree of accurate measurements and increased measurement frequency. Although, multiple scans from TLS captures more area, they are resource and time consuming to ensure proper co-registration between the scans. On the other hand, Single scans provide a fast and recording of the data but are often affected by occlusions between the trees. The current study evaluates potential of single scan TLS data to (1) develop an automatic method for tree stem identification and diameter estimation (diameter at breast height—DBH) using random sample consensus (RANSAC) based circle fitting algorithm, (2) validate using field based measurements to derive accuracy estimates and (3) assess the influence of distance to scanner on detection and measurement accuracies. Tree detection and diameter measurements were validated for 5 circular plots of 20 m radius using single scans in dry deciduous forests of Betul, Madhya Pradesh. An overall tree detection accuracy of 85 and 70% was observed in the scanner range of 15 and 20 m respectively. The tree detection accuracies decreased with increased distance to the scanner due to the decrease in visible area. Also, estimated stem diameter using TLS was found to be in agreement with the field measured diameter (R² = 0.97). The RMSE of estimated DBH was found to be 3.5 cm (relative RMSE ~20%) over 202 trees detected over 5 plots. Results suggest that single scan approach suffices the cause of accuracy, reducing uncertainty and adds to increased sampling frequency in forest inventory and also implies that TLS has a seemingly high potential in forest management.  相似文献   

Storm surge vulnerability along Chennai–Cuddalore coast due to a severe cyclone THANE     

V. Ranga Rao  B. R. Subramanian  R. Mohan  R. Kannan  T. Mageswaran  T. Arumugam  B. Rajan 《Natural Hazards》2013,68(2):453-465

A very severe cyclonic storm ‘Thane’ developed over the Bay of Bengal during 25–30 December 2011, crossed the Tamilnadu coast between Pondicherry and Cuddalore (southeast coast of India) in early hours of 30 December with a wind speed 120–140 km/h. The offshore tide record reveals that the surge started to generate around 1100 hours on 29 December 2011 with a height 0.4 m and later raised to 0.68 m at the time of land fall, that is, early hours (0000 hours) of 30 December 2011. Field reconnaissance survey on surge run-up and inundation distance at 15 selected locations of cyclone affected areas reveals that the vulnerability levels are highly variable along the coast. The inundation distance extended up to 30–230 m landward from the shoreline and run-up reached to 1.6–3.2 m above chart datum depending upon the cross-shore geometry of the location. In the areas (Verranampattinam, Chinamudaliyar kuppam and Silver beach) near cyclone landfall, the run-up was up to 2.5–3.2 m and the inundation distance extended up to a maximum of 230 m. However, in the areas located about 150 km north of cyclone landfall, the run-up limited from 1.6 to 1.7 m and the inundation distance extended up to only a maximum of 169 m. The inundation distance is mainly influenced by the slope of the beach. In the areas having beach slope between 1 in 135 and 1 in 220, the inundation distance was 210–230 m. However, in the areas having beach slope 1 in 17 to 1 in 34, the inundation distance is restricted between 35 and 50 m.  相似文献   

Geographic information system–based morphometric characterization of sub-watersheds of Meenachil river basin,Kottayam district,Kerala, India     

M.V. Vincy  Brilliant Rajan  A.P. Pradeepkumar 《国际地球制图》2013,28(8):661-684

The study areas Tikovil and Payppara sub-watersheds of Meenachil river cover 158.9 and 111.9 km², respectively. These watersheds are parts of Western Ghats, which is an ecologically sensitive region. The drainage network of the sub-watersheds was delineated using SOI topographical maps on 1:50,000 scale using the Arc GIS software. The stream orders were calculated using the method proposed by Strahler's (1964 Strahler, A. N. 1964. “Quantitative geomorphology of drainage basins and channel networks”. In Hand book of applied hydrology. Vol. 4, Edited by: Chow, V. T. Vol. 4, 39–44.  [Google Scholar]). The drainage network shows that the terrain exhibits dendritic to sub-dendritic drainage pattern. Stream order ranges from the fifth to the sixth order. Drainage density varies between 1.69 and 2.62 km/km². The drainage texture of the drainage basins are 2.3 km^–1 and 6.98 km^–1 and categorized as coarse to very fine texture. Stream frequency is low in the case of Payappara sub-watershed (1.78 km^–2). Payappara sub-watershed has the highest constant of channel maintenance value of 0.59 indicating much fewer structural disturbances and fewer runoff conditions. The form factor value varies in between 0.42 and 0.55 suggesting elongated shape formed for Payappara sub-watershed and a rather more circular shape for Tikovil sub-watershed. The mean bifurcation ratio (3.5) indicates that both the sub-watersheds are within the natural stream system. Hence from the study it can be concluded that GIS techniques prove to be a competent tool in morphometric analysis.  相似文献   

Providing new homes for climate change exiles     

Sujatha Byravan  Sudhir Chella Rajan 《Climate Policy》2013,13(2):247-252

Abstract

Given a certain pre-existing commitment to sea-level rise due to the long thermal lags of the ocean system, several million people living in coastal areas and small islands will inevitably be displaced by the middle of the century. These climate exiles will have nowhere to go. Rather than deal with this in an ad hoc manner as the problem arises, the authors propose a mechanism by which these exiles would be given immigration benefits by countries through a formula that ties numbers of immigrants to a country's historical greenhouse gas emissions. Such a compensatory mechanism appears to be a fair way of addressing the problems faced by climate exiles.  相似文献