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21.
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
22.
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
23.
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
24.
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
25.
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
26.
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
27.
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
28.
The sedimentary history of Kachchh offshore (central western Indian margin), especially since the eruption of the Deccan Traps (∼65 Ma), has remained scantily studied despite an area with promising resource potential. Of late, new marine surveys combined with industrial drilling along the Kachchh shelf are beginning to elucidate the depositional history of this region. Here, we attempt to synthesize interpretation of new offshore seismic data, along with borehole information and long-term sea-level variations to provide a coherent sedimentological and lithostratigraphic framework over the past ∼65 Ma in this area. 相似文献
29.
Details are presented of a methodology that utilizes acoustic travel time information in an ocean circulation model. Recent developments of this model-oriented tomography are discussed, representing some significant improvements over earlier formulations. More accurate means of determining the arrival times of specific ray paths are detailed, along with a means of estimating possible errors in the calculated travel times. The assimilation of the observed arrival time information into an ocean model is achieved using a Kalman gain, and more advanced expressions for calculating the Kalman gain are presented. A formulation to account for errors in the stated positions of a source and receiver is also presented. It is shown that the methodology performs fairly well in reproducing observed travel time anomalies. However, the model-predicted anomalies along a specific ray path may not always track the observed anomalies for that path when assimilating multiple ray path data. Results indicate that additional work is required to determine a means of handling observed arrival time data without having prior knowledge of the magnitude of errors in the observations. Results from simulation experiments provide estimates of: (1) potential errors when the travel times for ray paths are only sampled at discreet intervals as opposed to continuously and (2) to what degree acoustic data can be expected to “correct” model-predicted fields. 相似文献
30.
There is a large thermal contrast between the Arabian Peninsula and India (Δθ AI) at the mature stage of the Indian summer monsoon (ISM). The forming process of Δθ AI is investigated analyzing various datasets. It forms earlier in the lower troposphere than in the middle and upper layers. The potential temperature in the lower troposphere over the west coast of India (θ IW) abruptly decreases in advance of the rapid enhancement of the westerly wind over the Arabian Sea corresponding to the ISM onset. Such a process was observed for all the target years and the rapid decrease in θ IW could trigger the ISM onset. The decrease in θ IW had two patterns. In one case, cooler air is brought by the strong winds around a cyclone over the Arabian Sea. In another case, θ IW decreases gradually by a synergy of a southwesterly wind over the Arabian Sea and the enlargement of Δθ AI. 相似文献