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171.
Remote sensing measurements in coral reef environments commonly confront the problem of overlying atmosphere and modification of spectral signal due to water column over the bottom substrates. In order to correct these problems, hyperspectral observations offer an advantage over multispectral observations. Airborne hyperspectral remote sensing data from Airborne Visible Infrared Imaging Spectrometer- Next Generation (AVIRIS-NG) sensor was acquired during low tidal condition on 14 February 2016 at Pirotan reef, Gulf of Kachchh region, India. The objective of this study is to map benthic coverage and bottom topography over Pirotan reef. The methodology involved atmospheric correction, simultaneous retrieval of water parameters, bathymetry, water column correction and mapping. Atmospheric correction was performed by removing path radiance and aerosol contribution and dividing by atmospheric transmittance and incoming solar irradiance to obtain remote sensing reflectance. Model derived error minimization technique was used for simultaneous retrieval of water parameters and bathymetry. Derived water parameters were used to account for water column attenuation and retrieve concomitant true bottom signature. 相似文献
172.
M. R. Ramesh Kumar S. S. C. Shenoi P. Schluessel 《Meteorology and Atmospheric Physics》1999,70(3-4):201-213
Summary The role of the cross equatorial flow from the southern Indian Ocean on the Indian Summer monsoon is examined using the National
Centre for Environmental Prediction (NCEP)/National Centre for Atmospheric Research (NCAR) data for the period January 1982
to December 1994. A comparison of NCEP/NCAR data with the satellite data retrieved from the Special Sensor Microwave Imager
(SSM/I) sensor onboard the Defense Meteorological Satellite Program (DMSP) exhibited a negative bias for the wind speeds greater
than 4 m/s. whereas in the case of specific humidity, SSMI values exhibited a positive bias and the precipitable water derived
from the satellite data exhibited a negative bias. The NCEP reanalysis is able to depict the mean annual cycle of both the
cross equatorial flow and moisture flow into the Indian subcontinent during the monsoon season, but it fails to depict these
differences during excess (1983, 1988, 1994) and deficit monsoon (1982, 1986, 1987) composites. Further, it is seen that inter
hemispheric flow far exceeds the excess moisture available over the Arabian Sea indicating that it is the cross equatorial
flow which decides the fate of the Indian summer monsoon.
Received September 29, 1998 Revised May 20, 1999 相似文献
173.
—The thermodynamic characteristics of the Asian summer monsoon are examined with a global analysis-forecast system. In this study, we investigated the large-scale balances of heat and moisture by making use of operational analyses as well as forecast fields for June, July and August (JJA), 1994. Apart from elucidating systematic errors in the temperature and moisture fields, the study expounds the influence of these errors on the large-scale budgets of heat and moisture over the monsoon region. The temperature forecasts of the model delineate predominant cooling in the middle and lower tropospheres over the monsoon region. Similarly, the moisture forecasts evince a drying tendency in the lower troposphere. However, certain sectors of moderate moistening exist over the peninsular India and adjoining oceanic sectors of the Arabian Sea and Bay of Bengal.¶The broad features of the large-scale heat and moisture budgets represented by the analysis/forecast fields indicate good agreement with the observed aspects of the summer monsoon circulation. The model forecasts fail to retain the analyzed atmospheric variability in terms of the mean circulation, which is indicated by underestimation of various terms of heat and moisture budgets with an increase in the forecast period. Further, the forecasts depict an anomalous diabatic cooling layer in the lower middle troposphere of the monsoon region which inhibits vertical transfer of heat and moisture from the mixed layer of the atmospheric boundary layer to the middle troposphere. In effect, the monsoon circulation is considerably weakened with an increase in the forecast period. The treatment of shallow convection and the use of interactive clouds in the model can reduce the cooling bias considerably. 相似文献
174.
Environmental geochemistry of the Pichavaram mangrove ecosystem (tropical), southeast coast of India 总被引:3,自引:0,他引:3
A. L. Ramanathan V. Subramanian R. Ramesh S. Chidambaram A. James 《Environmental Geology》1999,37(3):223-233
Spatial and temporal geochemical variations of various parameters in the water and sediment of a relatively small mangrove
situated on the southeast coast of India were examined in detail for the first time. The water quality generally reflects
the impact of seawater and the Vellar estuary (mixing effect) aided by evaporation and in situ biological productivity. The
depletion and fluctuation of dissolved silica are controlled by biological processes. Nitrate and phosphate are contributed
by fertilizer input from adjoining agriculture fields. Total suspended matter (TSM) shows an erratic range and trend due to
deforestation and resuspension processes. Sand and silt constitute 70–90% of the sediments. Statistical analysis of the sediments
shows the prevalence of a moderately high-energy environment with very effective winnowing activity. Organic matter content
is higher in the mangrove sediments in comparison to adjacent estuaries. Water and sediment show fluctuations in their chemical
concentration, but no specific trends could be identified. Heavy metals are also enriched in the mangrove sediments, indicating
their unique chemical behavior and the existence of trapping mechanisms. Factor analysis and correlation analysis of water
and sediments show the complexity of the system and the multitude of contributing sources. The core sediment chemistry suggests
the depletion of metal input due to the damming of the detrital inputs. The Pichavaram mangrove seems to be relatively unpolluted,
since the anthropogenic signal observed is small and acts as a sink for heavy metals contributed from a multitude of sources
without an adverse effect.
Received: 5 November 1997 · Accepted: 30 March 1998 相似文献
175.
R. Ramesh 《Journal of Astrophysics and Astronomy》2000,21(3-4):237-240
We present observations of the ‘quiet’ Sun close to the recent solar minimum (Cycle 22), with the Gauribidanur
radioheliograph. Our main conclusion is that coronal streamers also influence the observed radio brightness temperature. 相似文献
176.
V. Ramesh Babu V. S. N. Murty L. V. G. Rao C. V. Prabhu V. Tilvi 《Journal of Earth System Science》2000,109(2):255-265
Hydrographic data collected on board ORV Sagar Kanya in the southern Bay of Bengal during the BOBMEX-Pilot programme (October–November
1998) have been used to describe the thermohaline structure and circulation in the upper 200 m water column of the study region.
The presence of seasonal Inter-Tropical Convergence Zone (ITCZ) over the study area, typically characterized with enhanced
cloudiness and flanked by the respective east/northeast winds on its northern part and west/southwest winds on its southern
part, has led to net surface heat loss of about 55 W/m2. The sea surface dynamic topography relative to 500 db shows that the upper layer circulation is characterised by a cyclonic
gyre encompassing the study area. The eastward flowing Indian Monsoon Current (IMC) between 5‡N and 7‡N in the south and its
northward branching along 87‡E up to 13‡N appear to feed the cyclonic gyre. The Vessel-Mounted Acoustic Doppler Current Profiler
(VM-ADCP) measured currents confirm the presence of the cyclonic gyre in the southern Bay of Bengal during the withdrawing
phase of the southwest monsoon from the northern/central parts of the Bay of Bengal. 相似文献
177.
The forecast of solar cycle (SC) characteristics is crucial particularly for several space-based missions. In the present study, we propose a new model for predicting the length of the SC. The model uses the information of the width of an autocorrelation function that is derived from the daily sunspot data for each SC. We tested the model on Versions 1 and 2 of the daily international sunspot number data for SCs 10?–?24. We found that the autocorrelation width \(A_{\mathrm{w}} ^{n}\) of SC \(n\) during the second half of its ascending phase correlates well with the modified length that is defined as \(T_{\mathrm{cy}}^{n+2} - T_{\mathrm{a}}^{n}\). Here \(T_{\mathrm{cy}}^{n+2}\) and \(T_{ \mathrm{a}}^{n}\) are the length and ascent time of SCs \(n+2\) and \(n\), respectively. The estimated correlation coefficient between the model parameters is 0.93 (0.91) for Version 1 (Version 2) sunspot series. The standard errors in the observed and predicted lengths of the SCs for Version 1 and Version 2 data are 0.38 and 0.44 years, respectively. The advantage of the proposed model is that the predictions of the length of the upcoming two SCs (i.e., \(n+1\), \(n+2\)) are readily available at the time of the peak of SC \(n\). The present model gives a forecast of 11.01, 10.52, and 11.91 years (11.01, 12.20, and 11.68 years) for the length of SCs 24, 25, and 26, respectively, for Version 1 (Version 2). 相似文献
178.
Summary An intercomparison of the characteristic features of the Indian summer monsoon has been carried out for the monsoon months (June to September) of 1995 using the mean monthly analyses/forecasts from the operational centres of ECMWF, JMA, UKMO and NCMRWF. This exercise was undertaken to determine how well the large scale monsoon features over India were reproduced in the operational output in 1995 and also to assess the performance of the NCMRWF assimilation/forecast system. For this purpose, precipitation, mean sea level pressure, circulation features in the lower (850 hPa) and upper (200 hPa) troposphere, mid-tropospheric (500 hPa) temperature, and latent heat flux were examined.It is found that all the dominant features of the Indian summer monsoon are fairly well represented in the analysis and medium range forecasts of the ECMWF, JMA and UKMO. The NCMRWF output agrees well with those from other centres except for a sharp gradient in precipitation across the west coast which was not captured well in the forecasts due to the relatively coarse horizontal resolution of the model compared to that used at other operational centres. Other important features of the southwest monsoon, like the heat low over the northwestern part of the country, the lower level westerly jet and upper level easterly jet etc. are found to be reasonably well represented in the output of all operational centres. The JMA analyses and forecasts possessed greater levels of moisture compared to the NCMRWF output possibly due to the synthetic moisture information used at JMA. The evolution characteristics of the summer monsoon onset over the southern tip of India are found to be comparable in the output of JMA and NCMRWF.With 13 Figures 相似文献
179.
A hydrologic regression sediment-yield model was established to determine the relationship between water discharge and suspended sediment discharge at the Blue Nile and the Atbara River outlet stations during the flood season. The model consisted of two main submodels: (1) a suspended sediment discharge model, which was used to determine suspended sediment discharge for each basin outlet; and (2) a sediment rating model, which related water discharge and suspended sediment discharge for each outlet station. Due to the absence of suspended sediment concentration measurements at or near the outlet stations, a minimum norm solution, which is based on the minimization of the unknowns rather than the residuals, was used to determine the suspended sediment discharges at the stations. In addition, the sediment rating submodel was regressed by using an observation equations procedure. Verification analyses on the model were carried out and the mean percentage errors were found to be +12.59 and –12.39, respectively, for the Blue Nile and Atbara. The hydrologic regression model was found to be most sensitive to the relative weight matrix, moderately sensitive to the mean water discharge ratio, and slightly sensitive to the concentration variation along the River Nile's course. 相似文献
180.
Suganya G. Mary Diviya Deepika B. Madhumitha R. Rajakumari S. Purvaja R. Ramesh R. 《Natural Hazards》2019,98(2):735-750
Natural Hazards - Impacts of coastal processes and anthropogenic activities threaten the archipelago of low-lying reef islands. In this study, long-term (1972–2015) and short-term... 相似文献