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1.
Purvee Joshi Sandip R. Oza Ujjwal K. Gupta Shailendra Saini D. Ram Rajak I. M. Bahuguna 《Marine Geodesy》2020,43(3):302-323
AbstractIntra and inter-annual variations in the sea ice thickness are highly sensitive indicators of climatic variations undergoing in the earth’s atmosphere and oceans. This paper describes the method of estimating sea ice thickness using radar waveforms data acquired by SARAL/Altika mission during its drifting orbit phase from July 2016 onwards yielding spatially dense data coverage. Based on statistical analysis of return echoes, classification of the surface has been carried out in three different types, viz. floe, lead and mixed. Time delay correction methods were suitably selected and implemented to make corrections in altimetric range measurements and thereby freeboard. By assuming hydrostatic equilibrium, freeboard data were converted into sea ice thickness. Results show that sea ice thickness varies from 4 to 5?m near ice shelves and 1 to 2.5?m in the marginal sea ice regions. Freeboard and sea ice thickness estimates were also validated using NASA’s Operation Ice Bridge (OIB) datasets. Freeboard measurements show very high correlation (0.97) having RMSE of 0.13. Overestimation of approximately 1–2?m observed in the sea ice thickness, which could be attributed to distance between AltiKa footprint and OIB locations. Moreover, sensitivity analysis shows that snow depth and snow density over sea ice play crucial role in the estimation of sea ice thickness. 相似文献
2.
Daily zenith scattered light intensity observations were carried out in the morning twilight hours using home-made UV-visible
spectrometer over the tropical station Pune (18‡31′, 73‡51′) for the years 2000–2003. These observations are obtained in the
spectral range 462–498 nm for the solar zenith angles (SZAs) varying from 87‡ to 91.5‡. An algorithm has been developed to
retrieve vertical profiles of ozone (O3) and nitrogen dioxide (NO2) from ground-based measurements using the Chahine iteration method. This retrieval method has been checked using measured
and recalculated slant column densities (SCDs) and they are found to be well matching. O3 and NO2 vertical profiles have been retrieved using a set of their air mass factors (AMFs) and SCDs measured over a range of 87–91.5‡
SZA during the morning. The vertical profiles obtained by this method are compared with Umkehr profiles and ozonesondes and
they are found to be in good agreement. The bulk of the column density is found near layer 20–25 km. Daily total column densities
(TCDs) of O3 and NO2 along with their stratospheric and tropospheric counterparts are derived using their vertical profiles for the period 2000–2003.
The total column, stratospheric column and tropospheric column amounts of both trace gases are found to be maximum in summer
and minimum in the winter season. Increasing trend is found in column density of NO2 in stratospheric, tropospheric and surface layers, but no trend is observed in O3 columns for above layers during the period 2000–2003 相似文献
3.
The day-to-day variations in ozone content at Uccle (51oN) during some stratospheric warming events are ex-amined. In particular, the attention is focused on the timing of commencement of ozone enhancement prior to peak day of warming and on the relationship in the ozone content between the upper and lower stratosphere. These two features are compared with the predictions of ozone transport models. There seems to be an agreement between mod-el predictions and observed features in some cases. 相似文献
4.
The island city of Bombay is surrounded by Thane creek in the east and Ulhas river on the north. These two aquatic regimes act as receptacles of industrial waste and sewage discharges from the city and also lithogenic fluxes from the adjacent basaltic terrain.
Two consecutive sets of pre-monsoon and post-monsoon samples of water, suspended solids and sediments were collected from the intertidal zone of Thane Creek and along the Ulhas River. These were analysed for toxic heavy metals such as Fe. Mn, Ni, Co, Pb, Zn, Cu, Cr, Hg and Cd and the degree of metal contamination was determined. Using this data the pattern and mechanism of distribution of heavy metals in water, suspended solids and sediments were investigated. These are closely related to discharges of industrial effluents and domestic sewage and largely controlled by basic geochemical processes. 相似文献
5.
Organotins, especially tributyltins (TBT) are highly toxic to many marine organisms. These compounds are introduced in marine waters by ship trafficking, ship scrapping activities, as antifouling compounds and sewage disposal. Marine fishes, crustaceans and molluscans are easily prone to organotins contamination. In view of this, a baseline monitoring study was conducted in order to establish the levels of organotins in edible marine fishes, bivalves, shrimps, squids and crabs collected from Mumbai, Goa and Karwar on the west coast of India. At these locations average organotin concentration found in fishes, clams, shrimps, squids and crabs was 108, 852, 179, 70 and 89 ng Sn g−1 dw, respectively. In all the samples butyltins dominated over phenyltins. The levels of organotins suggest that all the organisms were contaminated with organotins and their consumption may pose health problems to humans. 相似文献
6.
R. M. Samudraiah Desu Ashutosh Kumar Jha Senthil Kumar Arumugam V. N. Krishna Murthy Yelisetty Ujjwal Kumar Kusum Arunachalam 《Journal of the Indian Society of Remote Sensing》2018,46(6):895-902
Ocean colour sensors traditionally are of fixed spectral channel systems with specified bandwidth of about 20 nm in the visible region and about 40 nm in Near Infrared region. In these systems, it is known that a radiometric error of 1% in the measurement of top of the atmosphere signal may lead to an error of 10% in the retrieved ocean upwelling radiance. In this paper we investigated the range of wavelengths participating in signal collection (effective spectral pass band, ESPB) using relative spectral response data of various sensors flown earlier. ESPB values were computed for each spectral channel for various percentages of signal and the results showed that they are quite high compared to bandwidths specified. These values were found to vary with sensor and channel. ESPB shall be small for accurate computation of spectral radiance. As the knowledge of spectral profile of the signal in the range of ESPB helps in better estimation of spectral radiance at the intended wavelengths, a miniature high performance linear variable filter based hyperspectral sensor is proposed as an alternative. We present here the design concept and report the estimated performance of such sensor that can be realized even with commercial off the shelf components for operational implementation. 相似文献
7.
Soma Mukherjee Ujjwal Bhattacharya S. K. Parui Ranjan Gupta Ravi K. Gulati 《Astrophysics and Space Science》1996,239(2):361-373
In this paper we present an application of an artificial neural network model based on a multi-layered backpropagation algorithm for spectral classification of UV data from the International Ultraviolet Explorer (IUE) low dispersion spectra reference atlas. The model used is similar to that of von Hippel et al. (1994), and is found to reduce the classification error as compared to the recently reported results on the same data set (Gulati et al. 1994b). The improved version of the network is much simpler in structure and the training time is reduced by a factor of almost 20. Such networks will prove very useful in efficient classification of large databases
Subject headings: neural networks, stellar spectra, classification 相似文献
8.
The island city of Bombay is surrounded by Thane Creek in the east and the Ulhas River to the north. These two aquatic regimes act as receptacles of industrial and sewerage discharges from the city and also lithogenic fluxes from the adjacent basaltic terrain.
Two consecutive sets of pre-monsoon and post-monsoon samples of water, suspended solids and sediments were collected from nineteen stations along the intertidal zone of Thane Creek and from eleven stations along the Ulhas River course. Toxic heavy metals such as Fe, Mn, Ni, Co, Pb, Zn, Cu, Cr, Hg and Cd have been analysed in the samples and the degree of metal contamination has been brought out by comparison with local background as well as global standards. Thane Creek is relatively stagnant and dominated by a marine environment, while the Ulhas River is more dynamic and fluvio-estuarine in nature. The two environmental settings have been recognised in discriminant analysis of the heavy metal data. 相似文献
9.
ARIMA forecasting of ambient air pollutants (O3, NO, NO2 and CO) 总被引：1，自引：0，他引：1
Ujjwal Kumar V. K. Jain 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(5):751-760
In the present study, a stationary stochastic ARMA/ARIMA [Autoregressive Moving (Integrated) Average] modelling approach has
been adapted to forecast daily mean ambient air pollutants (O3, CO, NO and NO2) concentration at an urban traffic site (ITO) of Delhi, India. Suitable variance stabilizing transformation has been applied
to each time series in order to make them covariance stationary in a consistent way. A combination of different information-criterions,
namely, AIC (Akaike Information Criterion), HIC (Hannon–Quinn Information Criterion), BIC (Bayesian Information criterion),
and FPE (Final Prediction Error) in addition to ACF (autocorrelation function) and PACF (partial autocorrelation function)
inspection, has been tried out to obtain suitable orders of autoregressive (p) and moving average (q) parameters for the ARMA(p,q)/ARIMA(p,d,q)
models. Forecasting performance of the selected ARMA(p,q)/ARIMA(p,d,q) models has been evaluated on the basis of MAPE (mean
absolute percentage error), MAE (mean absolute error) and RMSE (root mean square error) indicators. For 20 out of sample forecasts,
one step (i.e., one day) ahead MAPE for CO, NO2, NO and O3, have been found to be 13.6, 12.1, 21.8 and 24.1%, respectively. Given the stochastic nature of air pollutants data and in
the light of earlier reported studies regarding air pollutants forecasts, the forecasting performance of the present approach
is satisfactory and the suggested forecasting procedure can be effectively utilized for short term air quality forewarning
purposes. 相似文献
10.