NOPR Collection:

An opto-microwave phase-locked receiver for SCM signals*

2014-01-21T16:33:44Z

Title: An opto-microwave phase-locked receiver for SCM signals* Authors: Biswas, B N; Pal, S; Bhattacharya, A; Mondal, D; Lahiri, P Abstract: A broadband receiver for the recovery of the subcarriers of coherent subcarrier multiplexing (SCM) signals has been presented. Unlike its predecessors this receiver generates negligible inter-modulation noise, and is capable of reducing the effect of laser phase noise to a large extent. Numerical experiments agree well with the theoretical findings. Page(s): 53-58

Spectral characteristics of surface fields in the Indian seas and inter-annual monsoon variability

2014-01-21T16:33:29Z

Title: Spectral characteristics of surface fields in the Indian seas and inter-annual monsoon variability Authors: Mohanty, Pratap K; Dash, Sushil K Abstract: Spectral analysis and variance have been employed on sea surface temperature (SST), mean sea level pressure, zonal and meridional wind stress, latent and sensible heat fluxes of four regional domains in the Indian Ocean. The data for the present study consist of the uninitialized European Center for Medium Range Weather Forecasts (ECMWF) model analyses (00 UTC) from 1985 to 1990. Composite time series and power spectra do not depict well the contrast between below normal and normal/above normal monsoons. But the composite variance spectra reflect the contrasting features very well. Differences in coherence and phase propagation of surface fields, especially in the seasonal band, between normal/above normal and below normal monsoon years are apparent from the cross-spectrum analysis and these indicate the significant role of phase propagation in the seasonal and inter-annual monsoon variability. Page(s): 43-52

Estimation of absorption and electrical path length at 22.235 GHz

2014-01-30T16:33:37Z

Title: Estimation of absorption and electrical path length at 22.235 GHz Authors: Karmakar, P K; Rahaman, M; Chattopadhyay, S; Sen, A K; Gibbins, C J Abstract: Radiometric studies at the weak water-vapour-resonant frequency centered at 22.235 GHz have been made during clear sky conditions. Data obtained in presence of rain and cloud cover have been intentionally discarded. Monthly variations of absorption in clear weather have been compared with those obtained by using radiosonde data. The results reveal that the absorption is maximum during the months of July through August. A difference was found to exist between the measured values of atmospheric noise temperature and those obtained by calculation, which is discussed in terms of mean medium temperature and ground temperature. The monthly variation in the excess wet-path length at 22.235 GHz, determined from the measurements of brightness temperature, is also considered. Comparison have been made between the calculated and measured values of this excess electrical path length. The maximum excess path length experienced by the microwave signal is about 40 cm, occurring in the monsoon season. This is due to the high abundance of water vapour during the monsoon season over Calcutta. The minimum path length deduced was 15 cm in the non-monsoon season. Page(s): 36-42

An ion-aerosol model study for the stratospheric conductivity under enhanced aerosol condition

2014-01-20T16:33:07Z

Title: An ion-aerosol model study for the stratospheric conductivity under enhanced aerosol condition Authors: Srinivas, N; Prasad, B S N; Nagaraja, K Abstract: An ion-aerosol model study of the stratospheric ion conductivity is made for an enhanced aerosol condition of the region. For analyzing the effect of aerosols on conductivity, the aerosol number density alone is not sufficient. From this study it is found that the aerosol ion-small ion recombination coefficient (α_s) determines the extent to which aerosols can reduce the conductivity of the stratosphere. This necessitates the requirement of experimental measurements of α_s along with simultaneously measured aerosol density and conductivity in the region. Page(s): 31-35