The rain-induced depolarization of a Ku-band satellite signal has been studied at a tropical location, Kolkata (22°34'N, 88°29'E). The depolarization phenomenon is observed in terms of an enhancement of cross-polar component of a horizontally polarized Ku-band satellite signal at the present location. The differential phase shifts, dominantly responsible for causing depolarization caused by scattering of oblate spheroidal rain drops at Ku-band, are computed by employing the point matching technique and utilizing rain drop size distribution data, experimentally obtained at the present location. The differential phase shift is significant for large rain drops resulting in greater depolarization of signal. Consequently, rain drop size distribution plays an important role in determining the depolarization of the satellite signal. The relationship of cross-polar enhancement with rain rate shows a seasonal variation indicating higher extent of depolarization during the pre-monsoon period than during the monsoon period, the reason being the dominance of larger rain drops in the pre-monsoon period compared to the monsoon months for identical rain rates. © 2014 Elsevier Ltd.

A MAITRA

A ADHIKARI

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Journal of Atmospheric and Solar-Terrestrial Physics

This paper studies the rain-induced propagation characteristics over a tropical location Kolkata, India, using the data collected over a 7 year period, i.e., 2004-2010. This location experiences substantial rainfall during the Indian Summer Monsoon (ISM) season which is preceded by premonsoon rainfall accompanied by strong convection. Accumulations, event duration, and fade duration statistics are presented. Long-term observations for three propagation effects, namely rain attenuation, scintillations, and depolarization, are analyzed in this paper. The seasonal patterns of these phenomena are examined to reveal the characteristic features of Kolkata. The interrelations among rain rate, rain attenuation, scintillations, and depolarization are also investigated. Propagation detriments for identical rain rates are more severe in premonsoon compared to monsoon period, mainly because of the different microphysical properties of precipitation. However, the percentage occurrences of various propagation effects are higher in monsoon than premonsoon. © 1963-2012 IEEE.

IEEE Transactions on Antennas and Propagation

Rain and rain-induced degradations of satellite links over a tropical location

Efficient use of satellite communication in tropical regions demands proper characterization of rain attenuation, particularly, in view of the available popular propagation models which are mostly based on temperate climatic data. Thus rain attenuations at frequencies 22.234, 23.834 and 31.4/30 GHz over two tropical locations Kolkata (22.57°N, 88.36°E, India) and Belem (1.45°S, 48.49° W, Brazil), have been estimated for the year 2010 and 2011, respectively. The estimation has been done utilizing ground-based disdrometer observations and radiometric measurements over Earth-space path. The results show that rain attenuation estimations from radiometric data are reliable only at low rain rates (<30 mm/h). However, the rain attenuation estimations from disdrometer measurements show good agreement with the ITU-R model, even at high rain rates (upto100 mm/h). Despite having significant variability in terms of drop size distribution (DSD), the attenuation values calculated from DSD data (disdrometer measurements) at Kolkata and Belem differ a little for the rain rates below 30 mm/h. However, the attenuation values, obtained from radiometric measurements at the two places, show significant deviations ranging from 0.54 dB to 3.2 dB up to a rain rate of 30 mm/h, on account of different rain heights, mean atmospheric temperatures and climatology of the two locations. © 2018 Elsevier Ltd

Rain attenuation studies from radiometric and rain DSD measurements at two tropical locations

Propagation effects on Ku-band over an earth-space path is carried out at Kolkata, India, a tropical location, by receiving a Ku-band signal with horizontal plane polarization transmitted from the geostationary satellite NSS-6 (at 95°E). The amplitude of co-polar attenuation has been monitored along with the measurements of rain rate, rain drop size distribution and height profile of rain rate. The cross-polar enhancement of the signal is also monitored by receiving the same signal in orthogonal direction with another identical receiver. The experimental observations are used to study the effect of melting layer on both co-polar attenuation and cross-polar enhancement for the rain events observed during 2012-2013. Melting layer is indicated by the bright band signature in vertical profile of rain rate. The ground based drop size measurements indicate that the stratiform rain has more number of small drops whereas convective rain composed of large rain drops. The results indicate that the depolarization due to melting layer is more dominant compared to that due to the drop deformation mechanism at low rain rates. © 2014 Elsevier Ltd.

Effects of melting layer on Ku-band signal depolarization

A severe cyclone, named Aila, passed over Kolkata on 25 May 2009. The strong convective activities manifested through rainfall during the cyclone were studied with multi-technique observations involving micro rain radar, disdrometer, rain gauges, and a Ku-band satellite signal receiving system. A number of features of precipitation, namely the presence of large rain drops, the large vertical extent of the precipitating layer, an unusual enhancement of cross-polar component, and strong scintillations of the co-polar component of the satellite signal due to strong turbulences associated with the cyclone, were observed. This study leads to a more comprehensive understanding of the precipitation associated with a cyclonic storm. © 2013 Copyright Taylor and Francis Group, LLC.

International Journal of Remote Sensing

Multi-technique observations on precipitation and other related phenomena during cyclone Aila at a tropical location

The phenomenon of scintillations in relation to rain attenuation of Ku-band satellite signals has been studied at a tropical location. The standard deviation σ of scintillations increases with attenuation up to a value in the range of 6-7 dB, beyond which σ decreases with attenuation. A technique is proposed to obtain some effective values of structure constant C n 2 of refractive-index variation from the experimental observations of σ and rain rate (R). The value of C n 2 also increases with attenuation up to values in the 6-7-dB range and decreases beyond that value. The eddies in turbulent raining medium grow with rain rate, and consequently with attenuation, causing an increase in the outer scale (L O) of turbulence and thus increasing σ until L O reaches the size of the first Fresnel zone. In a further development, the contribution of L O toward C n 2 decreases, resulting in the decrease of fast fluctuations with rain attenuation. © 2012 IEEE.

IEEE Geoscience and Remote Sensing Letters

Rain-induced scintillations and attenuation of ku-band satellite signals at a tropical location

An attempt has been made to inter-relate simultaneously occurring rain attenuation and scintillations of Ku-band signals over an Earth-space path at a tropical location. The power spectral analysis has been carried out to determine required cut-off frequency of filtering to separate out rain attenuation and scintillation effects. The power spectra of low- and high-pass filtered time series of satellite signal level data exhibit respective slopes in frequency domain that support theoretical values. Furthermore, wavelet analysis reveals the variability of different modes of signal variations in time-frequency space and the two phenomena are related by means of their global wavelet spectra. © 2010 Elsevier Ltd.

Studies on the inter-relation of Ku-band scintillations and rain attenuation over an Earth-space path on the basis of their static and dynamic spectral analysis

Rain attenuation is an important aspect of signal propagation above 10 GHz frequency. The attenuation time series generation from point rain rate measurement is crucial due to unavailability of actual signal measurements. In this paper, a simple and realistic approach has been demonstrated for better estimation of rain attenuation using Ku-band signal propagation data and ground rain rate measurements at Kolkata, India. The ITU-R model of rain attenuation has been modified by incorporating an effective slant path model. The effective slant path has been estimated and modelled in terms of a power-law relationship of rain rate data of 2007-2008. The methodology has been validated with the measured data of 2006. Comparison with ITU-R and SAM clearly demonstrates the improved predictability of the proposed model at the present tropical location.

Journal	Data powered by TypesetJournal of Atmospheric and Solar-Terrestrial Physics
Publisher	Data powered by TypesetElsevier Ltd
ISSN	1364-6826