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Indian Journal of Radio & Space Physics (IJRSP)

Title: Large scale anomalous temperature and wind variations in the lower and middle atmospheres during the solar eclipse of 15 January 2010

Authors: Ramkumar, T K; Ghosh, Priyanka; Reddy, K Krishna; Kumar, K Niranjan; Kumar, S Balaji; Reddy, A Hari Krishna; Reddy, M Venkatrami; Prasad, S B Surendra

Abstract: During 12-17 January 2010 centered around 15
January, annular solar eclipse event occurred over the Indian tropical region.
The Indian Space Research Organisation (ISRO) sponsored and provided 18 GPS
radiosondes (ISRO developed Dr Pisharoty sondes) to the Department of Physics, Yogi Vemana
University, Kadapa
(14.5°N, 78.9°E), to study the effects of solar eclipse on the atmospheric
dynamics and structure. The analyses of the data obtained from these
radiosondes launched by balloons indicate that during this eclipse period, the
atmosphere experienced ever recorded largest stratospheric cooling (maximum
cooling of ~15 K at 36 km). As a first time ever report, significant localized
variations in the strength of the large-scale zonal Walker and meridional Hadley circulations
were also found over the Indian longitude region during this solar eclipse

Page(s): 75-82 2014/03/04 - 12:57

Title: A case study of gravity waves observed in OH rotational temperatures at Kolhapur (16.8ºN, 74.1ºE), India

Authors: Parihar, Navin; Mukherjee, G K

Abstract: Ground-based
measurements of OH (8, 3) Meinel band emissions were carried out at Kolhapur (16.8ºN, 74.1ºE), India during November 2002 – May
2003 using two tilting filter photometers. OH rotational temperature ~ a proxy
of atmospheric temperature around 87 km, were derived from the intensity
information of P1(2) and P1(4) lines of OH (8, 3) band.
On most nights, strong well-defined oscillations having periodicities in the
range of 1 – 3 h were observed in OH temperature series. In this paper, a case
study of such short-period oscillations, observed on few nights in the OH
temperature, has been presented.

Page(s): 67-74 2014/03/04 - 12:57

Title: Modulation of thermal structure in the upper troposphere and lower stratosphere (UTLS) region by inertia gravity waves: A case study inferred from simultaneous MST radar and GPS sonde observations

Authors: Das, Siddarth Shankar; Kumar, K K; Uma, K N; Ratnam, M V; Patra, A K; Das, S K; Ghosh, A K; Jain, A R

Abstract: The observations of multiple layer
structures in the MST radar backscattering echoes in the upper troposphere and
lower stratosphere (UTLS) region are discussed in this paper. The fact remains
same that the enhanced echoes seen in the radar backscattering are due to the
strong positive and negative thermal gradients. Simultaneous observations of
MST radar
(1 hourly) and GPS sonde (6 hourly) over a tropical station Gadanki (13.5°N,
79.2°E) reveal the presence of 1.5-2 km vertical wavelength in the winds,
temperature and radar backscattering echoes in the UTLS region during Indian
summer monsoon (ISM). The analysis also reveals that the presence of inertia gravity
wave (IGW) triggered due to tropical easterly jet (TEJ) associated with ISM is
the prime candidate for the observed thermal gradients in the UTLS region.

Page(s): 11-23 2014/03/04 - 12:57

Title: Effect of cumulus and microphysical parameterizations on the JAL cyclone prediction

Authors: Reddy, M Venkatarami; Prasad, S B Surendra; Krishna, U V Murali; Reddy, K Krishna

Abstract: Weather
Research and Forecasting (WRF) model is used to predict the track and intensity
of JAL cyclone, which formed during 04-08 November 2010 over the Bay of Bengal.
The model has been simulated with numerous experiments using the logical/scientific
combination of convection and micro-physics schemes. The model simulations have
been conducted
with different initial conditions to know the effective track and intensity
prediction of JAL cyclone. In
addition, the effect of cumulus
parameterization schemes at different resolution (27 and 9 km) on the cyclone
track and intensity is reported.
The model simulated results showed the importance of cumulus schemes and their
role at 9 km horizontal resolution.
The results indicate that the track predicted by
Kain-Fritsch (KF) scheme is in
good agreement with the observed track in all the experiments and the land fall
error is minimum (~11 km) for the combination of Ferrier and KF scheme with 0000 hrs UTC on 04 November 2010
as initial condition. Strong intensity
is produced by KF, New Grell (NG) schemes and weak intensity is produced by Betts-Miller-Janjic (BMJ) scheme
with all microphysics parameterization (MP) combinations. Further, the dependency of intensity of cyclone has been studied in
terms of surface latent heat flux, divergence and vorticity fields. To validate the model performance, different
meteorological parameters are derived from the model simulations over three
different regions and are compared with the observed meteorological parameters.
The model results are in good agreement with the observed parameters, but
variations are observed at the landfall /dissipation of the cyclone.

Page(s): 103-123 2014/03/04 - 12:57

Title: Preliminary results on equatorial spread-F irregularities by VHF and HF radars

Authors: Sekar, R; Kherani, E A; Viswanathan, K S; Patra, A K; Rao, P B; Devasia, C V; Subbarao, K S V; Tiwari, D; Ramachandran, N

Abstract: Preliminary
results obtained from a co-ordinated campaign involving simultaneous operation
of VHF (53 MHz) and HF (18 MHz) radars, located at Gadanki and Trivandrum, on
the structures and dynamics of equatorial spread-F irregularities are reported.
Such kind of measurement involving 18 MHz radar is attempted, probably, for the
first time. The

structures as
revealed by both VHF and HF radars are more or less similar. However, the
Doppler velocities transverse to earth's magnetic field of the 3m
irregularities as observed by VHF radar reveal a maximum velocity of 200 ms-1
in the central regions of plume structures, while the corresponding velocities
of 8.3 m irregularities observed by HF radar reveal a

maximum of
around 50 ms-1 in contrast to the earlier expectations. This
suggests significant dispersive nature indicating that different physical
processes are operational in these wavelength regime. Further the observations
by VHF radar revealed the plume structures which are generally found to be
vertically erect in the altitude region of 300-450 km without having much tilt
indicating that the shears in the zonal plasma drift are not significant in
this altitude region during equinoctial period over Indian longitude.

Page(s): 262-271 2014/01/22 - 21:01

Title: Detection of pre-sunrise echoes at mesospheric heights

Authors: Ratnam, M Venkat; Rao, T Narayana; Rao, S Vijaya Bhaskara; Rao, D Narayana; Kumar, Y Bhavani; Raghunath, K

Abstract: Indian MST radar
located at Gadanki has been operated in special mode during equinox, i.e. on 23
and 24 Mar.1999 for detection of pre-sunrise echoes at mesospheric heights.
These echoes are observed on both the days, 30 to 60 min before sunrise at
ground level. On the first day, the radar is operated only in vertical
direction and found that the echoes are highly intermittent in space and time
similar to the daytime echoes. These echoes are observed mainly above 85 km
with a peak at 90 km height on both the days. Echoes are also observed below
these heights but less frequently. The Doppler shift and Doppler width on 23
Mar. 1999 is found to be of the order of +2 Hz and 4 ms-1,
respectively. On 24 Mar. 1999, radar was operated by using three different
beams (east, zenith Y and south) in order to see whether these echoes are due
to turbulence or due to some other mechanism. Interestingly echoes in all the
beam positions are observed indicating that the echoes are due to turbulence.

Page(s): 258-261 2014/01/22 - 21:01

Title: Middle atmospheric temperature measurements using a ground based lidar from low latitude

Authors: Kumar, Y Bhavani; Kumar, V Siva; Rao, P B; Krishnaiah, M; Mizutani, Kohei; Aoki, Tetsuo; Yasui, Motoaki; Itabe, Toshikazu

Abstract: Lidar
measurements of atmospheric density and temperature in the altitude range 30-80

have been
performed during the period March-December 1998, using NMRF-IJL, Gadanki
(l3.8°N, 79.2°E). Sample results on temperature structures in the periods of
equinoctial, summer and winter nights, results on wave propagation and evidence
of mesospheric

inversion on an occasion are presented. The data analysis, method of
temperature determination and its standard error are also described.

Page(s): 249-257 2014/01/22 - 21:01

Title: Thin aerosol clouds at tropopause level

Authors: Murthy, B V Krishna; Nayar, S R Prabhakaran; Revathy, K; Satheesan, K; Parameswaran, K; Nair, Prabha R; Murthy, K Krishna; Rao, P B; Bhavanikumar, Y; Raghunath, K; Sivakumar, V; Krishniah, M

Abstract: Aerosol clouds
about 2 km below the tropopause are studied using the data from lidar and MST
radar at Gadanki. The cloud shows fluctuations with time scales as short as 1/2 h in
the backscatter ratio. Depolarization factor indicates ice crystal formation
when the cloud is strong. The MST radar wind data show strong turbulence below
the cloud level indicating,

turbulent mixing /transport of water vapour from lower heights to cloud heights
facilitating cloud formation.

Page(s): 245-248 2014/01/22 - 21:01

Title: Retrieval of water vapour profiles from radio occultation refractivity using artificial neural network

Authors: Shyam, Abhineet; Gohil, B S; Basu, Sujit

Abstract: Artificial neural network (ANN) technique
has been used to derive water vapour pressure profiles in the troposphere from
radio occultation data over India and adjoining region. A fully connected
three-layer network, with one hidden layer, has been constructed and standard
back propagation algorithm has been used to train the network. While month, latitude
and vertical profile of refractivity/bending angle constitute the input vector, the
water vapour partial pressure profile forms the output vector. Only the moisture-laden summer
monsoon months of June, July, August and September of 2010 have been considered
for developing the retrieval algorithm. There are 2120 input and output pairs,
out of which 1696 pairs form the training set while the remaining pairs
constitute the validation set. The retrieved profiles of water vapour pressures
in the validation set have been compared with the corresponding COSMIC
operational products of water vapour pressure profiles. The effectiveness of
the algorithm is apparent from this comparison and also from the vertical
profiles of bias and root mean square error (RMSE). The statistics show
better performance of the algorithm with refractivity as one of the inputs than
with bending angle. The RMSE in water vapour retrieval from refractivity is
within 1.5-2 hPa compared to markedly higher values of 6 hPa when derived from
bending angle. Additionally, the algorithm has also been
tested in an independent year 2009 and the performance of the refractivity
based retrieval has been found to be highly consistent in the year 2010, with RMSE
within 1.5 hPa.

Page(s): 411-419 2013/12/27 - 10:22

Title: Assessment of electromagnetic radiation for second and third generation frequency spectrum on human body

Authors: Sharma, Pragati; Gautam, A K; Kumar, Sandeep

Abstract: The rapid
diffusion of wireless communication systems such as mobile phones has caused an
increased concern for the potential effects on human health deriving from
exposure to electromagnetic fields emitted by antennas and base stations of
these systems. A number of studies have been conducted on the topic of
electromagnetic field effects over human body. All earlier studies were
centered on the second generation (2G) global system for mobile communication
(GSM). Now, third generation (3G) mobiles and towers have been launched in the
market, therefore, it is high time to calculate the radiation effect of increased
frequency of 3G system over human body. In this paper, the specific absorption
rate (SAR) value for skin (dry and wet) tissues of human body have been
evaluated at 900, 1800 and 2140 MHz frequency bands. The first two frequencies
represent the second generation (2G) and the third frequency represents the
third generation (3G), respectively. The skin exposure due to base transceiver
station (BTS) is calculated through SAR up to a distance of 3.5 mm inside skin
for these frequencies. It has been found that values of SAR for electromagnetic
radiation due to 2G and 3G frequency spectrums are very highly distributed near
the source of radiation (BTS) and SAR have more effect on skin as one moves
towards higher frequency band.

Page(s): 425-428 2013/12/27 - 10:22

Title: Comparison of SMOS soil moisture/brightness temperatures for morning and evening passes

Authors: Calla, O P N; Sharma, Rahul; Gadri, Kishan Lal; Kalla, Abhishek; Agrahari, Sunil Kumar; Rathore, Gaurav

Abstract: Soil moisture is an essential element, which
controls the land-atmospheric system and thus, its continuous monitoring is
extremely important. Regular monitoring of spatio-temporal variability of
surface soil moisture can be done using microwave remote sensing techniques, as
there is high contrast in dielectric properties of pure dry soil (2-3) and pure
water (80) at microwave frequencies. Variation in surface soil moisture is not
only affected by precipitation, evaporation and transpiration, but often
groundwater and root zone moisture also play an important role. In the present
paper, surface soil moisture data from Soil Moisture and Ocean Salinity (SMOS)
satellite is used to analyse the changes in surface soil moisture from evening
to next or following morning (6.00 PM and 6.00 AM) in an arid region of
Rajasthan, India. An increase in surface soil moisture is observed for maximum
data from evening to following morning. The same trends were also verified
using polarization index values.

Page(s): 420-424 2013/12/27 - 10:22

Title: Effects of backscattering enhancement considering multiple scattering in rain on MMW radar performance

Authors: Yang, Rui-Ke; Li, Li; Ma, Hui-Hui

Abstract: The theory of the
second order backscattering enhancement in discrete random medium is discussed
in this paper.
The effects of rainfall on millimeter wave (MMW) radar performance are analysed
based on Mie theory, Monte Carlo (MC) simulation and backscattering enhancement
theory, at 35 and 95 GHz, respectively. The rain attenuation considering the
raindrops multiple scattering is introduced into the estimation of the signal
to clutter ratios (S/C) and the clutter to noise ratios (C/N) for MMW radar. The
S/C and C/N are calculated by means of the backscattering enhancement, Mie
theory and MC simulation method, respectively under the condition of rain
environment. The results show that the S/C obtained by backscattering
enhancement theory is smaller than the results by Mie and MC. The C/N by
backscattering enhancement is greater than the results by other. The Mie and MC
methods do not consider backscatter enhancement, underestimate the effect of
raindrops scattering on radar performance. Hence, it is shown that the
attenuation and backscattering enhancement induced by raindrops multiple
scattering are necessarily taken into account for the performance estimation of
MMW radar operating in
heavy rainfall environment.

Page(s): 404-410 2013/12/27 - 10:22

Title: COSMIC Satellite observations on seasonal variation of pressure at cold point tropopause and its relation with tropical easterly jet over tropical region

Authors: Kumar, V; Dhaka, S K; Jain, A; Chaudhary, A; Bhatnagar, R; Gupta, A; Panwar, V; Singh, N; Reddy, K K

Abstract: 92.60.hf;
92.60.hv; 93.30.Vs; 84.40.Ua

Page(s): 292-297 2013/11/06 - 10:34

Title: Hourly radiosonde observation of humidity and temperature and high resolution vertical wind using the Equatorial Atmosphere Radar during convection over Koto Tabang, Indonesia in CPEA-II campaign

Authors: Bhatnagar, R; Panwar, V; Shibagaki, Y; Hashiguchi, H; Fukao, S; Kozu, T; Takahashi, M; Dhaka, S K

Abstract: Distinct wave
perturbations for ~ 2-3 hours were observed during Coupling Processes in
Equatorial Atmosphere-II in temperature and
vertical wind in the tropopause region (~17-19 km) using hourly radiosonde
launchings and high resolution Equatorial Atmosphere Radar observations,
respectively over Koto Tabang (100.32°E, 0.20°S) during active convective
events. Perturbations in temperature and humidity were found to be strongly
anti-correlated in the upper troposphere and lower stratosphere region.
Observations suggest that convective storm had increased humidity by a factor
of 3-5 in the middle and upper troposphere (water vapour mixing ratio were also
increased over convective period); gravity waves were generated near and above
tropopause, which were not detected during no-convection period. Hourly
temperature observations, which have covered complete life cycle of two convective
storms of 7-8 hours, showed a significant enhancement in water vapour mixing
ratio up to ~15-16 km height that corresponds to a level of strong wind shear
existing below tropopause. There is a significant decrease in temperature
around this level of strong wind shear.

Page(s): 277-291 2013/11/06 - 10:34

Title: Airglow measurements of wave damping at upper mesospheric altitudes over a low latitude station in India

Authors: Taori, A; Kamalakar, V

Abstract: In
this paper, nighttime mesospheric OH and O2 temperature variability
over Gadanki, a low latitude station in the Indian sector during February 2010
have been studied. It has been noted that mesospheric wave amplitudes show
large variability from one night to the other. Occasionally, the mesospheric
waves show larger amplitudes in O2 data compared to the amplitudes
of similar period waves in OH data indicating the amplification in wave
amplitudes. For the waves noted simultaneously at OH and O2 data,
the damping factors have been calculated. The analysis reveals a highly dynamic
upper mesosphere with some of the waves showing upward propagation (damping
factor < 1), some reaching to their saturation levels (damping factor ~1)
and few waves getting strongly damped (damping factor >1).

Page(s): 371-379 2013/11/06 - 10:34

Title: VHF radar observations of mesospheric echoes and their relationship with thermal structure over Gadanki (13.5°N, 79.2°E)

Authors: Sridharan, S; Suresh, M; Ramesh, K

Abstract: There have been several reports on the
comparison of daytime mesospheric echoes and their relationship with nighttime
thermal structure. In the present work, a few cases are presented in which
mesospheric echoes, observed with the MST radar at Gadanki (13.5°N, 79.2°E)
during January-February 2011, are compared with temperature information
obtained by Sounding of Atmosphere by Broadband Emission Radiometry (SABER)
instrument onboard Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics
(TIMED) satellite, when there is an overpass near Gadanki close to the time
when the echoes are observed. It is found that the mesospheric echoes occur at
heights where temperature is minimum or tends to be minimum as compared to the
temperature at adjacent heights. The temperature lapse rate decreases below and
increases above the height of maximum echoes. This relationship is consistently
observed in all the cases considered in the present work. It appears that
echoes arise due to change in the refractive index associated with electron
density fluctuations caused probably by wave breaking and subsequent
turbulence, which could be inferred from the minimum temperature (dynamical
cooling) at the height of wave breaking.

Page(s): 364-370 2013/11/06 - 10:34

Title: Phase only pattern synthesis for antenna array using genetic algorithm for radar application

Authors: Kumar, Pramod; Singh, A K

Abstract: The present
paper describes the phase only pattern synthesis for the active phased array
antenna using genetic algorithm. The phase only synthesis is required to
broaden and shape the beam in transmit mode of operation where all elements are
fed through the saturated power of transmit/receive modules (TRM). This
technique is very useful in multifunctional radar application where broadened
beam can occupy more search volume (reduction in frame time). The real coded
genetic algorithm (GA), which has ability to find solution of complex problems,
has been exploited to get the required shaping of the beam. GA based software
is a high performance optimizer and is very easy to understand and implement.

Page(s): 259-264 2013/09/09 - 22:05

Title: Analysis of vertical drifts in the post sunset equatorial F-region during geomagnetically quiet and disturbed periods

Authors: Simi, K G; Vineeth, C; Pant, T K; Alex, S

Abstract: This paper reports the HF Doppler Radar measured post
sunset F-region vertical drift (Vd) over Trivandrum
(8.5°N, 77°E, 0.5°N dip latitude) during quiet and disturbed periods. In
general, Vd showed significant day-to-day variability, both in the
overall trend and the nature of short period oscillations present. Analysis
based on the simultaneous measurements of equatorial electrojet (EEJ) induced
surface magnetic field (ΔH) and interplanetary magnetic field (IMF) revealed
that the Vd, on geomagnetically quiet days, exhibit oscillations of
periodicity 15-20 minutes; whereas on disturbed days, it exhibit a dominant
oscillation of ~ 45 minutes periodicity, similar to the one present in the IMF.
Overall, the vertical drifts during quiet days seemed to be controlled by
gravity waves of lower atmospheric origin. On the other hand, during disturbed
time, the vertical drift is controlled by the interplanetary medium through the
coupled electric field. It has also been observed that whenever post sunset Vd
showed enhanced oscillation of 15-20 minutes periodicity, the equatorial
spread-F occurred.

Page(s): 229-239 2013/09/09 - 22:05

Title: Cosmic ray and geomagnetic response to radio-loud coronal mass ejections (CMEs)

Authors: Sharma, N K

Abstract: A catalog of type
II bursts observed by the Radio and Plasma waves (WAVES) experiments onboard
the wind space craft and the associated coronal mass ejections (CMEs) observed
by the Solar and Heliospheric Observatory (SOHO) mission are used to study the
influence of medium and high speed coronal mass ejections on cosmic ray neutron
intensity during 1997-2008, which corresponds to the solar activity cycle 23.
The CMEs in the catalog are called radio-loud CMEs because of their ability to
produce type II bursts. It is noteworthy that the occurrence of high speed
coronal mass ejections is significantly high during 1997-2008. The results
indicate that the magnitude of the depression in cosmic ray intensity is large
for high speed coronal mass ejections in comparison with the low and medium
speed CMEs. It is observed that in all three cases, the depression in cosmic
ray intensity is maximum on +4 day after the arrival of the CMEs. Also, the
geomagnetic perturbations are more pronounced on + 4 day after the arrival of
CMEs for low and medium speed coronal mass ejections.

Page(s): 213-218 2013/09/09 - 22:05

Title: Nighttime enhancement of ionospheric parameters

Authors: Singh, Anup K; Sardar, Nuzhat; Rizvi, Sahla; Rathore, Sanjay; Vijay, S K

Abstract: In the present work, ionospheric electron
content (IEC) as well as critical frequency of F2 layer (foF2) data from three
locations (low, mid and high latitudes) have been used to study the anomalous
nighttime F-region during low to moderate solar activity period, i.e. from
January 2006 to December 2010. The results show that at high and mid-latitude
locations, there is maximum percentage of enhancement in IEC and foF2 during
winter season, whereas at low latitude location, maximum percentage of
enhancement in both the parameters is during equinox. The highest total number
of enhancements in IEC parameter occurred at high latitude station Chilton,
whereas in foF2 parameter, highest total number of enhancements occurred at low
latitude station Kwajelin. Out of 1116 enhancements in IEC, 661 enhancements
occurred during pre-midnight hours and 455 during post-midnight hours. Although
out of 948 enhancements for foF2, 457 enhancements occurred during pre-midnight
hours and 491 during post-midnight hours.

Page(s): 240-250 2013/09/09 - 22:05

Title: Troposphere induced GPS navigation error, its effect on GPS-INS integrated system performance and mitigation strategies

Authors: Harikumar, G; Karthikeyan, K; Syamala, S; Pillai, C Radhakrishna; Hemachandran, S; Shukkoor, A Abdul; Mohanlal, P P

Abstract: Conventional
Global Positioning System (GPS) receivers track GPS satellites above 5 degree
horizon to avoid multipath effects. In order to improve vertical dilution of
precision (VDOP), it is an attractive prospect to utilize GPS satellites below
the horizon in addition to those above, for navigation computations in GPS
receivers used by vehicles operating at high altitude trajectories. This paper,
however, exposes a possible risk of navigation output degradation in adopting
this scheme due to unintentional occultation of GPS signals from satellites
below the earth tangent horizon. The error on GPS range and range
rate measurements induced by troposphere are simulated using a model based
approach. Results indicate position errors up to 150 m and velocity errors up
to 14 ms-1 over a period of 15 s under practical conditions. Such
slowly varying errors being uncharacteristic of GPS receivers are not rejected
by the usual protection features in GPS-Inertial Navigation System (INS)
integration schemes. Thereby, the integrated system performance is degraded. In
the uncoupled GPS-INS scheme studied, GPS error of the above order resulted in
integrated system output error of 100 m in position and 5 ms-1 in
velocity, respectively.
An altitude based elevation cut off scheme that can be incorporated in the GPS
receiver for retaining the advantages of using negative elevation satellites,
while avoiding occulted measurements, is presented in this paper. A method for
strengthening integrated scheme protection, using innovation residuals, for
rejecting such slow GPS errors is also presented.

Page(s): 150-158 2013/07/11 - 21:07

Title: Pratham satellite: Faraday rotation based TEC measurement

Authors: Prashanth, Giri; Kumar, Avnish; Mulay, Sanyam

Abstract: Pratham, the student satellite of Indian
Institute of Technology Bombay is a landmark project undertaken by the students
of the institute in collaboration with ISRO. The project is in its environment
testing phase now. Total electron content (TEC) measurement was chosen as the
payload for the satellite keeping in mind the current scientific atmosphere in
India with the Indian Regional Navigational Satellite System (IRNSS) and GPS-Aided
Geo-Aumented Navigation (GAGAN) system in the process of development. This
paper describes the use of Faraday rotation method for TEC measurements.
The key features of the method, n-pi ambiguity resolution, possible sources of
error and simulations carried out to get
the initial estimates of the TEC values are also discussed. The on-board and
on-ground hardware implementation are
briefly explained.

Page(s): 197-203 2013/07/11 - 21:07

Title: GPS signal Rician fading model for precise navigation in urban environment

Authors: Rao, G Sasi Bhushana; Kumar, G Sateesh; Kumar, M N V S S

Abstract: Global Positioning System (GPS) usage is not
limited to the aircraft en-route navigation and missile guidance where the user
receives the satellite signals from the open sky. Currently, GPS has become an
essential utility in the car navigation, mobile phones, surveying and aircraft
landing applications. The received signal strength of a GPS satellite at a
given location on or near the earth surface can be predicted by analyzing the
propagation characteristics of the channel with an appropriate propagation
model. The signal propagation characteristics particularly the short term
variations severely affect the quality, availability and continuity of the
system. The short term propagation characteristics of GPS signal is modeled and
analyzed in this paper. Short term variations are mainly due to multipath
reflections and Doppler shift which degrades the quality of received signal
particularly in urban environments. The variation of signal quality with respect
to user velocity is observed using Rician fading model.

Page(s): 192-196 2013/07/11 - 21:07

Title: An optimal method for parameter retrieval from Radio Occultation Missions

Authors: Rajarajan, D; Babu, R; Saha, Shibu; Rathnakara, S C

Abstract: Radio occultation (RO) is the Global
Navigation Satellite System (GNSS) based remote sensing of Earth’s atmosphere
for atmospheric parameter retrieval and total electron content (TEC)
computation. Several RO missions have been launched by ISRO, viz.
Meghatropiques and Oceansat-2, for atmospheric studies. Current implemented
methods are able to provide the parameters only in post processed mode and
hence, are available after some duration. This is due to the limitation of
availability of precise satellite orbit for GNSS and LEO satellites which
serves as one of the fundamental input to the process. However, a faster
turnaround time is possible if the parameters are computed in near real time
from the on-board solutions. This paper highlights the work that has resulted
in optimizing the atmospheric parameter retrieval and
TEC computation using the radio occultation technique.

Page(s): 187-191 2013/07/11 - 21:07

Title: Vertical profile variations of NO2 and O3 using slant column density observations during twilight period

Authors: Londhe, A L; Bhosale, C S; Meena, G S; Jadhav, D B; Gil, M; Puentedura, O; Yela, M

Abstract: An algorithm developed to derive the
vertical profiles of atmospheric species from their slant column density measurements
using twilight spectroscopy is discussed. The algorithm has been tested by
using the slant column density measurements at polar station, Reykjavik (64°N, 22.6°W)
and tropical station, Pune (l8.53°N, 73.85°E). The vertical profiles of NO2
and O3 are retrieved by considering slant column densities for ten different
solar zenith angles and ten different atmospheric layers of equal thickness. These
vertical profiles are

used to differentiate the tropospheric and
stratospheric contribution of NO2 and O3 . The
observations of  NO2 at polar station
and at tropical station showed frequent higher values of tropospheric concentrations
due to pollution episodes and are not correlated with stratospheric NO2
and O3. The correlation between total column density variations of NO2
and O3 is not observed; however, the stratospheric variations of NO2
and O3 showed good correlation.

Page(s): 291-301 2013/05/02 - 21:09

Title: Determination of photolysis frequency of O1D in the tropical region

Authors: Paul, R; Mitra, A P; Mandal, T K; Srivastava, S K

Abstract: An attempt has been made to estimate the photolysis
frequency of O1D in troposphere and stratosphere of the Indian region.
The radiation code Lowtran 7 is used to estimate actinic flux at these altitudes.
An accurate and efficient multiple scattering parametrization along with k-distribution
method has been used in this model. For ozone, observed averaged profile for the
year 1976 as well as 1994 is used for Delhi,
Pune and Thiruvananthapuram. Values as recommended by DeMore et al. [JPL Publication,
1994, p.94] and Michelsen et al. [Geophys Res Lett (USA). 21
(1994) 2227.] have been taken for ozone quantum yield. The values of photolysis
frequency of O1D are found to be significantly higher for the quantum
yield given by Michelsen et al. A decrease in these values is also observed
in the year 1994 as compared to that in

preceding years up to 1976.

Page(s): 286-290 2013/05/02 - 21:09

Title: Solar beam radiation estimate’s correlation for Bangladesh

Authors: Rahman, M M; Uddin, M A; Islam, M W

Abstract: An empirical
correlation has been developed which correlates the monthly average daily solar beam
radiation with the maximum possible number of bright sunshine
hours. Airmass exponential correlation is also established. The applicability
of these models in climatic conditions of Bangladesh is also
studied. Measured beam radiation and the bright sunshine hour data are
analyzed to find out the regression co-efficient of these correlations
using computer simulation programme by Gaussian elimination
technique. Applying
these correlations, solar beam radiation is computed for
different locations in

Bangladesh. Predicted
results are compared statistically with the experimental observations
considering different statistical errors. The t-statistics is also
applied to test whether or not a model is statistically significant
at a particular confidence level. On the basis of the
analysis, a model has been recommended which is found to be best suited to the
climatic conditions of Bangladesh.

Page(s): 277-285 2013/05/02 - 21:09

Title: Feasibility study of extended range atmospheric prediction through time average Lorenz attractor

Authors: Pal, Pradip K; Shah, Shivani

Abstract: Though the theoretical limit of
atmospheric predictability is only up to 1-2 weeks, temporal and spatial averages
may be predictable up to certain extent for extended range. It is not known
what should be the length of time for averaging to have certain predictability of
time average values. The time average behaviour of Lorenz attractor with and
without forcing shows that there are upper and lower limits of such length of time
for averaging, beyond which the system remains chaotic.

Page(s): 271-276 2013/05/02 - 21:09

Title: Emission and scattering behaviour of bare and vegetative soil surfaces of different moist states by microwave remote sensing

Authors: Gupta, V K; Sharma, Neeta; Jangid, R A

Abstract: Dielectric
constant (ε′) and dielectric loss (ε′′) of artificially moistened soil
of Alwar have been determined at microwave frequency 9.78 GHz and at
temperature 32.5°C using wave guide cell method. In view of the active and
passive microwave remote sensing, the horizontal-horizontal radar
backscattering coefficient () for bare and vegetative soil surface have been estimated by
Integral Equation Model (IEM) and Water Cloud Model (WCM), respectively using ε′
and ε′′ of soil and view angle as input parameters. The horizontal component of
microwave emissivity (eh) for bare soil surfaces have been
determined by emissivity model. The eh for
vegetative soil surfaces determined by radiative transfer equation using
suitable vegetation dependent parameters, like single way vegetation transmissivity and single scattering
albedo (ω) for agricultural vegetation, respectively. The present study reveals
that the  for
bare and vegetative soil surface exhibit a positive correlation with
soil moisture content (SMC).
Vegetative soil surface  is lower than that of bare soil surface for
the same values of SMC and view angle. Further, eh for bare and vegetative soil surfaces
decreases with an increase in SMC. Vegetative soil surface emissivity is higher
than that of bare surface for the same values of SMC and observation angle.
Further, backscattering coefficient and emissivity for bare and
vegetative soil surfaces decrease as the angle of observation increases due to
contribution of diminished coherent component.

Page(s): 42-51 2013/03/26 - 20:55

Title: Ionospheric electron and ion temperatures response to seismic activity

Authors: Sharma, D K; Bardhan, A; Rai, Jagdish

Abstract: A connection between earthquake and
ionosphere has been proposed in the last few decades. A number of hypotheses
have been suggested as the earthquake precursory to reduce the hazard of life
and property but could not succeed. In the present study, effort has been made
to correlate the ionospheric temperature anomalies to seismic activities. The
ionospheric electron and ion temperatures were measured with the help of
Retarding Potential Analyzer (RPA) payload aboard the Indian SROSS-C2
satellite. The data is used for the period 1995-1998 in the altitude range
430-630 km over the Indian region. The details of seismic events during this
period were downloaded from the United State Geological Survey (USGS) website.
The normal day ion and electron temperatures have been compared to the
temperatures recorded during the seismic event. It has been observed that there
is significant enhancement in the electron and ion temperatures. The electron
temperature was enhanced by 1.2 - 1.5 times compared to the average normal day
electron temperature. However, the ion temperature was 1.1 - 1.3 times over the
average normal day ion temperature. The satellite data was analysed for
corresponding seismic event duration in such way that the other possible
effects are eliminated.

Page(s): 18-26 2013/03/26 - 20:55

Title: Ionospheric TEC variations during the ascending solar activity phase at an equatorial station, Uganda

Authors: Oron, S; D’ujanga, F M; Ssenyonga, T J

Abstract: The total electron content (TEC) is a vital
and most dominant ionospheric parameter that can cause Global Positioning
System (GPS) signal delays, signal degradation and in extreme cases loss of
lock. This results into inefficient operations of ground and space based Global
Navigation Satellite System (GNSS) applications. The study of TEC variability
is, therefore, useful for GNSS users in order to minimize errors where high
levels of accuracy in measurements are required. This paper presents the
diurnal, seasonal and solar activity dependence of TEC at the GPS-SCINDA
(SCIntillation Network Decision Aid) station in Kampala, Uganda (geographic coordinates:
latitude 0.3°N, longitude 32.6°S; and geomagnetic coordinates: latitude -9.3°,
longitude 104.2°) for the years 2010 and 2011. The results obtained show that
the diurnal variability in TEC at this station has a pre-dawn minimum followed
by an early morning steady increase, an afternoon maximum and then a post
sunset gradual reduction in TEC, with the equinoctial months depicting
nighttime enhancements more prominently at around 2000 hrs UT (2300 hrs LT).
Scintillation occurrence, a consequence of TEC fluctuations, was observed from
about 1800 hrs UT (2100 hrs LT) to local midnight giving S4 index
values above 0.4, with the equinox months recording higher occurrences than
other seasons. TEC variations were also seen to exhibit solar activity dependence.
The sunspot numbers and the F10.7 solar flux exhibited a good correlation with
TEC recorded over the two years.

Page(s): 7-17 2013/03/26 - 20:55

Title: Oil spill detection using SSM/I satellite data over Bombay High location in Arabian Sea

Authors: Calla, O P N; Dadhich, Harendra Kumar; Singhal, Shruti

Abstract: Oil spill pollution is a severe environmental
problem, which persists in marine environment or in inland water across the
world. It has grown to an alarming magnitude with increased levels of oil
production and transport. Thus, it is important to study and analyze this
environmental pollution. The study and detection
of oil spills can only be accomplished by satellite microwave remote sensing
techniques. As microwaves have unique all weather penetration capability and
can be used both in day and night, it does not require illumination of target
from the sun. Two types of microwave sensors [Ulaby F T
et al. Microwave remote sensing – Active and passive, Vol 1 and 3, 1981] exist: one is
passive sensor and other active sensor. Passive microwave sensor is radiometer
that operates in the microwave region and detects microwave radiation emitted
by the earth surface in addition to passively sensing emissions coming from
objects on Earth. Active microwave sensor emits microwaves toward the earth's
surface. These microwaves are reflected back from earth's surface and return
back to the sensor. In this paper, for the detection of oil spills, data of
passive microwave sensors onboard Special Sensor Microwave/Imager (SSM/I) [Hollinger J et al. Special Sensor Microwave/Imager user’s guide,
1987, 120] satellite at 19.3 GHz frequency is used and analyzed. The analyses
shows sudden decrease of brightness temperature values in both horizontal and
vertical polarization over the oil spill area (Bombay High Area, Arabian Sea)
when compared to the brightness temperature values over oil free area in the
Arabian sea.

Page(s): 52-59 2013/03/26 - 20:55

Title: Response of the mid-latitude ionospheric F2 to the total solar eclipses of solar cycle 23

Authors: Adekoya, B J; Chukwuma, V U

Abstract: A study of the response
of the mid-latitude ionospheric F2 to the total eclipses of solar cycle 23 is
presented using five-minute resolution ionospheric foF2 data obtained from 14
mid-latitude ionosonde stations located in the path of totality of eclipse. The
changes in foF2 are analysed using D(foF2), the normalised deviation of
critical frequency F2 from the quite days reference. The D(foF2) variation of
the ionosphere in the path of totality, as recorded by the ionosonde stations
in this path, is characterized by simultaneous decrease in electron density at
elapsed time of totality. The present analysis revealed that sudden Sun
radiation removal by the Moon reduces the electron production processes in the
F2-layer. The impact of total solar eclipse is clearly evident simultaneously
with the time of maximum occultation as decrease in the electron density in all
ionospheric stations. The results, further, suggest that the maximum electron
density of F2-layer redistribution processes were observed not at the time of
totality of eclipse but shortly before and after the elapsed time (i.e. about 4
min to few hours). It is noteworthy that mainly response of electron density in
ionospheric F2 region varies with the sun intensity. Also, an increase in
maximum obscuration of eclipse causes reduction in electron density production
processes and the transport processes in the F-layer are affected due to the
presence of the westward electric field which may in turn lead to the decrease
in foF2 of ionospheric F2
region. This result obtained was reasonably in good agreement with the earlier
study of ionospheric response to total solar eclipse using different
measurement and methods.

Page(s): 594-605 2013/01/16 - 12:55

Title: An estimate of kinetic energy maxima of cyclotron-resonant electrons interacting with whistler mode waves

Authors: Ikeda, M

Abstract: Active experiments
to probe hot plasma in the magnetosphere were conducted at Siple Station,
Antarctica. The
multi-stations measurements of VLF Siple signals on the ground were also
conducted in Canada. The results from the Siple active experiments at L=5.1,
the relativistic treatments, and the results obtained from the multi-stations
measurements at L=4.1 showed almost similar results. The relativistic treatment of separatrix at L=5.1 theoretically
indicates the total energy of trapped electron, which was estimated to be 0.315
to 16 keV (at maximum of V)
by estimates of parallel resonance velocity and wave magnetic field amplitude
of 11 PT, and the effective instability depending on the weak relativistic
electrons with kinetic energy 10.9 keV in the perfect resonance condition. The kinetic
energy 10.9 keV is almost coincident with some results of Sonwalkar et al. [Properties of the magnetospheric
hot plasma distribution deduced from whistler mode wave injection at 2400 Hz:
Ground-based detection of azimuthal structure in magnetospheric hot plasmas, J Geophys Res (USA), 102 (1997) 14363].

Page(s): 579-593 2013/01/16 - 12:55

Title: Effects of geomagnetic storm on middle latitude ionospheric F2 during storm of 2-6 April 2004

Authors: Adekoya, B J; Chukwuma, V U; Bakare, N O; David, T W

Abstract: A study of the intense geomagnetic storm on
2-6 April 2004 has been carried out using ionospheric data obtained from
ionosonde station in the mid-latitude stations with emphasis on the F2 region.
Ionospheric storms represent an extreme form of space weather with important
effects on ground and space-based technological systems. These phenomena are
driven by highly variable solar and magnetospheric energy inputs to the Earth's
upper atmosphere. The mid-latitude ionospheric stations are classified into two,
depending on their geographic coordinates and ionospheric storm variation (i.e.
positive and negative phases of ionospheric storm). The low-mid latitude are
characterized with geographic latitude between 20°N< low-mid ≤ 36°N, while
high-mid latitude are >36°N. The ionospheric storms are classified as
positive storms (P-storm) or negative storms (N-storm) depending on whether
maximum electron density variation is positive or negative following the onset
of geomagnetic storms (small fluctuations of less than ±20% are neglected). The
ionospheric storm produced at low-mid latitude was observed to be negative (N)
ionospheric storm at the main phase, and also the declining phase of Dst was
simultaneously depleted. The recovery phase is more pronounced with positive
(P) ionospheric storm with noticeable effect than the initial and main phase.
The D(foF2) response of high-mid latitude was observed with positive storm in
the main phase. The initial phase responded with severe negative ionospheric
storm compared to low-mid latitude with positive ionospheric storm. During the
main phase of the geomagnetic storm, positive and negative phases of ionospheric
storm prevailed in the daytime and at night.

Page(s): 606-616 2013/01/16 - 12:55

Title: Comparison between CODG TEC and GPS based TEC observations at Koudougou station in Burkina Faso

Authors: Ouattara, Frédéric; Zoundi, Christian; Fleury, Rolland

Abstract: The paper presents the
comparison between total electron content (TEC) map given by CODG model and
Rinex TEC obtained from Koudougou GPS station, which started its operations in
December 2008. The TEC observations were carried out at Koudougou station
during 5-10 December 2008 by ionosphere single layer model (SLM). The
observation of TEC profiles showed noon bite out profile with predominance of
morning or afternoon peak and night time peak. CODG TEC profiles highlighted
dome and reverse profiles. There is no night time peak in TEC map profiles. The
comparison between GPS based TEC observation at Koudougou station and TEC map
shows that CODG model does not estimate Rinex TEC at Koudougou station.

Page(s): 617-623 2013/01/16 - 12:55

Title: Assessment of electromagnetic radiation from base station antennas

Authors: Singh, R K

Abstract: There is a strong
perception relating to existence of a high level of non-ionizing
electromagnetic radiation in the vicinity of base station antennas. In the
present paper, electromagnetic radiation from base station antennas installed
for various wireless communication purposes has been investigated based on
equivalent isotropically radiated power calculations. For this purpose, a
typical wireless communication site has been selected where GSM, CDMA, 3G/UMTS,
and WiMAX antennas are installed. The overall ratio of equivalent isotropically
radiated power (EIRP) and threshold EIRP combining all services at this
particular site has been calculated at ground level and nearby buildings. It
has been found that the ratio of EIRP and threshold EIRP is less than unity and
thus, the particular site is normally compliant and does not impose any adverse
health effects. For general public, the exclusion zone (compliance distance)
from GSM, CDMA, 3G/UMTS, and WiMAX antennas have been found at 7.30, 6.076,
7.436, and 6.861 m, respectively.

Page(s): 557-565 2012/11/15 - 03:28

Title: A search for precursors of earthquakes from multi-station ULF observations and TEC measurements in India

Authors: Chauhan, Vishal; Singh, O P; Pandey, Uma; Singh, Birbal; Arrora, B R; Rawat, Gautam; Pathan, B M; Sinha, A K; Sharma, A K; Patil, A V

Abstract: Ground based
observations have been carried out for ultra low frequency (ULF) precursors of
earthquakes at four different stations in India, namely Agra (geographic lat
27°N, long 78°E), Guttu (lat 31.53°N, long 78.75°E), Shillong
(lat 25.92°N, long 91.88°E) and Kolhapur (lat 16.40°N, long 74.15°E) using
identical 3-component search coil magnetometers (f = 0.01-30 Hz) obtained from
Lviv Centre of Space Research, Ukraine. An offline analysis of the combined
data has been carried out in relation to a major earthquake of magnitude M=7.9
occurred in the neighbouring country China (lat 31°N, long 103.32°E, depth=19
km) under the National Program of Earthquakes Precursors (NPEP) launched in
India since May 2009. The results of the analysis show occurrence of amplitude
anomalies as precursors whose amplitudes decrease with distance. The precursor
periods range between 2 and 5 days and are large for the stations nearer to
epicenter. A graphical determination of location of the epicenter has been found
to be satisfactory with errors within 20.5%. Further, the total electron
content (TEC) data obtained from a dual frequency GPS receiver at Agra station and global
ionospheric maps (GIMs) of TEC corresponding to the Wenchuan earthquake have
also been analysed. The GIM TEC data have been analysed for five different
locations which lie between Agra
and the epicenter of the earthquake. The anomalies in TEC data are investigated
by using quartile based statistical process. It has been found that GPS and GIM
TEC data show anomalous depletions of
02 - 13 days before and anomalous enhancements of 03 - 10 days prior to the
occurrence of earthquake.

Page(s): 543-556 2012/11/15 - 03:28

Title: Variability of the vertical extent of ionospheric E-layer over a station within equatorial anomaly region

Authors: Rabiu, A B; Abe, O E; Adeniyi, J O

Abstract: The variability of the vertical extent of
the E-layer of the ionosphere (VE) has been examined within the
equatorial ionospheric anomaly region, taken as the difference between 90 km
which is the assumed lower boundary of the layer and the virtual height values
measured with an ionosonde at Ouagadougou in Burkina Faso, West Africa
(geographic lat 12.4°N, long 1.5°W and magnetic dip 5.9°N) for low solar
activity year 1985 and high solar activity year 1990. The vertical extent is a
measure of the vertical altitude of E-region of the ionosphere. The vertical
extent of the E-layer was observed to be high (36-40 km) at sunrise and sunset
while low (18-22 km) at noon for both years. Seasonal variation shows that
vertical extent of E-layer during the solar minimum (maximum) is higher in
September (March) equinox and lower in March (September) equinox. The vertical extent of E-layer has been found to be
an unstable membrane as it varied from hour to hour, day to day, month to month
and season to season in response to the solar activity. The VE is
thicker in the low solar activity (26.30 ± 3.47 km) than the high solar
activity (23.01 ± 2.62 km), which implies that increase/decrease in the solar
activity results in decrease/increase in vertical extent of E-layer. Precisely,
5.4% (35.9%) variation in low (high) solar activity is accounted for by the
variability in solar activity while the remaining percentage may be due to
other factors.

Page(s): 536-542 2012/11/15 - 03:28

Title: Response of equatorial electrojet during the super geomagnetic storm of April 2000

Authors: Rastogi, R G; Chandra, H

Abstract: A major geomagnetic storm associated with
coronal mass ejection (CME) occurred with sudden commencement at
1636 hrs UT on 6 April 2000 and a minimum Sym/H index of -300 nT at 0000 hrs UT
on 7 April 2000. The event is unique with IMF Bz remaining southward from
around 1630 hrs UT till almost midnight. The event is studied from data at a
chain of ground magnetometers in the Indian and Pacific longitude sectors and
other low latitude stations. The amplitude of
SC (H) at low latitude stations was highest at Huancayo (around local mid-day)
with a value of about 150 nT and about
45 nT at Tirunelveli in the Indian sector (nighttime). The amplitude of SC in H
in the night side Indian sector showed an increase with latitude with a value
of about 45 nT near dip equator and increased to about 85 nT near Sq focus.
Counter electrojet was seen from 0400 to 1100 hrs UT (maximum value of -70 nT)
in the Indian sector and the ionograms at Thumba showed disappearance of Es-q
at 1130 hrs LT (0630 hrs UT) and its reappearance at 1630 hrs LT (1130 hrs UT).
The long duration counter electrojet in the Indian sector is likely due to
disturbance dynamo fields. Strong counter electrojet event from 0000 to 0300
hrs UT (maximum value of about -300 nT) in the far-east sector is probably due
to prompt penetration electric field (over shielding) associated with the
sudden northward turning of IMF Bz around midnight.

Page(s): 524-535 2012/11/15 - 03:28