Indian Journal of Radio & Space Physics
VOLUME 30
NUMBER 4
AUGUST 2001
CONTENTS
Strength of equatorial electrojet and geomagnetic activity control on VHF
scintillations at the Indian longitudinal zone
S Banola , B M Pathan & D R K Rao
163
Comparison of total electron content predicted by IRI with that measured over Ankara
Osman Özcan & İbrahim Ünal
172
Short-term ozone trend in India
P K Jana , S K Midya & U K De
176
Sodar observed winds in the convective boundary layer at Kharagpur , India, during
monsoon 1990
B S Murthy & S S Parasnis
Multipath effects on a line-of-sight microwave link
S K Sarkar , K Megha Raju , D Punyaseshundu ,M M Gupta , Rajesh Kumar
& M V S N Prasad
Response of microwave scattering from crop (wheat) and crop covered soil moisture
for remote sensing
D Singh , S K Sharan & K P Singh
Triangular microstrip stacked antenna for dual band operation
Prashant Vasistha & Babau R Vishvakarma
181
194
198
205
Notes
Ionospheric electron content near anomaly crest as precursor of earthquake
M Devi , M K Barman , A K Barbara & A Depueva
Characteristics of the observed low latitude very low frequency emission periods and
whistler-mode group delays at Jammu
Lalmani , Rajou Kumar , Rajesh Singh & Birbal Singh
1
209
214
Indian Journal of Radio & Space Physics
Vol. 30, August 2001, pp. 163-171
Strength of the equatorial electrojet and geomagnetic activity
control on VHF scintillations at the Indian longitudinal zone
S Banola, B M Pathan & D R K Rao
Indian Institute of Geomagnetism, Colaba, Mumbai 400 005
Received 5 April 2000; revised 2 March 2001; accepted 3 April 2001
Amplitude scintillations on 244 MHz radio signals transmitted from geo-stationary satellite,
FLEETSAT (73E), were continuously recorded at a network extending from Ujjain (situated north of
anomaly crest region) to the equatorial station, Trivandrum, by the Indian Institute of Geomagnetism,
Mumbai. Parameters of geomagnetic activity like K-Alibag, Ap and electrojet strength are used to study
the association of the amplitude scintillation recordings at the equatorial station, Trivandrum ( dip 1 N )
and at Mumbai ( dip 26 N ), a station south of the anomaly crest region during the high solar activity
period 1989-1991. It is observed that an increase in geomagnetic activity (K-Alibag or Ap) suppresses the
occurrence of scintillation activity at both the stations, whereas the electrojet strength is found to have no
association on the occurrence of scintillations. A total of 77 storms occurring during this period are
classified into three types according to Aarons criterion. The time of the maximum intensity of ring
current appears to play a role directly or indirectly in establishing the conditions necessary for the
equatorial F-layer irregularity generation and inhibition which, in turn, manifests itself in scintillation
activity. However, there is about 30-40 % of scintillation activity unaccounted by the magnetospheric
electric field alone.
Indian Journal of Radio & Space Physics
Vol. 30, August 2001, pp. 172-175
Comparison of total electron content predicted by IRI with
that measured over Ankara
Osman Özcan & Ïbrahim Ünal
Department of Physics, Faculty of Arts and Science, Firat University, 23119 Elazig-Turkey
Received 30 August 2000; revised 12 January 2001; accepted 20 March 2001
The total electron content (TEC) is a very important parameter for the systems that use
transionospheric radio waves. In this paper, TEC measurements obtained with Faraday technique at
Ankara (geogr. lat. 40o N, geogr. long. 33o E, geomagn. lat. 36.9o N, dip angle 56.7o) are compared with
the TEC obtained by using the International Reference Ionosphere (IRI) model to check the performance
of IRI for predicting TEC over this station. The measurements have been taken between October 1975 and
June 1976 during low solar activity period. In general, the IRI model was found to give good predictions
except for spring equinox and summer solstice time.
Indian Journal of Radio & Space Physics
Vol. 30, August 2001, pp. 176-180
2
Short-term ozone trend in India
P K Jana
Department of Chemistry, Howrah Zilla School,Howrah 711 101
and
S K Midya
Department of Physics, Serampore College, Serampore, Hooghly 712 201
and
U K De
Environmental Science Program, Jadavpur University, Calcutta 700 032
Received 14 March 2000; Revised received 30 October 2000; accepted 17 April 2001
This paper presents the variation of ozone concentrations at different stations in India and average
variation of O3 concentration over India. The results are also compared with those of Halley Bay (76S,
27W), a British Antarctic Survey Station.
Indian Journal of Radio & Space Physics
Vol. 30, August 2001, pp. 181-193
Sodar observed winds in the convective boundary layer at Kharagpur,
India, during monsoon 1990
B S Murthy & S S Parasnis
Indian Institute of Tropical Meteorology, Pune 411 008
Received 21 August 2000; revised 17 January 2001; accepted 19 March 2001
Sodar has been installed at Kharagpur (22.2 N, 87.3 E) as a part of the Monsoon Trough Boundary
Layer Experiment (MONTBLEX-90) and data were collected during the monsoon period. The monthlymean wind field variation in the convective boundary layer (CBL) at Kharagpur during the S-W monsoon
of 1990 has been studied. Monthly-mean horizontal winds were found to be westerly/north-westerly in the
convective boundary layer above ~ 600 m in all the monsoon months. In August, mean winds near the
surface have become easterly in response to the monsoon depressions formed in the north Bay of Bengal
during 15-31 Aug. 1990. Two case studies of depression are studied in terms of winds and thermal
structure in the convective boundary layer at Kharagpur. The variation of CBL height over Kharagpur
during the onset, active and low/depression phases of the monsoon 1990 is also presented.
Indian Journal of Radio & Space Physics
Vol. 30, August 2001, pp. 194-197
Multipath effects on a line-of-sight microwave link
S K Sarkar1, K Megha Raju2, D Punyaseshundu2, M M Gupta1, Rajesh Kumar1 & M V S N Prasad1
1Radio
& Atmospheric Sciences Division, National Physical Laboratory,
Dr K. S. Krishnan Road, New Delhi 110 012
2Department of Physics, S K University, Kurnool 518 001
Received 12 May 2000; revised 14 December 2000; accepted 18 April 2001
3
The effects of multipath in relation to the deteriorated performance of a microwave communication
link situated between Guntakal and Adoni over the Indian southern region have been investigated. The
received signal level under normal condition is usually found to be around 60 dBm. The performance of
the link is satisfactory when the signal level is equal to and greater than 74 dBm, which is the
satisfactory level of the signal. It has been seen that the link performance starts deteriorating when the
signal level reduces to as low as around 75 dBm. The most problematic months during which the
performance of the radio link is not up to the satisfactory level are found to be from November to May.
The peaks of the disturbances are in the months of February through May. The performance of the link
has been found to be disturbed during 2300-0800 hrs LT. On the basis of low signal level (multipath
fading), causes of deterioration in relation to meteorological conditions have been determined. In order to
counter multipath fading, some techniques have been discussed in this paper. In future this study can also
be taken as a reference for designing the microwave communication systems located in the Indian
southern region. It is suggested that the link should be equipped with some diversity system.
Indian Journal of Radio & Space Physics
Vol. 30, August 2001, pp. 198-204
Response of microwave scattering from crop (wheat) and crop covered
soil moisture for remote sensing
D Singh & S K Sharan
Govt. P G Science College, Seepat Road, Bilaspur (CG) 495 006
and
K P Singh
Department of Electronics Engineering, Banaras Hindu University, Varanasi, (U.P) 221 005
Received 7 February 2000;revised 17 January 2001;accepted 1 March 2001
The present study investigates the potential use of active microwave observations at 9.5 GHz
frequency of X-band to monitor soil moisture and vegetation leaf area index (LAI) over a wheat cover for
remote sensing. Using an X-band (9.5GHz) scatterometer, measurements have been made out for different
growth stage of crop (wheat). The leaf area index (LAI) is an important parameter for understanding the
crop characteristics. Here an attempt has been made to highlight the effect of crop (wheat) LAI and crop
covered soil moisture (mg) on microwave scattering. Using simple scattering model, an empirical relation
has been developed for observing the LAI and mg effect on scattering coefficient. The angular and
polarization dependence of scattering coefficient on crop LAI and crop covered soil moisture has been
investigated, which indicates that, when incidence angle is less than 30, the crop (wheat) covered soil
moisture is well observed, whereas when the incidence angle is greater than 30, crop effect is more
dominant at 9.5 GHz. The VV-polarization is more sensitive to sense the crop effect than HHpolarization. This type of study is helpful to make the algorithm for air- or space-borne data to access the
crop parameters and crop covered soil moisture. All these data can also be used as reference data for
space-borne sensors.
Indian Journal of Radio & Space Physics
Vol. 30, August 2001, pp. 205-208
Triangular microstrip stacked antenna for dual band operation
4
Prashant Vasistha & Babau R Vishvakarma
Department of Electronics Engineering, Institute of Technology, Banaras Hindu University, Varanasi 221 005
Received 31 July 2000; revised received 8 January 2001
Experimental investigations conducted on triangular microstrip stacked antenna (TMSSA) to achieve
dual band operation by optimizing the number of elements reveal that TMSSA attains the maximum 10
dB return-loss band of 688.6 MHz for (1+3) structure for second resonance. The air gap spacing of 2.5
mm in (1+1) structure improved 10 dB return-loss (RL) band by 612.14 MHz as compared to 242.3
MHz for zero spacing in first resonance (fr1). It is also observed that 10 dB return-loss band depends
heavily on the angular rotation (non-alignment) in the (1+1) structure.
Indian Journal of Radio & Space Physics
Vol. 30, August 2001, pp. 209-213
Notes
Ionospheric electron content near anomaly crest as precursor of earthquake
M Devi, M K Barman & A K Barbara
Department of Physics, Gauhati University, Guwahati 781 014
and
A Depueva
IZMIRAN, Troitsk Moscow Region, Russia 142 092
Received 3 November 2000; revised received 28 February 2001
Ionospheric electron content (IEC) values, derived from Faraday rotations of VHF radio beacons from satellites
and recorded at an equatorial anomaly crest station, Guwahati (lat.26.2 N, long.91.75E; and situated at a seismically
active zone of east Himalayas), have been examined to see if these data could be used as precursor of earthquake. The
earthquake events are so selected that the epicentres lie within 12-30 N and 81-120 E. The paper analyses IEC
variations during and prior to an earthquake event, in relation to epicentric position.
Indian Journal of Radio & Space Physics
Vol. 30, August 2001, pp. 214-216
Characteristics of the observed low latitude very low frequency emission
periods and whistler-mode group delays at Jammu
Lalmani1, Rajou Kumar1, Rajesh Singh2 & Birbal Singh3
1Department
of Physics, Engineering College, Srinagar,
Camp Jammu, Canal Road, Jammu 180 001
2Atmospheric Research Laboratory, Physics Department,
Banaras Hindu University, Varanasi 221 005
3Department of Physics, R .B .S. College, Agra 282 002
Received 29 May 2000; revised 14 September 2000;
accepted 28 March 2001
First observations on the relationship between whistlers and periodic very low frequency (VLF) emissions
5
observed at low latitude ground station Jammu (geomagn. lat., 22 26 N; L = 1.17) are presented. The results have been
discussed in the present paper. To explain the results it is proposed that the periodic VLF emissions are generated near
the equatorial region at L ~ 1.2 as a result of interaction between trapped energetic particles and one-hop whistlers
under cyclotron resonance mechanism and propagated to the ground station Jammu in nonducted mode of whistler
propagation.
6