Indian Journal of Radio & Space Physics


Total visitors: 944  since 13-04-06

(CODEN : IJRSAK        ISSN : 0367-8393)

VOLUME 35

NUMBER 2

APRIL 2006

 

CONTENTS

 

Guest Editorial: Effects of space weather events (SWE) at low latitude upper ionosphere/ atmosphere – Current issues

 

73

A R Jain*

 

 

Evening twilightglow of sodium 5893Å line emission at Calcutta and its typical relation with astronomical parameters

 

77

S K Midya* & R Chattopadhyay

 

 

Convection due to oblique magnetic field in the penumbral region of sunspot

84

B Shanker* & A Benerji Babu

 

 

Short period fluctuations in the equatorial electrojet electric fields

90

G Manju* & K S Viswanathan

 

 

A model of equatorial and low latitude VHF scintillation in India

98

K N Iyer, J R Souza, B M Pathan, M A Abdu, M N Jivani & H P Joshi*

 

 

Wind profiler radar for understanding the tropical convective boundary layer during different seasons

 

105

K Krishna Reddy*, Toshiaki Kozu & D Narayana Rao

 

 

Radiometric scene correction of temporal multi-spectral satellite data for crop discrimination

 

116

R N Sahoo*, R K Tomar, C S Rao, V K Sehgal, Nirupa Charchi, I P Abrol, M K Tiwari & M K Wadhawani

 

 

Reactively loaded annular ring microstrip antenna for multi-band operation

122

Binod K Kanaujia & Babau R Vishvakarma*

 

 

RF loss profile measurement for a high gain, broadband helix TWT

129

Vikas Kumar,  Anil Vohra* & Vishnu Srivastava

 

 

Theoretical analysis on circular sector microstrip antennas

133

V K Tiwari, Aradhana Kimothi, D Bhatnagar*, J S Saini, V K Saxena &
P Kumar

 

 

 

*Authors for correspondence

 

 


Indian Journal of Radio & Space Physics

Vol. 35, April 2006, pp. 77-83

 

 

Evening twilightglow of sodium 5893Å line emission at Calcutta and its typical relation with astronomical parameters

S K  Midya 1,2 & R  Chattopadhyay2,3

1Department of Physics, Serampore College, Serampore 712 201 Hooghly, West Bengal, India

2Centre for Space Physics, 43 Chalantika, Garia Station Road, Kolkata 700 084, India

3Haripal G D Institution, Khamarchandi, 712 405, Hooghly,West Bengal, India

Received 19 April 2004; received 22 March 2005; accepted 22 February 2006

Sodium line (5893 Å) represents one of the most important airglow emission lines. The photometric observations of evening twilightglow for this line were taken at Narendrapur (Lat. 22°35' Long. 88°21'E), a town in extended Calcutta, during the period between 1983 and 1988. Two distinctly recognizable enhancements or peaks were found to exist in time-versus-emission-intensity curve in evening twilight. One enhancement around sunset and the other a few minutes later were found to be a regular feature in everyday observation. On plotting the time of occurrence of the first peak relative to the sunset time for a complete month we obtained a sinusoidal curve having its troughs and crests coinciding with the different phases of the moon. This observation shows that the time of occurrence of the peak depends on the moon's age.

Keywords: Twilightglow; Sodium 5893Å line emission; Airglow emission lines

PACS No: 94.10Q, 94.20

 

 

 

 

Indian Journal of Radio & Space Physics

Vol. 35, April 2006, pp. 84-89

 

 

Convection due to oblique magnetic field in the penumbral region of sunspot

 

B Shanker1 & A Benerji Babu2

1Department of Mathematics, Nizam College, Osmania University, Hyderabad 500 007, India

2Department of Mathematics, University College of Science, Osmania University, Hyderabad 500 007, India

Received 24 September 2004; revised 13 January 2006; accepted 28 February 2006

The linear stability of convection due to oblique magnetic field in the penumbral region of sunspot has been investigated. We have obtained the values of Takens-Bogdanov bifurcation points and co-dimension two-bifurcation points by plotting graphs of neutral curves corresponding to stationary and oscillatory convection for different values of physical parameters relevant to convection in the penumbral region of sunspot.

Keywords: Convection, Penumbra, Bifurcation points

PACS No.: 96.60.Qc

 

 

  

 

Indian Journal of Radio & Space Physics

Vol. 35, April 2006, pp. 90-97

 

 

Short period fluctuations in the equatorial electrojet electric fields

G Manju & K S Viswanathan

Space Physics Laboratory, Vikram Sarabhai Space Centre, Trivandrum 695 022, Kerala, India

E-mail: manju_spl@vssc.org (Manju G)

Received 3 November 2005; accepted 14 February 2006

A study is made on the short period fluctuations in the equatorial electrojet parameters at the magnetic equatorial location of Trivandrum (8.5 °N, 77 °E; dip 0.5 °N), during daytime for a number of magnetically quiet days, using coherent VHF backscatter radar observations in the altitude region of 90-115 km. For this study ΔH values at and off equatorial latitudes have also been used. The detailed analysis of radar and magnetometer data show the following: (a) Significant fluctuation amplitudes in the period range of 25-35 min are present in the radar observations at different range bins over and above the dominant diurnal pattern of the height invariant large scale E-W electric field (Ey). The same periods do manifest when the radar data products are divided into sub-intervals of 1-1.5 h. (b) Values of H also indicate the same periods as that of radar observations. (c) A decrease in the amplitudes of the fluctuating components in H is seen from equator to low latitudes. The implications of the observations in terms of the possible origin of the fluctuations are discussed.

Keywords: Equatorial electrojet; Short period fluctuations; Type I irregularities; Type II irregularities;

           Coherent radar

PACS No: 84.40 Xb; 94.20.–y

 

 

Indian Journal of Radio & Space Physics

Vol. 35, April 2006, pp. 98-104

 

A model of equatorial and low latitude VHF scintillation in India

 

K N Iyer1, J R Souza2, B M Pathan3, M A Abdu2, M N Jivani1 & H P Joshi1

1Department of Physics and Electronics, Saurashtra University, Rajkot 360 005, India

2Instituto Nacional de Pesquisas Espaciais, São José dos Campos, São Paulo, Brazil

3Indian Institute of Geomagnetism, Colaba, Mumbai 400 005, India

Received 26 May 2005; revised 7 November 2005; accepted 6 March 2006

Using the observed VHF scintillations at equatorial and anomaly crest stations in India during the years 1987-1989, an empirical model is developed. The model employs the cubic spline technique to reproduce the variation of scintillation occurrence with local time, season, solar activity and latitude. The modelled values are compared with observed ones and the agreement is found to be quite good.

Keywords: Ionospheric scintillations, Scintillations, VHF scintillations, Cubic spline technique

PACS No.: 94.20.-y; 84.40.-x

 

  

 

Indian Journal of Radio & Space Physics

Vol. 35, April 2006, pp. 105-115

 

 

Wind profiler radar for understanding the tropical convective boundary layer during different seasons

K Krishna Reddy1, Toshiaki Kozu2 & D Narayana Rao3

1Institute of Observational Research for Global Change (IORGC)/Japan Agency for Marine-Earth Science and Technology
(JAMSTEC), Yokosuka, Japan

2Department of Electronic and Control Systems Engineering, Shimane University, Matsue, Japan

3National Atmospheric Research Laboratory (NARL), Gadanki, India

Received 8 September 2005; revised 22 December 2005; accepted 20 February 2006

This paper elucidates tropical continental boundary layer structures and their evolutions during different seasons over Gadanki, Southern India. Gadanki-LAWP (Lower Atmospheric Wind Profiler Radar) has proved to be an excellent tool for studying convective structures and boundary layer depth with good temporal (~ 10 min) and vertical resolution (150 m). We used LAWP reflectivity, Doppler velocity and spectral width data in time versus altitude to characterize general behaviour of convective boundary layer based on the “morning” and “evening” transition. From a wide variety of observed patterns, three categories are identified: (i) Descent, (ii) Ascent, and (iii) Inversion Layer (IL). Long-term Gadanki-LAWP observational results show the Ascent cases occur on relatively warm and moist days with strong turbulence and weak capping inversion [maximum occurrence in monsoon], descent days occur [pre-monsoon] on warm dry convection days and IL days occur [winter] on dew/fog and drier days with subsidence inversion and/or advection of warm air from the Bay of Bengal.

Keywords: Wind profiler radar, Boundary layer, Precipitation

PACS No.: 92.60.Ek; 94.10.Lf; 84.40.Xb

 

Indian Journal of Radio & Space Physics

Vol. 35, April 2006, pp. 116-121

 

Radiometric scene correction of temporal multi-spectral satellite data
for crop discrimination

R N Sahoo1, R K Tomar1, C S Rao1, V K Sehgal1, Nirupa Charchi2, I P Abrol2, M K Tiwari3 & M K Wadhawani4

1Division of Agricultural Physics, Indian Agricultural Research Institute, New Delhi 110 012

2Centre for Advancement of Sustainable Agriculture, NASC Complex, Pusa, New Delhi 110 012

3National Physical Laboratory, New Delhi 110 012

4Bihar Agricultural College, Sabour, Bhagalpur 813 210, Bihar

Received 13 August 2004; revised 7 February 2006; accepted 27 February 2006

Multi-date satellite images under different conditions of the same area are difficult to compare because of change in atmospheric propagation, sensor response and illuminations. To overcome this problem, a radiometric normalization technique, which is based on the statistical invariance of the reflectance of man-made in-scene elements (pseudo invariant features) was attempted. The LISS-III data of IRS-1D of three dates were taken for discrimination of crops and retrieval of crop statistics. To develop temporal NDVI profile of the various crop types, relative image-to-image radiometric scene normalization of each band was done using linear transformation. Water body, orchard and other less dynamic features were excluded and multidate-NDVI image having only agricultural crops was obtained for identification and classification of various crops. Nine classes were identified and discriminated as different crops by analyzing temporal NDVI profile pattern based on ground truth, crop calendar and information on crop sowing and harvesting time. Spatial distribution of different crops was analyzed and crop area statistics was computed.

Keywords:     Radiometric normalization, Pseudo-invariant features, Cropping pattern analysis, NDVI,

          Unsupervised classification

PACS No.:   95.40.+s

 

Indian Journal of Radio & Space Physics

Vol. 35, April 2006, pp. 122-128

 

Reactively loaded annular ring microstrip antenna for multi-band operation

 

Binod K Kanaujia

Department of Electronics and Communication Engineering, M. J. P. Rohilkhand University, Bareilly 243 006, India

E-mail: bkkanaujia@yahoo.co.in

and

Babau R Vishvakarma

Department of Electronics Engineering, Institute of Technology, Banaras Hindu University, Varanasi 221 005, India

Received 10 August 2004; revised 5 September 2005; accepted 28 September 2005

Reactively loaded probe-fed annular ring microstrip antenna (ARMSA) has been theoretically investigated for multi-band operation. The patch loaded with shorting post is analyzed taking the effect of feed probe into account. It is found that the resonance frequency of the patch increases with number of shorting pins and bandwidth of operation is also affected.

Keywords: Microstrip antenna, Annular ring antenna, Ring antenna, Patch antenna, Multi-band microstrip antenna

PACS No.: 84.40Ba

IPC Code: H01Q9/00; H01Q21/00; H01Q23/00

 

 

Indian Journal of Radio & Space Physics

Vol. 35, April 2006, pp. 129-132

 

 

RF loss profile measurement for a high gain, broadband helix TWT

Vikas Kumar

Amity Institute of Telecom Technology & Management, Sector-125, Noida (U.P.) 201 301, India

and

Anil Vohra

Electronic Science Department, Kurukshetra University, Kurukshetra, Haryana 136 119, India

and

Vishnu Srivastava

Microwave Tubes Area, Central Electronics Engineering Research Institute, Pilani, Rajasthan 333 031, India

E-mail: vk_aggarwal@rediffmail.com, vohras@sancharnet.in

Received 14 January 2005; revised 4 January 2006; accepted 16 February 2006

Helix type structure is widely used as slow wave structure in the travelling wave tube (TWT) due to its natural wide bandwidth. Reflections present in the structure may cause oscillations and hence instability in the device. In order to minimize the reflections, a coating of lossy material is done on the helix support rods in a TWT. The loss introduced by such coating has significant effects on the characteristics of the device. In the conventional methods the loss due to this coating (also known as the loss profiles) can be measured only on a single rod before fabrication of the slow wave structure (SWS) assembly. In the present work a new and convenient method has been developed for the measurement of loss profiles of a fabricated SWS assembly. Using the new method an experimental study has been made on a high gain TWT that is made in two sections with sever in between. The loss profiles along the axis of helical SWS have been measured at the sever end. This measurement is found to be very helpful to ensure the accuracy of the final fabricated assembly.

Keywords: Travelling wave tube, Helix, Reflections
           PACS No.:
84.40 Fe
           IPC Code:
H03F; H03 G3/00

Indian Journal of Radio & Space Physics

Vol. 35, April 2006, pp. 133-138

 

Theoretical analysis on circular sector microstrip antennas

 

V K Tiwari1, Aradhana Kimothi1, D Bhatnagar1, J S Saini1, V K Saxena1 & P Kumar2

1Department of Physics, University of Rajasthan, Jaipur 302 004, India

2Communication Systems Group, ISRO Satellite Center, Banglore 560 017, India

8 April 2005; revised 27 September 2005; accepted 3 March 2006

A rigorous theoretical analysis of a circular sector microstrip antenna with sector angle a is carried out. General expressions for radiated fields by antenna are derived by applying cavity model based modal expansion technique and are used to study its radiation parameters. Similar to a circular disk antenna, better results for circular sector antenna are also obtained in TM11 mode of excitation. The computed results of a sector antenna with a = 60° are compared with simulation results and a difference of 2.5%, 38%, 7% and 1.9%, respectively in resonance frequency; input impedance, directivity and bandwidth is recorded.

Keywords: Microstrip antenna, Circular sector microstrip antenna, Cavity model and radiation patterns, Resonance frequency; Input impedance, Directivity, Bandwidth

PACS No.: 84.40 Ba, 75.50 Gg