Indian Journal of Radio & Space Physics

Total visitors: 284 since 14-08-07

(CODEN : IJRSAK        ISSN : 0367-8393)

VOLUME 36

NUMBER 4

AUGUST 2007

 

CONTENTS

 

Preface

 

243

Guest Editorial: Need for space technology and its impact on our lives

        Kumar Krishen*

 

245

 

Special Supplement

 

 

An overview of GBAS integrity monitoring with a focus on ionospheric spatial anomalies

        Sam Pullen* & Per Enge

 

 

249

 

 

IGS network: Application of GPS to geodesy

        Angelyn W Moore*

 

261

 

Characteristics of the ionospheric F-region plasma irregularities over Brazilian longitudinal sector

E R de Paula*, E A Kherani, M A Abdu, I S Batista, J H A Sobral, I J Kantor,
H Takahashi, L F C de Rezende, M T A H Muella, F S Rodrigues, P M Kintner,
B M Ledvina, C Mitchell & K M Groves

 

 

268

 

Ionospheric total electron content (TEC) studies with GPS in the equatorial region

      A DasGupta*, A Paul & A Das

 

278

 

GAGAN — The Indian satellite based augmentation system

        K N Suryanarayana Rao*

 

293

Time transfer through GPS

        P Defraigne, P Banerjee* & W Lewandowski

 

303

 

Regular Papers

 

 

Some aspects of equatorial electrojet in South America

        R G Rastogi*

 

315

Whistler wave instability and plasma sheet ALC distribution at substorm onsets

        P R Prince* & G Renuka

 

318

Variability of millimetrewave rain attenuation and rain rate prediction: A survey

        R Bhattacharya*, R Das, R Guha, S Deb Barman & A B Bhattacharya

 

325

 

Nickel and iron as attenuator materials for helix TWT

        Vikas Kumar*, Anil Vohra & Vishnu Srivastava

 

345

___________________

*Authors for correspondence

 

 


Indian Journal of Radio & Space Physics

Vol. 36, August 2007, pp 249-260

 

An overview of GBAS integrity monitoring with a focus on
ionospheric spatial anomalies

 

Sam Pullen & Per Enge

Department of Aeronautics and Astronautics, Stanford University, USA

E-mail: spullen@stanford.edu

Received 2 April 2007; accepted 14 May 2007

The Local Area Augmentation System (LAAS) or, more generally, the Ground Based Augmentation System (GBAS), has been developed over the past decade to meet the accuracy, integrity, continuity and availability needs of civil aviation users. The GBAS utilizes a single reference station (with multiple GNSS receivers and antennas) within an airport and provides differential corrections via VHF data broadcast (VDB) within a 50-km region around that airport. This paper provides an overview of GBAS integrity verification, explaining how integrity risk is allocated to various potential safety threats and how monitors are used to meet these allocations. In order to illustrate GBAS integrity monitoring in detail, this paper examines the potential threat of ionospheric spatial anomalies (e.g., during ionospheric “storms”) to GBAS and how GBAS protects users against this threat. In practice, the need to mitigate potential ionospheric anomalies is what dictates CAT I GBAS availability.

Keywords: LAAS, GBAS, Ionospheric spatial anomalies, Civil aviation

PACS No: 94.20.Vv; 94.20Bb

 

Indian Journal of Radio & Space Physics

Vol. 36, August 2007 pp. 261-267

 

IGS network: Application of GPS to geodesy

Angelyn W Moore

International GNSS Service Central Bureau, Jet Propulsion Laboratory, California Institute of Technology
4800 Oak Grove Dr. MS 238-540, Pasadena, CA 91109, USA

Received 22 March 2006; accepted 14 May 2007

The Global Positioning System's satellites transmit time-dependent signals on two frequencies. When received on the ground and analyzed, these signals yield many benefits to geodesy, including terrestrial reference frames, plate and local motion, earth rotation parameters, and atmospheric information. The International GPS Service self-organized to efficiently coordinate a worldwide reference network of stations and analyze the data through international, voluntary collaboration. The products of this analysis are geodetically significant in themselves, and are used to great advantage by investigators in focused studies.

Keywords: Global Positioning System (GPS), International GPS Service (IGS), International GNSS Service (IGS), Very Long Baseline Interferometry (VLBI), TRANSIT, Global Navigation Satellite System (GNSS), GLONASS satellite system, Galileo satellite system, International Terrestrial Reference Frame (ITRF)

PACS No.: 91.10.Vr

 

Indian Journal of Radio & Space Physics

Vol. 36, August 2007, pp. 268-277

 

Characteristics of the ionospheric F-region plasma irregularities over Brazilian longitudinal sector

E R de Paula1, E A Kherani1, M A Abdu1, I S Batista1, J H A Sobral1, I J Kantor1, H Takahashi1, L F C de Rezende1,
M T A H Muella1, F S Rodrigues1, P M Kintner2, B M Ledvina2, C Mitchell3 & K M Groves4

1INPE-National Institute for Space Research, Av. dos Astronautas 1758, 12.227-010 São José dos Campos, São Paulo, Brasil

2Department of Electrical and Computer Engineering, Cornell University, Ithaca, New York, USA

3 Department of Electronic and Electrical Engineering, Bath University, Bath, UK

4 Space Vehicles Directorate, Air Force Research Laboratory, Hanscom Air Force Base, Massachusetts, USA

Received 2 April 2007; accepted 14 May 2007

Based on the data obtained from a network of GPS L1 band receivers deployed in Brazil, are presented here the characteristics of the 400 m ionospheric irregularities during magnetically quiet and disturbed conditions. The network is composed of 12 GPS scintillation monitors and covers the latitudinal region from the magnetic equator up to the southern crest of the Equatorial Ionization Anomaly (EIA), which is characterized by large horizontal gradients in the electron density distribution. Some results on equatorial spread-F statistics obtained from digisonde data over Cachoeira Paulista (22.41o S, 45o W, dip latitude 14.89o S) and from ionosonde data over Tucumán (64.5o W, 27o S, dip latitude 13.71o S) are also used in this work to complement the results from GPS network. The effects of local time, season, latitude, longitude, background ionization, solar cycle and magnetic activity on the ionospheric irregularities are presented. The ionospheric irregularity zonal velocities determined by magnetically east-west spaced GPS receivers are also presented. The influence of the ionospheric irregularities on GPS based navigational systems is discussed. These observations, complemented by computational simulations, may improve our understanding of the factors responsible for the generation, growth and dynamics of the equatorial F-region plasma irregularities.

Keywords: Ionospheric plasma irregularities, GPS scintillation monitor, Space based augmentation system (SBAS)

PACS No.: 94.20.Yx; 94.20.Vv; 94.20.Ww

 

Indian Journal of Radio & Space Physics

Vol. 36, August 2007, pp. 278-292

 

Ionospheric total electron content (TEC) studies with GPS in the
equatorial region

 

A DasGupta1, 2, A Paul2 & A Das1

1 S K Mitra Center for Research in Space Environment, University of Calcutta, 92 A P C Road, Calcutta 700 009, India

2 Institute of Radio Physics and Electronics, University of Calcutta, 92 A P C Road, Calcutta 700 009, India

Email: adg1bkpr@hotmail.com

Received 2 April 2007; accepted 14 May 2007

This paper essentially deals with the effects of equatorial ionization anomaly gradient on space-based navigation systems like GPS. The equatorial region of the ionosphere, which extends about ±30odip about the magnetic equator, is characterized by a steep latitudinal gradient, not only in the maximum ionization but also in the total electron content (TEC), through a major part of the day. This region also accounts for about one-third of the global electron content. The high ambient TEC results in large range errors for a major part of the day, affecting navigation and position-fixing using GPS. The gradient of the equatorial ionization anomaly between the trough and the crest is very sharp, which results in large temporal and spatial variation of the ionospheric electron content. A prediction of the range error introduced by the ionosphere in the equatorial zone is very difficult. Identification of a suitable ionospheric model for prediction of these errors in the geophysically sensitive equatorial region is necessary prior to the introduction of Indian SBAS network, GAGAN (GPS And Geo Augmented Navigation). For this purpose, ionospheric TEC measured from Calcutta, situated underneath the northern crest of the equatorial anomaly, has been compared with values generated by models like PIM1.6 and IRI-95 during 1977-1990. The equatorial anomaly gradient not only extends in the horizontal direction but with altitude also. Problems related to conversion of vertical to slant TEC and vice versa, as required for ionospheric range error corrections in satellite-based navigation with GPS, have been indicated and diagnostics suggested. It has been observed that sharp latitudinal gradient of TEC during the afternoon hours of equinoctial months of high sunspot number years is usually followed by generation of irregularities over the magnetic equator in the form of ‘bubbles’ or depletions. These depletions have sharp edges resulting in large range error rates on GPS links. Characteristics of bubbles, namely, amplitude and leading and trailing edge slopes, have been studied using GPS TEC data recorded at the Giant Meterwave Radio Telescope (GMRT) site during the vernal equinox of 2004. Use of GPS TEC measurements as a tool for studying ionospheric response to earthquakes has also been indicated.

Keywords:   Total electron content (TEC), Global positioning system (GPS), Ionospheric TEC, GAGAN, SBAS, GMRT

PACS No.: 94.20.Yx; 94.20.Vv; 94.20.Ww

 

Indian Journal of Radio & Space Physics

Vol. 36, August 2007, pp. 293-302

 

 

GAGAN - The Indian satellite based augmentation system

K N Suryanarayana Rao

ISRO Satellite Centre, Airport Road, Bangalore 560 017, India

Received 2 April 2007; accepted 14 May 2007

Global Positioning System (GPS) from the USA, Global Navigation Satellite System (GLONASS) from the Russian Federation and the proposed GALILEO satellite navigation system from Europe are meant for providing position and timing information for a variety of applications. However, for Safety Critical applications the basic constellations cannot meet the requirements in terms of accuracy, integrity and availability. For this purpose, the basic constellations are augmented by an overlay system. Indian Space Research Organization (ISRO), along with Airport Authority of India (AAI) is implementing the Satellite Based Augmentation System (SBAS) for the Indian region. The project called GAGAN (GPS Aided Geo Augmented Navigation) has a full complement of the SBAS inclusive of ground and onboard segment. The first phase of GAGAN is nearing completion. This paper deals with the basic SBAS concept, GAGAN configuration, implementation and the challenges involved. The roadmap towards the final operational phase is also indicated.

Keywords: GAGAN, Global Navigation Satellite System (GNSS), Satellite based augmentation system (SBAS), Indian Master Control Station (INMCC), Indian Reference Station (INRES)

PACS No.: 84.40.Ua

 

 

Indian Journal of Radio & Space Physics

Vol. 36, August 2007, pp. 303-312

 

 

Time transfer through GPS

P Defraigne1, P Banerjee2 & W Lewandowski3

1Royal Observatory of Belgium, Ringlaan 3, B-1180 Brussels, Belgium

2Time and Frequency Section, National Physical Laboratory, Dr K S Krishnan Road, New Delhi 110 012, India

3Bureau International des Poids et Mesures, Pavillon de Breteuil, 92310, Sèvres, France

Received 19 June 2007; accepted 17 July 2007

Commonly available GPS receivers have, these days, hardware outputs of 1 pps. These receivers normally have the time accuracy within 100 ns. But if these are not calibrated in advance, they cannot be recommended for precise on-line applications. However, common view mode GPS time transfer using single satellite is in use for the generation of Coordinated Universal Time (UTC) by ensembling more than 40 clocks scattered all over the world. Use of carrier phase in common view mode is being explored. The initial results are quite encouraging. The paper reviews the current status of these time transfer techniques via GPS.

Keywords: Global positioning system (GPS), Coordinated universal time (UTC), International atomic time (TAI), Two-way satellite time and frequency transfer (TWSTFT)

PACS No.: 95.75.Wx; 06.30.Ft

 

Indian Journal of Radio & Space Physics

Vol. 36, August 2007, pp. 315-317

 

 

Some aspects of equatorial electrojet in South America

R G Rastogi

Physical Research Laboratory, Ahmedabad 380 009, India.

Received 19 December 2005; revised 22 November 2006; accepted 19 March 2007

The strength of the equatorial electrojet is shown to be stronger at 75oW longitudes than at 45oW longitudes inspite of the magnetic field intensity being lower along 45oW than 75oW longitudes. There was significant correspondence in the day-to-day variation of the daily range as well as in the character of daily variation of the horizontal geomagnetic field, H, at two equatorial electrojet stations separated by 30o in longitude.

Keywords: Equatorial electrojet, Geomagnetic field, Ionospheric conductivities

PACS No. : 94.20 Yx; 94.20 Vv; 94.20 Ss

 

 

Indian Journal of Radio & Space Physics

Vol. 36, August 2007, pp. 318-324

 

 

Whistler wave instability and plasma sheet ALC distribution at substorm onsets

P R Prince

School of Technology and Applied Sciences, Mahatma Gandhi University, Regional Centre, Pathanamthitta, Kerala 689 645

and

G Renuka

Department of Physics, University of Kerala, Thiruvananthapuram 695 581

e-mail: drprprince@yahoo.com

Received 23 March 2006; revised 13 March 2007; accepted 17 April 2007

Whistler waves interacting with an assumed anti-loss cone (ALC) distribution is shown to become highly unstable at times of substorm onsets. This establishes the presence of ALC electrons at onset-time geomagnetosphere plasma sheet (PS). The stability analysis proves that the whistler instability resulting from ALC interactions arises at frequencies greater than the electron cyclotron frequency. The study establishes the role of   plasma b as a factor determining the extent of whistler instability even at times of highly disturbed conditions. The major part of free energy available at PS during substorm onsets is proved to be the contribution due to the anisotropy of the ALC distribution function. Presence of a few cold electrons along with hot ALC plasma is shown to cause wave decay.

Keywords: Whistlers, Anti-loss cone, Plasma instability, Substorms, Particle distributions.

PACS No.: 52.35.Py

 

 

Indian Journal of Radio & Space Physics

Vol. 36, August 2007, pp. 325-344

 

 

Variability of millimetrewave rain attenuation and rain rate prediction: A survey

R Bhattacharya, R Das, R Guha & S Deb Barman

Department of Environmental Science, University of Kalyani, Kalyani 741 235, India

and

A B Bhattacharya

Department of Physics, University of Kalyani, Kalyani 741 235, India

Received 24 May 2006; revised 31 January 2007; accepted 3 May 2007

This paper reviews the literature on attenuation of mm-wave due to rain and rain rate prediction methods to analyze the performance of the various systems proposed by different workers at different parts of the globe under varying meteorological and topographical conditions with an emphasis on the observational reports made in the tropics, particularly in the Indian subcontinent. In this comprehensive review, besides considering the various features related to rain rate, the various methods proposed for prediction of rain attenuation have been examined and thereby a comparison of those prediction methods is made. Finally, scopes for future investigation have been critically focused.

Key words: Rain attenuation, rain rate, millimetrewave

PACS No.: 92.60. Ta

  

Indian Journal of Radio & Space Physics

Vol. 36, August 2007, pp. 345-347

 

 

Nickel and iron as attenuator materials for helix TWT

Vikas Kumar1, Anil Vohra2 & Vishnu Srivastava3

1Asia-Pacific Institute of Management, Jasola, Sarita Vihar, New Delhi 110 025, India

2Electronic Sc. Department, Kurukshetra University, Kurukshetra, Haryana 136 119, India

3Microwave Tubes Area, CEERI, Pilani, Rajasthan 333 031, India

E-mail: vk_aggarwal@rediffmail.com, vohra64@gmail.com

Received 27 July 2006; revised 12 January 2007; accepted 5 March 2007

Coating of lossy material is done on the helix support rods to absorb reflections in a helix travelling wave tube. Carbon is a very commonly-used material used for this type of coating, but other materials may also be employed for this purpose. In the present work coatings of carbon, nickel and iron have been done and evaluated for the attenuation performance at microwave frequencies. Three alumina rods have been coated with different methods to characterize them for attenuation. One alumina rod has been coated with carbon using the pyrolytic deposition method, while two others have been coated with iron and nickel using the electro-deposition method. An experimental set-up involving a narrow-height waveguide with a hole was used to measure the attenuation of the coated rods at 6.0 GHz frequency.

Keywords: Attenuator materials, Travelling wave tube, Helix, Reflections

PACS No.: 42.68 Ay; 94.10Gb

IPC Code: H01P 5 / 00