MARC details
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| fixed length control field |
04670nam a2200229Ia 4500 |
| 003 - CONTROL NUMBER IDENTIFIER |
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| control field |
IN-BaIIA |
| 005 - DATE AND TIME OF LATEST TRANSACTION |
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| control field |
20211109164824.0 |
| 008 - FIXED-LENGTH DATA ELEMENTS--GENERAL INFORMATION |
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| fixed length control field |
211028s9999 xx 000 0 eng d |
| 040 ## - CATALOGING SOURCE |
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| Transcribing agency |
IIA Library |
| 080 ## - UNIVERSAL DECIMAL CLASSIFICATION NUMBER |
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| Universal Decimal Classification number |
043:523.947 |
| Item number |
RAM |
| 100 ## - MAIN ENTRY--PERSONAL NAME |
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| Personal name |
Ramesh, R. |
| 9 (RLIN) |
23453 |
| Relator term |
Author |
| 245 #0 - TITLE STATEMENT |
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| Title |
Multi-frequency observations of the outer solar corona with the Gauribidanur radioheliograph. Ph. D. Thesis |
| Statement of responsibility, etc. |
R. Ramesh |
| Medium |
[Ph.D Thesis] |
| 260 ## - PUBLICATION, DISTRIBUTION, ETC. |
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| Place of publication, distribution, etc. |
Bangalore |
| Name of publisher, distributor, etc. |
Indian Institute of Astrophysics |
| Date of publication, distribution, etc. |
1998 |
| 300 ## - PHYSICAL DESCRIPTION |
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| Extent |
172p |
| 502 ## - DISSERTATION NOTE |
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| Degree type |
Doctor of Philosophy |
| Name of granting institution |
Indian Institute of Astrophysics, Bangalore |
| Year degree granted |
1998 |
| 520 ## - SUMMARY, ETC. |
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| Summary, etc. |
A new radioheliograph dedicated to observations of the outer corona of the<br/>Sun has been built by the Indian Institute of Astrophysics at the Gauribidanur<br/>radio observatory and is in operation since April 1997. This instrument<br/>(hereafter referred to as the Gauribidanur radioheliograph, GRH) is capable<br/>of producing two-dimensional pictures of the solar corona in the frequency<br/>range 40 - 150 MHz (a height range of R:i 0.1 - 0.6 R8 above the photosphere).<br/>At present this is the only instrument of its kind in the world in the<br/>above frequency range for regular observations of the Sun.<br/>The GRH is a T-shaped array with a long E-W arm and a short South<br/>arm. It works on the well known principles of synthesis imaging where the<br/>outputs from the individual antenna groups are taken separately to the receiver<br/>building and fed to a receiver system which measures the spatial coherence<br/>between the received signals. Since the GRH has 32 antenna groups<br/>(16 E-W + 16 South), a 1.024 channel digital receiver is used to correlate the<br/>signals received by the different antenna groups. Included in this thesis is a<br/>description of the receiver system and its various sub-units. The details of<br/>the Walsh switching scheme and its effectiveness in removing the contribution<br/>from unwanted signals are described. The tests carried out to measure<br/>the cross-talk between the input signals to the correlator, DC offset in the<br/>A / D convertors, effects of the res ideal errors in the correlator system on the<br/>measured visibilities in the u-v plane a.re discussed in detail.<br/>One of the biggest challenges in the synthesis imaging of any radio source is<br/>the removal of instrumental propagation errors from the observed quantities.<br/>There are several techniques in use at present which derive the correction<br/>terms frorn the observed quantities themselves. Some of the practical and<br/>technical problems in applying the existing techniques to solar observations with arrays like the GRR and the details of the scheme that we have developed<br/>are given. The successful use of our scheme in practice is illustrated<br/>by comparing the maps obtained with the GRR with those made at other<br/>wavelengths as well as using other techniques. A quantitative estimate of the<br/>possible errors in the present scheme is also carried out.<br/>The estimation of electron density at various heights in the ambient corona<br/>as well as above the active regions is generally done using density models<br/>derived from the white light data obtained during solar eclipses and using<br/>coronographs. From radio observations, it is possible to calculate the altitude<br/>of the emitting regions and the density, in an independant way, if the source<br/>under observation shows regular movement across the solar disk. Using the<br/>one-dimensional observations carried out with the E-W arm of the GRR at<br/>51 and 77 MHz, the altitudes of the plasma levels at these frequencies are<br/>derived.<br/>Two-dimensional maps obtained with the GRR on quiet days when no<br/>non-thermal emission (burst activity) was seen in our records, were used<br/>to study the thermal emission from the undisturbed corona. The effects of<br/>coronal streamers, holes, and scattering by small-scale density in homogeneities<br/>in the corona OIl the observed quiet Sun emission and the low values of<br/>the observed brightness temperature are discussed.<br/>An understanding of coronal mass ejections (CMEs) and its origin is one<br/>of active areas of research in the field of solar physics. An attempt has been<br/>made to identify the pre-event signatures of the CMEs from the radio data<br/>observed with the GRIT. In one case study, the mass of the coronal material<br/>that was associated with a halo CME has been estimated from the global<br/>restructuring of the corona in the aftermath of the event. |
| 650 ## - SUBJECT ADDED ENTRY--TOPICAL TERM |
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| Topical term or geographic name entry element |
solar corona |
| 650 ## - SUBJECT ADDED ENTRY--TOPICAL TERM |
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| Topical term or geographic name entry element |
thesis |
| 9 (RLIN) |
18401 |
| 700 ## - ADDED ENTRY--PERSONAL NAME |
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| Personal name |
R. Cowsik |
| Relator term |
Supervisor |
| 9 (RLIN) |
48862 |
| 856 ## - ELECTRONIC LOCATION AND ACCESS |
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| Uniform Resource Identifier |
<a href="http://prints.iiap.res.in/handle/2248/99">http://prints.iiap.res.in/handle/2248/99</a> |
| Link text |
Click Here to Access eThesis |
| 942 ## - ADDED ENTRY ELEMENTS (KOHA) |
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| Koha item type |
Thesis & Dissertations |
| Source of classification or shelving scheme |
Universal Decimal Classification |
