FUTURE PLANS AND
TECHNICAL DEVELOPMENTS
FOR THE SIBERIAN SOLAR RADIO TELESCOPE
The development of the large radio telescope
project, designed for addressing the problems in the physics of the solar
corona, was conceived at the beginning of the 1960s with the purpose of
switching over from recording of active regions and flares using their integral
emission to a systematic study of the atmospheric structure of active regions,
the spatio-temporal processes of emergence of magnetic fluxes and their
interaction, to identification of flare buildup signatures, and to the
localization of energy storage and release regions. Incidental observations of
solar eclipses, when high angular resolution at least in one coordinate was
achieved, did not answer these questions. The project was aimed at achieving an
angular resolution an order of magnitude higher than existing radioheliographs.
On this basis, we hoped for a detailed study of the development of events in
the corona at the background of the solar disk, for a possibility of improving
the scientific framework of flare prediction, as well as expecting to come
nearer to the study of the mechanism of development of flares and accompanying
events. It must be remarked that neither experience nor adequate financial and
technological means were available to us. For that reason, we had to develop
the project phase by phase, submit it to official expert examination and carry
out the prototype testing of design solutions until, in the 1970s, we were able
to embark on the construction of the instrument that was named the Siberian
Solar Radio Telescope (SSRT) [1, 2].
The initial instrumentation
enabled us to record only the most powerful manifestations of solar activity:
active regions, and flares. The lack of the necessary computer and receiver
technologies dictated the particular technique of formation of the beam and the
principle of operation of the SSRT. Progress was achieved by resolving the
problems of phasing the 128-element equidistant antenna arrays of long
electrical length (1.2x104 wavelengths), synchronous tracking of the
Sun throughout the daytime in climatic conditions of Siberia, recording the
radio brightness distribution of the solar corona, generating solar radio
images, and automating the operation and controlling all systems of the
territorially distributed SSRT complex. The successful phasing of such
multi-element antenna arrays added in creating, in 1992, the 17 GHz radioheliograph at Nobeyama Observatory
(Japan). The creation of the SSRT signified the advent in Russia of systematic
radioheliography and a meaningful breakthrough in solar radio astronomy. In
addition to the SSRT, the ISTP operates another two large astrophysical
observatories (the high-altitude observatory in the Sayan mountains, and the
observatory on Lake Baikal’s shore) for solar research in the optical range
[3]. The infrared telescope is under development; it is designed for solar
corona observation in the light of the line of He10830 A. Together with the SSRT,
they constitute a large astrophysical complex in East Siberia. The ISTP enjoys
one of the leading scientific schools of Russia in the field of research on solar activity and
solar-terrestrial connections; a wealth of experience on scientific instrument
making has been accumulated.
"The SSRT is a
crossed..."
Slide 5
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The process of mastering the SSRT has been
accompanied by an expansion of the scientific interests and a change of the
requirements to its characteristics. The advent of new technologies and
instrumentation made it possible to embark on the modernization of the SSRT
systems. The use of SHF amplifiers with a noise temperature of 50 degrees
allowed the SSRT sensitivity to be improved considerably, enabling the
recording and study of low-contrast features in the solar corona: coronal
holes, filament, and bright coronal points. The receiving-recording system is
being improved through the use of acoustooptic facilities. The methodology of
improving the solar corona radio image quality is under development. It has
been possible to achieve a spatial and temporal resolution of up to 15 sec of
arc and up to 14 ms, respectively.
The relatively high angular and,
especially, temporal resolution of the SSRT, together with the adequate
sensitivity, made it possible to considerably extend our research to almost all
forms of solar activity: new models were proposed (and the old models refined)
for active regions, flares, formation and acceleration of energetic particle
fluxes, coronal mass ejections, and coronal holes. First and foremost the
spatial-temporal characteristics of the origination and development of active
regions were studied. A detailed study was made of the phenomenon of the sign
reversal of the circular polarization of emission from the active region during
its solar disk passage, a number of new flare buildup signatures were
identified, an effective criterion of flare ‘protonicity’ from the character of
emission polarization distribution of the active region was developed, we
studied the properties and
suggested some likely
generation mechanisms for subsecond impulses of microwave emission during
flares and investigated the spatial structures of coronal holes associated with
their atmospheric heating characteristics [4]. The research efforts are carried
out in collaboration with observatories of Japan, China, Europe and the USA
using data obtained at ground-based and orbital observatories in all ranges of
solar emission.
However, two factors: the obsolescence
of the SSRT systems and the need to switch over to advanced diagnostics of
events in the Sun’s atmosphere which call for substantial improvement of the
speed for obtaining radio images, a simultaneous recording of the processes
occurring under different physical conditions, or a three-dimensional picture
of their development - led us in 1997 to the decision to create - on the basis
of modernizing the SSRT - a new-generation instrument, the multiwave
radioheliograph (MVRH) [5-7]. That decision is in full accord with the tendency
established in the 1990s in radioheliography (introduction of a second
frequency at NRH, development of OVRO, the proposal on the development and
construction in the USA of FASR at ~0.3-30 GHz
and LOFAR at 15-150 MHz , the decimetric array in Brazil at 1.2-1.7, 2.7
and 5.0 GHz, and Chinese Space Solar
telescope (SST), the radioheliograph at 1-30 MHz with high speed and resolution). The implementation of these
projects involves overcoming very challenging technical problems and requires
considerable funds. With their creations, scientists will have instruments at
their disposal, which would meet - for many years ahead - all conceivable needs
of solar physics and solar-terrestrial connections. They will revolutionize the
space weather prediction problem.
We are well aware of the expediency of
creating the new instrument meeting all demands of the near future. Therefore,
we fully support the ideas behind the creation of the above-mentioned radio
telescopes. Considering the realistic financial conditions in Russia, the ISTP
is working on two versions of SSRT conversion to MVRH which differ by the
speed, the methods of frequency conversion, collection of signals from the
antennas, and by the rate of obtaining radio images (in the modes of frequency
scanning and aperture synthesis). They show that in Russia it is possible to
create - with moderate expenses - a multiwave radioheliograph in the frequency
range 2-10 GHz. This instrument cannot
compete with FASR as regards the number of frequencies and spatial resolution
but will provide the necessary data for successful investigations in the field
of highly important problems in solar physics, including the space weather
prediction problem. The difference of the longitudinal location of the SSRT
(MWRH in the future) and FASR will make it possible to carry out mutually
complementary observations of the Sun on a 24-hour basis. The basic expenses
incurred by the implementation of the ISTP project reduce virtually to reequipment
of the SSRT by additional instrumentation; the antenna system, the
receiving-recording complex, the automation system, all civil engineering part
and infrastructure of the SSRT complex will be used in full measure.
Alterations may apply to the method and, hence, the system of signal
collection. Substantially smaller expenses will be required for the replacement
of the obsolescent CAMAC-modules (by modern microprocessors), cables, as well
as for the overhaul of the waveguide tunnel (water proofing, protection
devices). MWRH will be accessible to all interested observatories.
Scientific objectives of MWRH
1. Magnetography
of the corona - determination of the structure and strength of magnetic fields.
The effectiveness of magnetic field measurements in the active region corona
was demonstrated by RATAN and VLA observations, with limitations in spatial
resolutions and the field of view, respectively. MWRH would provide
measurements of the field at a number of levels in the chromosphere and corona
(estimations of the magnetic field in the chromosphere from the Zeeman effect
are made difficult by the structure of spectral lines). Angular resolution
varies linearly with frequency. Therefore, even in the case of a discrete set
of frequencies, MWRH can provide contours of field levels at the base of the
corona by assuming the emission from the 3rd gyrolevel B = 120 f (GHz). The coincidence of the SSRT and NRH
observing intervals brings the number of frequencies to eight. In relatively
weak fields, information about the magnitude of the magnetic field along the
line of sight is furnished by the degree of polarization. Investigation of
oscillatory processes at different frequencies (levels in the solar atmosphere)
is also associated with this problem.
2. Solar flares. Radio methods are no less
sensitive to observations of high-energy electrons than X-ray methods. Through
the use of several frequencies it will be possible to determine the spectral
index of emitting electrons, and the picture of the polarization - the
direction of magnetic fields. In many cases it is possible to observe weaker
structural elements and understand the topology of flare loops. Determination
of the magnitudes of magnetic fields in the flaring region - the most important
parameter for estimating the energy release. Observation of the
shortest-duration manifestations of solar activity associated with plasma
mechanisms of generations. In the study of flares it is also planned to use
one-dimensional observations with high temp[oral resolution.
3. Coronal
mass ejections. As demonstrated by experience of investigating the CME that
occurred on September 4, 2000, radio mapping provides essentially new
information about the origin of coronal mass ejections. The MWRH spectral range
make sit possible to investigate the process of CME development from the lower
corona to altitudes on the order of one solar radius (at the background of the
solar disk and in the height range inaccessible to observations in the H-alpha
line, SOHO coronographs, and to m-radioheliographs). Simultaneous observations
of all Sun in microwave emission will make it possible to study the association
of CMEs with other forms of solar activity: flares, shock waves, and filament
eruption.
4. Structures inside coronal holes, distribution
of plasma parameters in holes with the height.
5. Bright
coronal points - local energy release in the corona. They are observed at the
SSRT and NRH simultaneously. The brightness temperature ratio is indicative of
the bremsstrahlung mechanism of emission. Nevertheless, two frequencies are
insufficient for identifying the plasma parameters.
6. Applications.
Short-term prediction of geoeffective solar flares, base don a number of
signatures (polarization structure depending on the structure of the
photospheric magnetic field and on the active region location on the solar
disk, evolution of the microwave emission flux, etc.). Recording of CMEs.
Diagnostics of solar flare parameters. Alerts within the space weather program.
Education of young scientists with the new instrument.
The solution of the above-mentioned
problems substantially alters and enhance the requirements for new solar radio
telescopes. The MWRH project provides
for the attainment of a time resolution on the order of 1 s, and the
sensitivity and dynamic range will be sufficient for recording all forms of
solar activity, the angular resolution can be improved using remote antennas
(such as the antenna 32 m in diameter that is already under construction near
the SSRT for the Russian RSDB “Quasar” system).
With the frequency scanning of the Sun
preserved, it is intended to equip each antenna with a multiwave feeder and a
system of synthesizers to covert the signal frequency at the new frequencies to
the SSRT’s working frequency in order to
make use of the existing wideband system of signal collection, and to
temporally separate the recording of data at different frequencies [5-7] (Fig.
5). Elements from this version are already being worked out by co-participants.
However, this version does not provide radio images with the necessary temporal
resolution (on the order of 1 s). Already at the present time the SSRT
observations are impossible to use in cooperative programs such as HIGH CADENCE
IMAGING CAMPAIGN: MEDOC. Therefore, design solutions are under development for
switching over from many-frequency scanning to aperture synthesis. Preliminary
results show that this approach is realistic at present, as there is no need to
develop an expensive correlator, and with the present level of computer
technology, its function can be performed by a sufficiently powerful processor.
In this case it will be possible to map a full solar disk at intervals of about
1 s. Added expenses will be incurred by the use of fiber-optic communication
lines via antennas, switching elements, and by the purchase of the
processor.
Consequently, the use
of parallel aperture synthesis is more promising because to solve the
above-mentioned problems requires obtaining solar radio images at different
wave lengths with sufficiently high temporal resolution. It is obvious that
this can be realized only through the use of parallel aperture synthesis.
Slide 17
To do this, it is necessary to equip the SSRT
antenna elements with multiwave convertor modules (MCM). Each MCM will comprise
the polarization switch, the low-noise amplifier, the frequency converter with
the synthesizer as the heterodyne, the attenuator, the phase shifter, and the
microprocessor. It is admissible to use six wavelengths in the frequency range
from 2 GHz to 10 GHz (2340, 3100, 4340, 5730, 7815 and 0300 MHz). MCM converts signals of all waves received
by the antenna, to an intermediate frequency. Synthesizers at all antennas are
synchronized by the phase-stable reference signal. Signals at the intermediate
frequency are fed to the working room for a correlation processing.
An important characteristic of
MWRH would be the simultaneous obtaining of the spatial spectrum at different
wavelengths. To accomplish this, it is possible to use the redundancy of the
SSRT antenna system. Based on the objective of flare
and coronal mass ejection observation, the changes in spatial structures of
our interest are occurring in the region of high spatial frequencies. To record
them simultaneously, it is sufficient to fill the edges of the SSRT array with
antennas operating at different frequencies (Fig. 6). For measuring coronal
magnetic fields, the instrument will operate in the mode of sequential use of
working wavelengths (100...500 ms for each of the six working wavelengths). For
observing a quiet Sun, active regions, filaments, and coronal holes, use will
be made of the redundancy of the SSRT antenna system to simultaneously
obtaining spatial spectra at different wavelengths. Thus we expect to obtain a
flexible instrument for performing different tasks simultaneously.
It is intended to use the mode of sequential
obtaining of images at different frequencies in order to study coronal magnetic
fields, in addressing problems of predicting solar activity, and in
investigating low-contrast structures such as coronal holes and filaments.
Coronal mass ejections are commonly characterized by the angular size as large
as several tens of min of arc. Therefore, it is more appropriate to investigate
such phenomena in the mode of sequential obtaining full solar images at
different frequencies. Observations of ejections in the mode of simultaneous
obtaining a full solar image are appropriate only when accompanied by fast
occurring processes. For investigating the dynamics of solar activity (flares
and, possibly, coronal mass ejections), it is intended to use the mode of
simultaneous obtaining of a full solar image at 5.7 GHz frequency and high spatial harmonics of
corresponding images at the other wavelengths. A tentative configuration of antennas
for this mode is illustrated in Fig. 6. The field of view for frequencies above
5.7 GHz in this case will be reduced to
a few min of arc. This should not have a substantial influence on the
observations of flares as a consequence of their small angular size. However,
in observations of coronal mass ejections, such a limitation could have a
serious influence.
It should be noted that the
question as to the selection of the antenna configuration for simultaneous
obtaining of images at different frequencies is open. It seems most likely that
it will be answered in the process of observations. For this it is important
that the whole instrument has a sufficient flexibility. Such a flexibility is
ensured by equipping each antenna with a controlled multiwave receiver and by
the control of the process of calculating cross-correlation functions of
signals received from antennas.
Slide 20
Key issues of the MWRH project: the number of
antenna elements and the configuration of using them at the new frequencies,
frequency-agile feeders, versions of collection of signals from antennas,
heterodynes of frequency conversion 1 and 2, fiber-optic lines to supply the
heterodyne signal to antennas, separation and digitizing data at all
frequencies, data preprocessing and storage, SolarSoft, system analysis, and
matching of all subsystems. Cooperation, exchange of experience or sharing of
labor with relevant teams of the FASR project are possible and expedient in the
process of working out these issues.
State
of affairs. There is well-established cooperation of manufacturers of the
necessary additional equipment. Control systems and systems for controlling
over antennas, phase shifters and synthesizers are under development using the
state-of-the-art designs. New acoustooptic receivers are being produced, which
permit, already in the year 2002, recording two-dimensional images every 2-3
minutes simultaneously with one-dimensional scans from both beams, with a
resolution of 14 ms. Receivers, amplifiers and synthesizers for 6 frequencies
are under development. The technology for building multiwave feeders is being
worked out. Thus, with relatively low expenses (of about 15 million rubles), in
a period of two-three years it is possible to obtain a qualitatively new instrument
which outperforms the existing solar radio telescopes for the set of their
characteristics: the two-dimensional mode of operation with high spatial
resolution at six wavelengths, the possibility of observations throughout the
daytime, the possibility of carrying out patrol of fast processes on the full
disk with high temporal and angular resolution.
Optimistic hopes for the project
implementation plan:
Completion of working out the engineering issues 2002
Completion of prototype testing of design solutions 2003
Drawing out of the necessary documentation 2002-2003
Solving the problem of funding the project implementation 2002-2003
Project implementation 2003-2005
SUMMARY
1
An important characteristic of MWRH would be the simultaneous obtaining
of the spatial spectrum at different wavelengths. Obtaining radio images of the
solar corona during the daytime by recording all spatial scales is possible
through the implementation of adaptive multiwave approach. The essence of the
method is as follows. All SSRT antennas will be equipped with multiwave
modules. The adaptive multiwave mode make sit possible to realize a redundancy
of the SSRT antenna array. For calibrations and for observations of slowly
varying structures, it is intended to obtain solar radio images consecutively
at different wavelengths. Specifically, either all SSRT antennas or one and the
same optimum configuration will be used for each wavelength. Thus it is intended
to obtain a quality image of all Sun at six frequencies. The only limitation
will be the overlay of noon images at frequencies higher than the SSRT design
frequency, 5.7 GHz. This will be caused
by the mismatch of the lowest spatial frequency to the angular size of the Sun
for these frequencies. The use of all SSRT antennas in synthesizing the image
make sit possible to obtain a highest-quality image but increases substantially
(several times) the amount of information. Therefore, the selection of the
particular configuration in this case will be influenced not only by the
physical expediency but also by the overall performance of the system.
SUMMARY
2
1. The relatively high angular and, especially,
temporal resolution of the SSRT, together with the adequate sensitivity, made
it possible to considerably extend our research to almost all forms of solar activity.
2. However, two factors: the obsolescence of the
SSRT systems and the need to switch over to advanced diagnostics of events in
the Sun’s atmosphere which call for substantial improvement of the speed for
obtaining radio images, a simultaneous recording of the processes occurring
under different physical conditions, or a three-dimensional picture of their
development - led us in 1997 to the decision to create - on the basis of
modernizing the SSRT - a new-generation instrument, the multiwave
radioheliograph (MVRH).
3. We are well aware of the expediency of
creating the new instrument meeting all demands of the near future. Therefore,
we fully support the ideas behind the creation of the FASR and other new radio
telescopes. Considering the realistic financial conditions in Russia, the ISTP
is working on two versions of SSRT conversion to MVRH which differ by the
speed, the methods of frequency conversion, collection of signals from the
antennas, and by the rate of obtaining radio images (in the modes of frequency
scanning and aperture synthesis). They show that in Russia it is possible to
create - with moderate expenses - a multiwave radioheliograph in the frequency
range 2-10 GHz.
4.
The difference of the longitudinal location of the SSRT (MWRH in the future) and FASR will make it possible to
carry out mutually complementary observations of the Sun on a 24-hour basis.
5. Scientific
objectives of MWRH: Magnetography of the corona, Solar flares, CME, Structures
inside coronal holes, Bright coronal points, Applications.
6.
The solution of the above-mentioned problems substantially alters and enhance
the requirements for new solar radio telescopes. The MWRH project provides for the attainment of a time resolution
on the order of 1 s, and the sensitivity and dynamic range will be sufficient
for recording all forms of solar activity, the angular resolution can be
improved using remote antennas (such as the antenna 32 m in diameter that is
already under construction near the SSRT for the Russian RSDB “Quasar”
system).
7. Consequently, the use of parallel aperture
synthesis is more promising because to solve the above-mentioned problems
requires obtaining solar radio images at different wave lengths with
sufficiently high temporal resolution. It is obvious that this can be realized
only through the use of parallel aperture synthesis.
8.
Key issues of the MWRH project: the number of antenna elements and the
configuration of using them at the new frequencies, frequency-agile feeders,
versions of collection of signals from antennas, heterodynes of frequency
conversion 1 and 2, fiber-optic lines to supply the heterodyne signal to
antennas, separation and digitizing data at all frequencies, data preprocessing
and storage, SolarSoft, system analysis, and matching of all subsystems.
Cooperation, exchange of experience or sharing of labor with relevant teams of
the FASR project are possible and expedient in the process of working out these
issues.
9. An important characteristic of MWRH would be the
simultaneous obtaining of the spatial spectrum at different wavelengths. To
accomplish this, it is possible to use the redundancy of the SSRT antenna
system. We expect to obtain a flexible instrument for performing different
tasks simultaneously.
10. MWRH will be accessible to all interested observatories.
We greatly appreciate the support of the work
from the Siberian Branch of the Russian Academy of Sciences (SB RAS), the
Ministry of Industry and Science of the RF (Unique facilities: 01-27), the RFBR
(00-02-16456, 00-02-16819, 00-15-96710, 01-02-162900 and INTAS
(IR-1088).
REFERENCES
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Krissoinel B.B., Putilov V.A. and Potapov N.N.. The Siberian Solar Radio
Telescope: parameters and principle of operation, objectives and results of
first observations of active regions and flares. Astrophysics and Space
Science, 119(1986), 1-4.
2. Smolkov G.Ya., Treskov T.A., Krissinel B.B., Miller
V.G., Grechnev V.V., and Konovalov S.N. The Siberian Solar Radio telescope. In:
Regional
Monitoring of the Atmosphere”, pt.
3. Unique Measuring Complexes.
Novosibirsk: Nauka, Izd-vo SO RAN,
1998, Ch. 3, pp.85-149.
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V.P.Maksimov, A.M.Uralov and V.G.Zandanov. Some researches results from the
SSRT. Poster for the Workshop “Solar Radiophysics with the FASR” (May
23-25’2002, Green Bank, West Virginia).
5. Zandanov V., Altyntsev A. and Lesovoi S.
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Kiyosato). Abstract book. NRO/NAOJ, 1998,
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6. V.G.Zandanov, G.Ya.Smolkov, A.T.Altyntsev,
T.A.Treskov, B.B.Krissinel, S.V.Lesovoi, V.P.Maksimov. On development of SSRT. Wayfang Symposium (July’1999,
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7. Smolkov G.Ya., Zandanov V.G., Altyntsev A.T.
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Thank You