Brazilian Decimetric Array

Adv. SpaceRes. Vol. 25, No. 9, pp. 180~1812,200O 0 2OilOCOSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0273-l 177/00$20.~ + 0.00 www.elsevier.nlnoeate/asr zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA PII: SO273-1~77(~~591-8 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPON Pergamon BRAZILIAN DECIMETRIC ARRAY zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR H. S. Sawanti, K. R. SubramauianI*, E. Liidke2, J. H. A. Sobr& R. R. RosaI, W . D. Gonzalesr, and J. R. Cecatto’ G. Swarup3, F. C. R. Fernaudes’, 1Nuti~uZ zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA I~~~ t e f or Space Research - INPE, C.P. 515, ~~~~1-9~~ Sib Jose’ dos Barnes, SP, Brazil 2Department of Ph 1tics, Federal Univ. of Santa Maria, Santa Mwia, RS, Brazil 3 Tata Institute of findamentaf Reaseawh, Poona Univ. Campus, Ganeirhkhind, Pune, .#I1 007, India *On leave from Indii Institute of Astrophysics, Koramangala, Bangalore - 560 034, India ABSTRACT A radio heliograph operating in the frequency range of 1200-1700 M Hz is planned by INPE, Bra&, for investigationsof time evolution of active regions, which will lead to better understanding of the physics of the flares energy release and particle acceleration, in order to suggest better criteria for the prediction of solar &res, Coronal M ass Ejections (CM E), and solar terrestrial relations, such as noetic storms and radio blackouts. In the first phase, the Brazilian Deciietric Array (BDA) will be a T shaped array 256 m by 144 m, consisting of 26 parabolic dish antennas of 4 m diameter. This army will produce full disk images of the sun with a spatial resolution of 3 by 5 arc minutes at 1420 M Hz with a time resolution of zyxwvutsrqp 100 ms and sensitivity of N 10 Jy. In the second phase, in addition to the compact T array there will be 6 more 7 m diameter antennas on an East-W est baselineof 2560 m to obtain higher spatial resolution and better sensitivity. Thus, finally this radioheliographwill have wide field of view and couple of arcsec spatial resolution and high time resolution (100 ma). 0 2000 COSPAR.Published by Elsevier Science Ltd. INTRODUCTION Decimetric observations were carried out since 1960, however, for almost two decades they remained stagnant. SKYLAB soft X-rays observations (Star, 1980) suggested that acceleration of the particles most likely occurring near the region where the de&metric plasma emission is emitted. This renewed interest in the de&metric observations. Hiih time and spatial resolutions decimetric observations can significantly contribute to the understating of the physics of the flare energy release and particles acceleration. For investigation of decimetric solar radio emission many radio spectrographs are in operation, including the high sensitivity, high time and frequencyresolution digital spectrograph of INPE (Sawant et aZ., 1996). However,there is lack of informationon the location and size of the radio bursts at decimetric wavelengths. There are not many investigations of the regions from which de&metric radio bursts originate except very few observationsmade by VLA (Gopalswamy,1995). Thus, the data from the planned heliograph will also complementobservations made by Nobeyama Radio Heliograph (Niio et al., lQQ5),at 17 GHz, Narrcay Radio Heliograph (Radio hush group, 1993), at 100, 327 and 408 M Hz and Ga~ibid~~ Radio Heliograph ~Subr~~ et al., 19Q4) opiate zyxwvutsrqponmlkjihg in the frequencyrange of 40 - 156 M Hx, and thus will be part of a world wide network for ~nt~~~ monitoring of the solar radio emissionand allow us to study the evolution of active regions. ARRAY CONFIGURATION AND ANTENNA SYSTEM - PHASE I In the first phase, the BDA will make full disk images of the sun in the Stokes parameter I in contimmm with observing frequencytunable between 1200-1700 M Hz. The T compact array (256 m in EW direction and 144 m iu S direction) (Figure l), will be operating to obtain full disk solar images and will allow to produce images in a snap shot mode similarto the well knownsupersynthegisarchitecture proposed in early seventies (Thomspon et al., 1980), Clark Lake TPT array (Erickson et ul., 1982; Sawant et al., 1982, 1984; 1809 Ii. S. Sawant el zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG al zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLK zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM 1810 Kundu zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA et al., 1986).aud used in Giant Metmwave Radio Telescope (Swarup, 1990). The array will be located at Cachoeira Paul&a, Braail (44.7” W and 22.7* S). The primaryantennaelementused is a parabolic dish of 4 m diameterwith a dual polarisationfeed operating in the frequency range of 1200-1700Ml& at the prime focus which has the advantage that it can be nsed over the full frequency range of the ref&ctor. The effective collecting area of each autenna is - 7.5 m2 with an aperture efficiencyof 60 %. The reflectivesurface will be wire mesh. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM BRAZILIAN DECIMETRIC ARRAY (BDA) Fig. 1. Antenna location plan for the BrazilianDecimetric Array. The half power beamwidth of the reflector is - 3 deg at 1420 MHz. Each antenna will be supported by a equatorial mount. Tracking of all antennas will follow the intended sky position with an accuracy better thau 2 arc min. Each ant-a will be fitted with a 12 bit incrementalencoder with a non volatile memory, The drive system will track the sun for about f 4 hrs around local noon and will take care of the wind torques on the antat 80 km/h which is the maximum operational wind speed at antenna height at Cachoeira Paulista. FRONT END RECEIVER SYSTEM At the front end the RF signal from each antennawill be amplifiedby a low noise (1.2 dl3) tuned (1290-1700 MHz baud) amplifierand passed through a band pass tilter to eliminatethe image band. The RF amplifiers and baudpass filters will be kept in a temperature controlled enclosure to minim&e the phase and gain variations. The RF signal will be brought to the receiver box located at the base of the antenna by low loss cables. The receiver box will be buried at 1.5 m below the ground to keep the temperaturevariation minimum. The RF signal will be double converted into IF at 10 MHz with 2 Ml& bandwidth and further amplified by video amplifieras shown in Figure 2. The IF signal will be modulated using Walsh function and send to the receiver building using low loss RF cable. The IF signal will be split into sine and cosine components using quadraturehybrids in the receiver building. The local oscillator will be phase locked to a frequency standard and will employ modern phase locking techniques(Rhode, 1990) to compensate automaticallythe phase and frequency fluctuationsfrom the local oscillator electronics and due to temperature variation of the cables. M~t~~n~y observationswill be carriedout by varyingthe frequencyof the first LO. The IF signalwill be phasecoherentfor digitalcorrelation in single sideband one bit correlator which is sufficient for solar imaging. Programmableattenuators will keep the level of the signal within the range requimd for the correlator inputs. Calibration will be done using noise injected at the input of the receiversystem using noise diodes. 1811 Brazilian Decimetric Array zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM AT RJ Z SEX V FZ R BOX zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP Fig. 2. A schematicdiagram of the front end receiversystem. DIGITAL CORRELATOR SYSTEM To permit s~~~~~ rn~~rn~t of complex vibes function of 325 (n~n-l~/2 where n=26) interferometer baselinesbetween the various autenna groups, a 650 channel one bit digital correlator (Weinreb, 1963) system is planned which obtains the real and imaginary parts of the complex visibilities for each antenna pair in the array. The IF siguals will be quantized as 2 levels using zero cross detectors and over sampled at the rate of 10 MHs for fmer time delay resolution to reduce the coherence loss to less than 2 %. The digital delay also will make a prep fringe rotation to correct for the delays in the wavefront due to the earth - sun system. The neccxl&ary delays will be implementedunder the control of a computer with maximum value of ‘74 microseconds for EW antennas (for f 4 hour trackiug, 256 m baseline) and 34 miuosenconds for South arm (for rf: 45 degrees zenith angle coverage, 144 m baseline) in steps of 0.05 microseconds to reduce the coherence loss to less than 1.5 %. The correlator system will be built using custom built chips designed for Nobeyama radio heliograph (Nishio et al., 1995). Each corr&tor chip can multiply signalsfrom 4 antenuasand can give 8 real multiplicationsOne bit correlationresultsin the loss of amplitude information of measurementof fourier components. Therefore the s&ml strength iucludiug the receivernoise is measuredfor each antennaseparatelyand stored in the briifermemory along with correlator data every 100 ms. DATA ACQUISTION SYSTEM The m&er computer at the control building will be a SUN work station ULTRA 1 which will read the correlation visibiliti~ through a commercial VME - SCSI interface, apply prehminary corrections to the data by zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA a C+ + program written for UNLX/Solaris2.5. The interferometervisibiities will be then stored in an Hexabyte tape in an NRA0 Astronomical Image Processing Software (AIPS) readablestandard FITS format. The master ~mputer will also supply pointing tables to the slave ~rnpu~ at the antennasites for antennaand receiverdiagnosis. The fourier imaging to obtain the solar imageswill be done using procedures implementedin the AIPS software. Since the observed interferometervisibiitiea differ from the true visibilitiesdue to antenna based complex gain and correlator o&et errors, they have to be corrected by calibration. Since the BDA has enough reduudaucy,redundantcalibration will be used like Nobeyama (Nishio et al., 1995) and Gauribidauurradio heliographstSubr~~ et al., 1994) and Westerbork SyuthesisRadio Telescope (Barn+et al, 1973). H. S. Sawant el al. 1812 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML Speci8cationsof BDA system in phase I is given in Table 1. Table 1 . Specifmationsof BDA Phase I zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR ANTE~ AS 4m 3 deg at 1420 MHz 1200 - 1700 MHz 8hrs 90 deg Diameter Field of view T&king (maximum) Zenith angle coverage ARRAY Number of antennaa Total collecting area Baseline Spatial resolution Sensitivity(2 MHz BW, 100 ms integration) RECEIVER SYSTEM 1200 - 1700 MHz 2 MHz too ms Observing frequency IF B~dwidth Time resolution DIGITAL 26 N200m2 8mto24Om 3x5 arcmin at 1420 MHz N 10 Jy CORRELATOR Number of channels Number of bits SYSTEM 650 1 CONCLUSIONS The planned BrazilianDecimetric Array will be a powerful radioheliographin the southern hemispherefor investigationsof basic problems related to solar flares such as energy releaseand particle accelerationand CME for related space weather. ACKNOWLEDGEMENTS Thanks are due to Profs. K. Shibasakiand A~~~, Dr. H. Nakajima, Dr. M. Nishio, Dr. R. Ramesh and Dr. T. Watanabe for suggestionsleadii to improvementof the design of BDA. One of us, K. R. Subramaniau,is supported by CNPq under grant 3935&97/O. The participation of H. S. Sawantin the 32nd COSPAR ScientificAssembly was supported by FAPESP under grant 98/94282-g. REFERENCES Barrs, J. W. M., J. F. Van Der Bruggn,and J. L. Cassae, Pm. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG IEEE, 61, 1258 (1973). Erickson,W. C., M. 3. Mahoney, and K. Erb, ApJ S. Series, 60,493 (1982). Golly, N., ApJ, 435, 892 (1995). Kundu, M. R., T. E. Gergely, S. R. Kane, and H. S. Sawant, Sol. P&a., 103, 153 (1986). Nancay Radio Heliographgroup, Adu. Space &es., 13(9), 411 (1993). Nishio, M., H. Nakajima,and S. Enome, Xofi Symposium,pp. 19 (1995). Rhode, U. Digital Phase Lackeded Loops, Theory and Applicotion~, John - Wiley & sons (1990). Sawant,H. S., T. E. Gergely, and M. R. Kundu, Sol. P&s., 77, 249 (1982). Sawant,H. S., J. H. A. Sobral, F. C. R. Fernandes,J. R. Cecatto, W. R. G. Day, J. A. C. F. Neri, E. M. B. Alonso, and A. Moraes, Adv. Space Research,17(4/5), 385 (1996). Subramanian,K. 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