Geodetic VLBI experiment at 22GHz band
Yukio TAKAHASHI
Current geodetic VLBI experiments are conducted in S/X band. Improvements of
precision are desired in the geodetic VLBI. The geodetic VLBI in 22GHz is the one
of the solution to this demand, because of following reasons;
- (1) The observation bandwidth can be expanded easily. The precision of geodetic VLBI
is inversely proportional to the bandwidth.
- (2) Ionospheric delay in 22GHz band is smaller than one in X band. The ionospheric
delay will be corrected using GPS equipment. All video channels are used for only
22GHz band, so SNR can be improved
- (3) Tipping data of the same antenna will be obtained the water vapor data as WVR
(Water Vapor Radiometer).
- (4) The precision of delay rate becomes better since it is inversely proportional
to the observation frequency.
The geodetic VLBI needs the phase calibration (PCAL) data for each channel in the
observation band. CRL developed a new PCAL equipment in 22GHz band. At 16th February,
the geodetic VLBI experiment in 22GHz band was conducted between the Institute of
Radio Astronomy (Bologna, Italy) and CRL (Kashima, Japan). The purposes of the
experiment are
- (1) to check of the new PCAL equipment for 22GHz in the international geodetic VLBI
experiments,
- (2) to obtain the basic data of the radio sources and the baseline analysis.
In this experiment, 240 observations were conducted for 40 radio sources. We succeeded
in the experiments, band width synthesis and baseline analysis. The r.m.s. values
of delay and delay rate residuals were 183ps and 94fs/s respectively. The r.m.s.
values were almost the same as the r.m.s. value in standard geodetic VLBI experiments
in S/X band because we did not use wide band receiver this time and ionospheric delay
corrections. The information of the sources in 22GHz band, such as the correlation
flux and the resolution, were obtained on the long baseline (8000km). The relation
between the distance (z) and the correlation flux density. The new method to estimate
the coherence loss by the atmospheric scintillation is proposed. The data will be
useful for the future geodetic VLBI experiments in 22GHz band.
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