Earth Rotation Observation and other Current Topics
by Yukio TAKAHASHI
1. Status of Earth Rotation Observations
The regular VLBI experiments (IRIS-P) have been conducted every month for the
earth rotation observation. However, the high density head of the MarkIII type
data recorder in Kashima got a serious problem last year. It was repaired by
Haystack Radio Observatory, and Kashima started IRIS-P observation again since
January 1992. We will stock the high density head in the National Astronomical
Observatory.
We will participate in the intensive VLBI experiments this summer which are
proposed by USNO, because we have been making efforts to undertake such
intensive VLBI experiments since several years. The test experiment was already
conducted on March 10.
CRL and NAO discussed the possibility of observation in IRIS-P network by K-4
system and also with Mark-IIIa system in order to conduct the more frequent
observation (weekly) and intensive VLBI together with the other IRIS network and
NAVNET.
2. Other Toprcs
2.1 VLBI Experiments with the Syowa Station in Antarctica
VLBI terminals of Syowa Station were set up not permanently but temporarily in
the first experiment (1990). CRL provided technical suggestions to the National
Institute of Polar Research for the permanent VLBI system at Syowa Station, such
as H-Maser frequency standard, Receiver system, K-4 data acquisition terminal
and the check system at Syowa station.
2.2 Absolute Sea Level Monitoring by Space Geodetic Techniques
We have developed a transportable VLBI station for the absolute sea level
monitoring in cooperation with Geographical Survey Institute (GSI) under the
auspices of Environment Agency. The 2.4m antenna system, which is the smallest
for VLBI, was already developed with only X band receiver. If we observe the
Total Electron Content by GPS receiver such as TECMETER developed at CRL during
VLBI observation, we can reach almost the same precision as with the dual
frequency observation by increasing the number of observations. We will start
the mobile VLBI experiment this year.
2.3 Geodetic VLBI Experiment at 22GHz
A new type Phase Calibration equipment for 22GHz band was developed at CRL. And
it was applied for the geodetic VLBI experiment in the 22GHz band which was
conducted at 16th February in 1991, in cooperation with Institute of Radio
Astronomy in Bologna University (Italy). We obtained the fringes at 22GHz band
for a 8000km baseline using 40 quasars. And we made a baseline analysis.
We also estimated the coherence loss caused by the atmospheric scintillation
using a phase calibration signal. It is applicable for estimating the amplitude
of the radio sources. It implies the importance of the Phase Calibration signal
for the astronomy in 22GHz band.
2.4 Differential VLBI Technique
CRL and NAO are developing new differential VLBI technique using 34m and 26m
antenna in Kashima, and 45m and 6m in Nobeyama. The influence of the
instability of hardware and atmospheric scintillation can be canceled out more
precisely than the usual differential VLBI to change the antenna pair. The
precise source position will be also obtained, and the phase delay may be useful
to improve the precision of the geodetic VLBI. (See the following Figure)
