The First PHotoelectric Astrolabe (PHA I) of China was installed at Shaanxi Obs. in 1971 and came into use later. PHA I has been operating automatically since 1986. Now it is being revised by using a single image with autocollimation, equipped with photon counting system and a tracking diaphragm with a small window to follow the star in zenith direction, which would cut off the most light of the night sky. With all these three approaches, PHA I could improve its limiting magnitude from mag. 6 to mag. 11 or even fainter.

The IAU Working group on Earth rotation in the Hipparcos reference frame, set up by IAU Commission 19 in 1988, is presently preparing the algorithms and collecting the data obtained by optical astrometry since the beginning of the century. The main idea is to use the observations of individual stars rather than group results, all recalculated in the unique system of astronomical constants and algorithms. The final solution will be referred to the celestial reference frame realized by the Hipparcos star catalog presently under preparation. All known geophysical influences (as e.g. solid and oceanic Earth tides or plate tectonic movements) will be included into the model. In addition to traditional Earth rotation parameters (polar motion, universal time), also the pole offset components in the celestial reference frame will be solved for, as well as other relevant parameters (systematic seasonal deviations of the individual stations, instrumental constants etc.). The present status of the solution and the time evolution of its expected accuracy are described.

Past optical astrometric observations are to be re-reduced in order to get a new evaluation of the Earth Orientation Parameters in the more accurate Hipparcos reference frame. Among the selected instruments is the Paris astrolabe, considered here. In this Paper, through multivariate statistical procedures, we deal with the preliminary step of the new evaluation which consists in detection and separation of sources of significant inconsistency and outstanding errors in the Paris reductions so far performed. The analysis is performed over two test periods — one per instrumental setting-that are compared in particular in terms of observer effects, magnitude, colour and sidereal time effects. The Paper also gives a synthetic overview on the statistical methods we used to obtain the main results so that they can be applied to other astrometric data.

The nearby stars constitute the statistically most complete and therefore most representative sample of stars in our Galaxy. Only this sample allows a direct investigation of luminosity function and kinematics of low-mass stars.

A study of the Third Catalogue of Nearby Stars reveals a considerable increase — not only in quantity but also in quality — in our knowledge of the immediate solar neighbourhood, and reflects very nicely the progress achieved during the last decades — especially in astrometry and photometry. Expectations for the near future (HIPPARCOS) and desiderata for further astrometric and photometric work will be discussed.

A algorithm for digital image centering with the maximum likelihood method is described. The astrometric accuracy of this algorithm is similar to the two-dimensional Gaussian fitting. For saturated images, this algorithm is better than the Gaussian fitting. With the maximum likelihood method, some systematic effect, such as coma and magnitude equation, can be reduced significantly.

Information on the recent results of the tests of the mirror, measuring equipments and computer control is given. The astrometrical capabilities of the MAHIS are considered.

After the automation of the Pulkovo HMC two catalogs of Positions of 1081 Stars from FK5B, FK4S, FKFS and RRS were observed. Every star was observed more than three times during the period from March 1988 to May 1990. The internal error of a single observation of FK5 stars was estimated as 0.S015(Sec-Z)0.6, 0″.16 (Sec-Z)0.9 in α and δ. A comparison of the declination of FK5B Stars observed with HMC with those of Bordeaux 86, CAMC 86 and PMC 86÷88 shows the Δδδ differences of the order of 0″.1 in the declination zone 40°÷60°.

A principle of a CCD-Tracking System for wide-field astrographs is proposed. This system can be used for precise relative positioning of fixed and moving, bright and very faint optical objects with respect to reference stars. Estimates of the positioning accuracy are given for objects of the 10÷20th magnitudes when observing with the K. Zeiss wide-field astrographs.

A multi-access automatic circle reading system for Chinese-Danish Meridian Telescope has been developed in CSAO. It consists of circle scanners and photon-electric counters. The method, in using TP-801B Single board computer as main controller for the system, is proved to be successful. It has advantages with low cost, high quality and easy operation. One CTC chip, three PIO chips and relational circuts are all of I/O interface. These programable chips are provided in the board or expanded by designer.

The declinations of stars are determined by the circle micrometers on the meridian circle. The determined accuracy of declinations depends on the systematic accuracy of the micrometers. The DCMT (Danish Chinese Meridian Telescope) adopts photoelectric scanning micrometers as the circle reading system. It contains 6 micrometers forming 3 pairs to measure the circle posistion simultaneously. The repeatability of the circle reading and systematic errors of micrometers are discussed in this paper.

The compilation of three years of observations by the improved photoelectric astrolabe of CERGA has provided a star catalogue with an internal precision of 0.03″ in right ascension and 0.04″ in declination for 47 stars and a similar precision for 82 other stars solved only for right ascension (Vigouroux et al., 1992). The classical group reduction was used. External comparisons with preliminary HIPPARCOS positions showed that these numbers represent the accuracy of the catalogue. However, many changes in the instrument and in the reduction procedures are contemplated that should bring new significant improvements in these results.

Shanghai Observatory has been the institute where astrometric observations are collected and treated after 1988.0, some tables are given here with which one may understand its recent situation.

Very-long-baseline Interferometry (VLBI) has opened for study a broad new spectrum of geophysical phenomena including: direct observation of the tectonic motions and deformations of the Earth's crustal plates, observations of unprecedented detail of the variations in the rotation of the Earth, and direct measurement of the elastic deformations of the Earth in response to tidal forces. These new measurements have placed significant constraints on models of the interior structure of the Earth; for example, measurements of the variations in the Earth's nutation have been shown to be particularly sensitive to the shape of the core-mantle boundary. The VLBI measurements will allow us to construct a global reference frame accurate at the centimeter level. Such a frame will be essential to studying long-term global changes, especially those changes related to sea-level variations as recorded by tide gauge measurements.

This paper presents several applications of a few hundred microarcsecond (μas) astrometric technique which has been developed and demonstrated using differential very long baseline interferometry (VLBI). A brief description of the technique along with several applications will be discussed below. This technique was developed for high-accuracy deep-space tracking, but the first application tracked an extragalactic radio source in a measurement of Jovian relativistic deflection. Current work includes making a state-of-the-art solar deflection measurement, and thus, an improved determination of the Parameterized Post Newtonian (PPN) gamma parameter. A number a future spacecraft tracking applications, described below, are also enabled by this technique.

Modern VLBI observations for both astronomy and geodesy continue to demand the utmost in sensitivity. Of the methods potentially available for increasing the sensitivity of continuum VLBI observations, increasing the recorded bandwidth is generally the most cost effective.

Over the past two years a broadly-supported program has been underway at Haystack Observatory to increase the sensitivity of the Mark IIIA VLBI system by more than a factor of 2. The result is an upgrade to the existing Mark IIIA data-acquisition system, dubbed Mark IV, which increases the maximum data rate to 1024 Mbits/sec, more than quadrupling the maximum data-rate of the Mark IIIA.

A new correlator, based on a new custom VLSI correlator chip is also being designed to support the 1 Gbit/sec data rates from the Mark IV data-acquisition-system. An international collaborative effort is being mounted to help defray the high costs of development.

Dual frequency Mark III VLBI observations acquired since 1979 by several geodetic and astrometric observing programs have been used to establish precise celestial and terrestrial reference frames. The program to establish a uniformly distributed celestial reference frame of ∼400 compact radio sources with optical counterparts was begun in 1987. Some 700 sources have been considered as part of this effort and a preliminary list of ∼400 has been observed. At present, 308 sources have formal 1σ errors less than 1 mas in right ascension and 308 have similar precision in declination. The astrometric results include some data acquired for geodetic purposes. The geodetic results using data to September, 1992 include the positions of 105 sites with formal 1σ horizontal errors generally less than 1 cm at 1992.6 and the velocities of 64 sites with formal 1σ horizontal errors generally better than 2 mm/yr.

The Deep Space Network (DSN) Radio Reference Frame consists of a catalog of angular positions for 281 extragalactic radio sources based on VLBI measurements made during the period from 1978 to 1992. A realistic assessment of the accuracy of these source position estimates must consider both modeled stochastic errors and systematic model deficiencies. Modeled stochastic errors include thermal noise (signal-to-noise ratio) and fluctuations in tropospheric refractivity due to the changing distribution of water vapor. These modeled errors result in a median formal position uncertainty of ≈0.3 milliarcseconds (mas). In particular, we examine the effect of changing the model for inter-observation correlations of water vapor fluctuations on estimated parameters. Next, a comparison of our radio source positions with independently determined positions is presented as evidence of systematic errors at ≤ 0.5 mas. We discuss several aspects of VLBI model accuracy focussing on tidal effects, antenna thermal expansion, pressure loading, source structure, precession and nutation. Prospects for reducing these errors are also discussed. We conclude by combining these estimates of modeled stochastic errors and systematic errors into an overall assessment of < 1.0 mas for the current accuracy of the DSN extragalactic radio frame.

We use the baseline variation rates, which are obtained by the VLBI measuring in the past years (1979. /-1991.1), to estimate the relative motions among Eurasian, Pacific and North American plates. A comparion with the geological-based models has been made. In order to strengthen the VLBI constraints on the Euler vectors, we estimate the velocities of unstable stations in addition to the Euler vectors.

Geodetic VLBI experiments are usually conducted at S/X dual bands. Some advantages can be gained at some higher frequency band and in particular at 22 GHz band (K band). We organized a geodetic VLBI experiment on the 16th of February 1991 between Kashima 34m antenna of the Communication Research Laboratory (CRL), in Japan and Medicina 32 m telescope of the Institute of antenna(IRA), in Italy. The phase calibrator was developed using a new “up-conversion” scheme for K band. Data relative to 212 observations of 40 sources were correlated and for 152 scans we obtained correlated amplitudes, delays and delay rates. The r.m.s. residuals have been found to be 100 ps for delays, and 74 fs/s for delay rates. The coherence loss of correlation amplitude becomes large at higher frequency band than 22GHz due to the atmospheric scintillation. The estimated method of the coherence loss was presented. The correlated flux densities at K band evaluated from them were found to be smaller than the ones at X band in general.

The Institute of Applied Astronomy of the Russian Academy of Sciences (IAA RAS) is constructing the VLBI complex “QUASAR” consisting of six antennas across the former USSR. The complex will be a dedicated instrument for space geodesy and radioastrometry. Three aspects of the “QUASAR” project will be discussed. First, the description of the project and its concept will be presented. Secondly, the current state and problems of constructing the network will be outlined. Finally, some information on the international cooperation will be given.