The Southern Hemisphere VLBI Experiment (SHEVE) program is aimed at producing high-resolution images of southern radio sources. The radio telescopes of the present SHEVE array are described below and some recent results presented.

The Sydney University Stellar Interferometer has been designed and constructed as a two aperture, single r o, long baseline, optical interferometer with wavefront-tilt compensation and dynamic optical path length compensation. Initially it will operate in the blue part of the visual spectrum but provision has been made for the addition of an additional beam-combining system for a second spectral band. The rationale behind the choice of instrumental parameters, the potential developments which have been taken into account in its construction, and the current status of SUSI are outlined.

One of the observing modes available with the ESO Very Large Telescope will be coherent combination of the light received by up to four 8 m unit telescopes and several 1.8 m auxiliary telescopes. The location of the main telescopes is fixed, while auxiliary telescopes can be moved among some 30 observing stations. The locations of these stations were chosen to augment the (u, v) coverage of the unit telescopes as well as to function as an independent interferometric array.

The 8 m telescopes will be equipped with adaptive optics to correct for seeing-induced wavefront aberrations. This wavefront correction will be complete at near-infrared wavelengths, giving the interferometer very high sensitivity in this spectral regime. This paper gives a brief description of the VLT Interferometer and an update on its status.

The Naval Research Laboratory and the US Naval Observatory are building a phase tracking optical interferometer for high resolution imaging and astrometry. This instrument will be a six element interferometer capable of true imaging using interferometric amplitudes and closure phases. This talk will describe the instrument, with an emphasis on those aspects of the array related to high resolution imaging. The status of the project will be presented. First light is planned for October 1993, with 6 element imaging beginning in 1994.

The purpose of this paper is to describe the operation of GI2T, the visible Michelson stellar interferometer with two 1.5 m apertures, as well as a presentation of its desired evolution.

The Cambridge Optical Aperture Synthesis Telescope (COAST) [1] will be the first instrument of its kind to exploit the techniques of aperture synthesis and closure phase to produce very high resolution (one milliarcsecond) optical images. The instrument will consist of four identical independent mobile 40 cm telescopes, and an optical building incorporating the path compensators and the fringe and acquisition and auto-guider detector systems. The present status is; there are three operational telescopes on site with two fully functional path compensator trolleys, an acquisition and auto-guider system capable of controlling up to four telescopes, correlator and a fringe detector system.

We propose an optimized design for the redeployment of the Multiple Mirror Telescope (MMT) primary optics as a 25 m Adaptive Steerable Imaging Array (ASIA) providing direct focal plane image formation. The design incorporates concepts of active telescope alignment and adaptive optics proven in the existing MMT. Basing predictions on contemporary radio telescope mount technology, 45 m to 100 m optical baselines may be practical.

CIROI (China InfraRed Optical Interferometry) Project would be probably divided into three stages: prototype, moderate aperture, and large aperture. The prototype with two collection apertures of 10 cm and baseline of 12 m for first testing stage is being manufactured.

The USNO Astrometric Interferometer (USNOAI; a subarray of the Navy Prototype Optical Interferometer at Lowell Observatory) is presently under construction and expected to begin limited operations within a year. The main goal of the USNOAI observations is to provide a northern hemisphere catalog of several thousand stars with positions known to a few mas. In order to meet this requirement, a baseline laser metrology system must be employed to measure the three-dimensional motions of the baselines with an accuracy better than ~ 0.1 μm. The metrology scheme, as presently conceived, represents the largest and most complex high-resolution laser metrology system ever attempted.

The beam combiner for the Big Optical Array will eventually combine 6 beams. Initially it will use the 3 way beam combiner shown in Figure 1. This combiner is assembled on a 4′x7′ super-invar breadboard. Simultaneous white light fringes have been detected on all three baselines in the laboratory. This paper describes this beam combiner and the design decisions upon which it is based.

The SUSI control system is a distributed real-time system currently consisting of 17 processors. A custom real-time operating system and network protocols ensure synchronous operation of servo loops across multiple processors.

We present a description of the pathlength compensation system used in the Sydney University Stellar Interferometer, and report on the method of fringe tracking that is being implemented. The components of this system are discussed, including the PAPA camera used to detect chromatic fringes, the fringe tracking servo, the delay line and its control.

In an optical interferometer, the delay lines compensate the optical path difference between the different arms of the interferometer, so that the interference patterns, which contain the information, can be observed. Thanks to the phase closure technics, the phase information can be extracted, despite the random phase shifts introduced by the atmospheric turbulence. As we used the redundant spacing calibration to reconstruct an image, the telescopes of the interferometer have to be arranged according to a given iterative procedure. The advantage of this technics is to enable the reconstruction of an image without any a priori knowledge on the object. But this implies constraints on the configurations of the telescopes array, and therefore on the offsets and on the kinematics of the delay lines. Their motion have been studied to define the future layout of the 3 telescopes optical interferometer of the Calern's Observatory (CHARON III project) and also to define the operational procedure.

The Micro-Precision Interferometer Testbed is essentially a space-based Michelson interferometer suspended in a ground-based laboratory. The purpose of the testbed is to serve as a proving ground for technologies needed for future space-based missions requiring low-vibration environments. A layered control architecture, utilizing isolation, structural control, and active optical control technologies, allows the system to achieve its vibration attenuation goals.

This paper focuses primarily on the interferometer instrument design for the testbed and the systems-level tradeoffs between the instrument and other systems due to the fact that the interferometer is on a large, lightly damped, flexible structure rather than on the ground. The testbed is designed to be a fully functioning interferometer spacecraft and makes use of flight-like hardware where possible, including an external star simulator, an attitude control system, fringe detection and tracking systems, delay lines, pointing control, laser metrology systems, and computers and electronic subsystems. The engineering decisions that led to the current instrument configuration are presented and explained.

A new method to reconstruct the phase of bidimensional interferograms, obtained through pupil-plane interferometry is presented. We compute the average complex phasor components of the cross-spectrum on a data set to reconstruct the original unperturbed phase. We present preliminary results on simulated images which visibility phases are distorted using a model of atmospheric perturbed wavefronts.

If flux density variability is intrinsic to extragalactic sources, then the shortest time scale of the variability yields an extremely high angular resolution. There is, however, good evidence that some of the variability is due to refractive scintillation in our galaxy's interstellar plasma turbulence. The effect, initially discovered at low radio frequencies, is here shown to extend into the GHz band, which, up to now, has been assumed to display only the intrinsic variability. We conclude that further study in both the intermediate and high frequency bands needed to separate the intrinsic and extrinsic components of variability.

Lucy's algorithm is applied to iterative blind deconvolution method. This new approach enables to reconstruct a greatly extended object from one speckle frame and to reinforce image domain constraints. A greatly extended object makes speckle images flow over detecting surface. Lucy's algorithm is accommodated to handle such an image and built into iterative blind deconvolution methods. Computer simulation and observational data analyses are conducted and the effectiveness of the proposed methods are exemplified.

A technique for reconstructing diffraction-limited image of an object from speckle images without reference star is applied to both simulated and real data. The object spectrum is estimated by blind deconvolution using the power spectrum of the speckle images and the phase is restored from the bispectrum.

We have run a number of simulations investigating the limitations of noiseless point spread deconvolution with the VLA. On-source errors of more than .01 and off-source dynamic ranges of less than 15,000 were found for some parameters typical of high precision observations. Deconvolution errors were not confined to the support of the source, and limit the dynamic range in at least one VLA observation.

The problem of image reconstruction from incomplete and noisy complex Fourier spectrum is considered. The maximum entropy method (MEM) is of great interest as the most effective nonlinear reconstruction method having superresolution effect. Because objects of radio astronomical observations are incoherent radio sources described by real non-negative distributions, application of the classical MEM is quite reasonable. But it is established that the MEM gives acceptable reconstruction quality mostly in the case of point-like sources and in general it does not ensure satisfactory reconstruction of continous, graytone objects, which can considerably restrict applications of the MEM in astronomy. The generalized maximum entropy method (GMEM) was originally proposed for reconstruction of distributions described by complex functions (Bajkova, 1992) and was considered as having the same properties of the classical MEM. More careful analysis of the GMEM and classical MEM for real non-negative objects allowed to establish that the GMEM ensures much more exact reconstruction, especially in the case of continous objects. Explanation and demonstration of this interesting and very important phenomenon is the purpose of the present paper.