The concept of the Radio Schmidt Telescope is designed to fill a scientific requirement for a radio telescope which is very sensitive to diffuse, extended emission, but has much higher resolution than singleantenna telescopes. This telescope undertakes to utilize a new region of “parameter space” in the aperture synthesis technique. The emphasis of this article is on a process leading to the best implementation of the concept at reasonable cost while satisfying all the scientific objectives.

Four candidate imaging aperture synthesis concepts are described for possible emplacement on the Moon beginning in the next decade. These include an optical interferometer with 10 μarcsec resolution, a submillimeter array with 6 milliarcsec resolution, a Moon- Earth VLBI experiment, and a very low frequency interferometer in lunar orbit.

The time is ripe for planning an array with a collecting area of 1 km2 (14 times larger than Arecibo and 75 times larger than the VLA). In view of its major astronomical target I have dubbed this concept ‘The Hydrogen Array’, although 1μJy continuum sources will also be reliably detected. I present some initial thoughts about the issues involved.

We discuss the use of the moon as a passive reflector for radio interferometry experiments with baselines on the order of the radius of the orbit of the moon. Because of the extreme loss in the lunar interferometer path, only exceptionally strong point sources are candidates for this kind of interferometry. As the moon is far from an ideal reflector due to the irregular surface, the data processing necessary to optimize the fringe detectability is rather complicated. What we present here is a very brief summary of a paper describing the lunar interferometer in the Astrophysical Journal (Hagfors, Phillips and Belkora, 1990) and an experiment currently underway at Arecibo to test the lunar interferometer using Jupiter’s strong bursts at 25 MHz as a source. All references pertaining to the lunar interferometer are to be found in the Astrophysical Journal paper; this summary includes references concerning the test of the interferometer at Arecibo.

Presented here are the results of simulations of the effects of various errors on the imaging capabilities of the compact (72 m) configuration of a 39 element homogeneous millimeter array using the mosaic algorithm to image sources larger than the primary beam. Included in the errors investigated to date are systematic and random pointing errors, Gaussian receiver and atmospheric noise, and primary beam errors. Various methods of quantifying the quality of the reconstructed image are also discussed.

This is a continuation of earlier imaging studies for the MMA. Earlier work is confirmed, and the differences in imaging quality resulting from small and larger central antennas used for short-spacing information are investigated. An algorithm is presented which uses interferometer data to correct for an important component of central element pointing errors.

The proposed Fast All Sky Telescope (FAST) is an interferometer which is intended to monitor the northern four-fifths of the celestial sphere every two days at 8.1 GHz and daily at 2.7 GHz. The design goal is to have a rms sensitivity of 10 mJy/beam at both frequencies. The array is planned to comprise 20 3-meter diameter antennas with a maximum baseline of 0.7 km. FAST will provide a valuable database that may be used to study time variability in a sensitivity limited sample of radio sources. This will significantly impact on the understanding of active Galactic and extragalactic radio sources, as well as on the understanding of radio wave scattering in the interstellar medium.

We give here a brief report on the status of the IRAM Interferometer which is now in operation on Plateau de Bure.

Emphasis in the design of the Canadian Geophysical LBI (CGLBI) system has been placed on economy, operational efficiency, and performance in geophysical applications. Unique features of the system include the use of modified VHS recorders to store digitized astronomical data and the capability to track delay and fringe rotation during observation. A prototype system has been completed and tested at L-band using the ARO-DRAO interferometer baseline. The prototype system converts a single fixed 12 Mhz wide IF channel to baseband. Since delay resolution with this system is not sufficient for modern geophysical applications a frequency switching capability is being designed to synthesize a wide IF bandwidth while still maintaining the economy of a single channel system. Further improvements include the design of a phase cal detector and an input module compatible with NASA geodetic S/X receivers. Finally, efforts are being coordinated with ISTS so that record terminals developed for the Radioastron project can be interfaced to the CGLBI system.

We attempt to determine optimal configurations of six antennas for the proposed Berkeley Illinois Maryland Array. The instrumental response is used as a performance measure. A two dimensional sine function is chosen as the ideal beam, supported by theoretical considerations. A mean square comparison with this ideal is used to perform optimizations for arrays of various resolutions, using the current station locations at Hat Creek. Configurations for larger fields of view are also discussed, employing two days of coverage with six antennas.