VLBI Technique Development

Haystack Observatory has a long history of contributions to Very Long Baseline Interferometry (VLBI), and is known for the development of state-of-the-art VLBI instrumentation and techniques. VLBI activities at the Observatory are primarily funded through NSF and NASA, though limited support from other sources is received. The VLBI group has a strong emphasis on the digital and mechanical engineering aspects of VLBI systems, utilizes the Haystack and Westford radio telescopes for VLBI measurements, maintains a VLBI correlator in round-the-clock operation, and has a vigorous program of scientific research.

VLBI 2010 -- Geodetic VLBI stands at the brink of a new era. Such societally relevant issues as climate change and natural hazards are placing ever increasing demands on performance. This comes at a time when problems with aging antennas, a deteriorating RFI environment, obsolete electronics, and high operating costs are making current levels of accuracy, reliability, and timeliness difficult to sustain. Attaining modern requirements for significantly greater accuracy, continuous data flow, and shortened times to product delivery challenge the continuing progress made by geodetic VLBI over the past 30 years. Fortunately, recent advances in antenna manufacture, digital electronics, and data transmission technology are enabling modes of operation unimaginable only a few years ago. Furthermore, the capital investment and reduced operating costs associated with the new technology make complete renewal of present infrastructure appear cost effective. A new instrument that will meet requirements for decades to come can now be envisioned.

Atmospheric Correction Research at Haystack -- The space geodetic techniques of Very Long Baseline Interferometry (VLBI) and the Global Positioning System (GPS), whose capabilities have been significantly enhanced in order to make accurate studies of the solid earth, are now recognized for their potential contributions to atmosphere research in both weather prediction and climate. The observations of both techniques are affected by the additional propagation delay through the neutral atmosphere, and it is this excess delay that provides information on the amount of water vapor in the atmosphere that is of such importance to the meteorologists.

Some of the principal projects and activities of the VLBI group at Haystack Observatory are as follows:

(*) NEW: Haystack Broad Band Development Memo Series
(*) Mark IV VLBI System -- Haystack played a central role in this international project to develop a next-generation VLBI correlator and recording system. The project has many aspects, perhaps the most important of which is a custom-designed VLSI correlator chip. The MkIV data acquisition system is documented in the Mark IV Memo Series.
(*) Mark 5 VLBI Data System
(*) e-VLBI -- 5th International e-VLBI Workshop
(*) VSI
(*) Digital Backend
(*) Mark IV VLBI Correlator -- An 8-station correlator used for processing of geodetic VLBI data. These data are used in studies of tectonic plate motions. The correlator is also used for processing of millimeter-wavelength astronomical VLBI observations.
(*) Haystack Observatory Postprocessing System (HOPS) -- A Unix-based software package designed to handle VLBI data from a MkIII or MkIV VLBI correlator. The capabilities of HOPS are designed to complement, and not overlap, those of AIPS, AIPS++, and the Caltech package. HOPS incorporates a fringe detection package optimized for the weak-signal and short coherence-time situation frequently encountered in millimeter VLBI.
(*) MkIII archival database covering 24 years of VLBI observations.