Very-Long-Baseline Radio Interferometry: The Mark III System for Geodesy, Astrometry, and Aperture Synthesis

Area of Science:

• Radio astronomy
• Geophysics
• Astrophysics

Background:

• Very-Long-Baseline Interferometry (VLBI) is crucial for high-precision measurements.
• The Mark III VLBI system offers advanced capabilities for data acquisition and processing.

Purpose of the Study:

• To detail the capabilities of the Mark III VLBI system for astrometric and geodetic applications.
• To demonstrate the system's accuracy in measuring antenna positions and celestial source coordinates.

Main Methods:

• Simultaneous recording of dual-band radio signals (2.2-2.3 GHz and 8.2-8.6 GHz) at multiple antenna sites.
• Correction for ionospheric effects using dual-band recordings to determine precise group delays.
• Processing of large bandwidths (up to 28 contiguous bands) for mapping radio source brightness distributions.

Main Results:

• Determination of relative group delays with uncertainties under 50 picoseconds for intense radio sources.
• Measurement of baseline lengths between antennas with 1-sigma uncertainties of approximately 5 centimeters.
• Determination of celestial coordinates of radio sources with 1-sigma uncertainties of about 3 milliseconds of arc.
• No significant evidence of change in measured baseline lengths or source positions over time.

Conclusions:

• The Mark III VLBI system provides high accuracy for geodetic and astrometric measurements.
• The system is capable of mapping compact radio sources with flux densities below 1 millijansky.
• Demonstrated stability of terrestrial and celestial reference frames measured by the system.