The term very-long-baseline interferometry (VLBI) is self-explanatory, but is taken to imply a radio telescope interferometry technique suited to baselines sufficiently long to make real-time processing of the signals unwieldy. The signal data as well as its timing are stored at each telescope and later processing of the collected data determines the exact direction from which the signal came, allowing telescopes far apart (e.g., thousands of miles) to be used. Its use has achieved angular resolutions in the 10 microarcsecond range. VLBI arrays often use existing distantly-separated telescopes, and may be short-term projects, such as for specific surveys. Some VLBI arrays:
A recent development is electronic very-long-baseline interferometry, which is near-real-time transmission of the data for immediate analysis.
While VLBI clearly is useful for observing sufficiently bright radio sources, it offers as a byproduct, measurement of changes in the distance between receivers, down to the millimeter range, and reveals the effects of plate tectonics.