GPS World

Tag: very long baseline interferometry

  • GPS plays role in black hole image

    Headshot: Tracy Cozzens
    Tracy Cozzens

    On April 10, the world looked in awe at the first image of a black hole. The image was captured by a world-spanning network of radio telescopes that together, using Orolia atomic-clock technology, create the Event Horizon Telescope.

    It zeroed in on the supermassive monster — 6.5 billion times the mass of the sun — in Galaxy M87 to create the image.

    As Innovation Editor Richard Langley explains, the technique used to capture the image — very long baseline interferometry (VLBI) — relies on GPS. (VLBI was the topic of Langley’s Ph.D. thesis.)

    VLBI links two or more radio telescopes that can be many kilometers apart, or even on different continents. VLBI is used in both geodesy and astronomy. There is also a practical GPS link to the Event Horizon Telescope. From the second of six simultaneously published open-access papers on the result: “All timing is locked to a 10-MHz [hydrogen] maser reference and synchronized with a pulse-per-second (PPS) Global Positioning System (GPS) signal…”

    “[T]he long-term drift of the maser [is] compared to GPS, measured by differencing [and plotting] the 1 PPS ticks from the maser and local GPS receiver. The vertical width of the trace is due to variable ionospheric and tropospheric delays of the GPS signal, while the long-term trend represents the frequency error of the maser. The drift measured from this plot, and its effects on the fringe visibility, are removed during VLBI correlation.”

    Image: Event Horizon Telescope Collaboration
    Image: Event Horizon Telescope Collaboration

    From the third paper: “In order to reconstruct the brightness distribution of an observed source, VLBI requires cross-correlation between the individual signals recorded independently at each station, brought to a common time reference using local atomic clocks paired with the Global Positioning System (GPS) for coarse synchronization.”

    Read more about the image and GPS.

  • Orolia technology synchronizes black hole photo telescopes

    Image: Event Horizon Telescope Collaboration
    Image: Event Horizon Telescope Collaboration

    Atomic clocks support world’s first black hole photo

    Orolia, through its joint venture company T4Science Inc. in Switzerland, supported the ground-breaking scientific initiative to capture the world’s first photo of a black hole, conducted by the Event Horizon Telescope (EHT) project.

    As a leader in maser atomic clock technology, Orolia provided the critical timing solution to synchronize telescopes around the world and create a virtual telescope the size of Earth to observe this deep space, supermassive object.

    Some of the world’s most advanced telescopes, located at challenging high-altitude sites, were synchronized with T4Science Masers to capture the sharpest image possible. Locations included volcanoes in Hawaii, Arizona mountains, the Spanish Sierra Nevada, the Chilean Atacama Desert and Antarctica.

    T4Science masers deliver ultra-precise time synchronization in the most challenging environments on Earth and in Space.

    The EHT project uses very long baseline interferometry (VLBI). This technology requires synchronization, phase stability and phase coherence between different telescopes within a few femto-seconds, and leverages the Earth’s rotation to form one Earth-size telescope.

    VLBI enables the EHT to achieve an angular resolution of 20 micro-arcseconds — enough to read a newspaper in New York from a sidewalk café in Paris.

    Orolia delivers this critical VLBI technology through its T4Science iMaser-3000 hydrogen masers. The iMaser-3000 is a VLBI atomic clock, supporting other mission-critical timing programs such as military and commercial satellite applications.

    “Orolia has been a proud supporter of space research and missions for more than forty years,” said Orolia CEO Jean-Yves Courtois. “As the world leader in resilient positioning, navigation and timing solutions, we develop precise, ultra-reliable technology for environments where failure is not an option.”

    Orolia’s proven timing solutions support many space agencies and research institutes worldwide, including ESA, NASA, Jet Propulsion Laboratory, SpaceX, the Centre National d’Étude Spatiales (CNES France), the National Physics Laboratory (UK), Deutsches Zentrum für Luft-und Raumfahrt (DLR Germany) and the Japan Aerospace Exploration Agency (JAXA), among others.