Tuesday 04 March 2025
Scientists have made a significant breakthrough in the field of geodesy, allowing them to correct for a long-standing issue that has been affecting their measurements. Geodesy is the science of measuring the size and shape of the Earth, and it’s crucial for our understanding of the planet’s rotation, tides, and even climate change.
For decades, scientists have been using Very Long Baseline Interferometry (VLBI) to measure the position and movement of celestial objects. VLBI works by combining signals from radio telescopes around the world, effectively creating a virtual telescope with a diameter that spans thousands of kilometers. This allows scientists to pinpoint the location of objects with incredible accuracy.
However, there’s been a problem. Many of these celestial objects, such as active galactic nuclei (AGN), are not point-like sources of radiation. Instead, they have complex structures that can affect the measurements taken by VLBI. This is known as source structure, and it’s been causing errors in geodetic data.
To address this issue, scientists have developed a new method for correcting for source structure in VLBI visibility data. Visibility data refers to the output of the DiFX software correlator, which combines signals from multiple radio telescopes. The new method uses a software package called VieSOFT to remove the impact of source structure from these data.
The process works by modeling the brightness distribution of the celestial object using Gaussian components. These components are then used to calculate a correction term that is subtracted from the original visibility data. This correction term accounts for the effects of source structure on the measurements taken by VLBI.
To test this new method, scientists analyzed real VGOS (VLBI Global Observing System) data, which includes observations of several celestial objects with varying levels of source structure. They found that the corrected visibility data showed significant improvements in terms of image quality and closure delays.
Closure delays refer to the difference between the expected arrival time of a signal and its actual arrival time at different radio telescopes. These delays can be caused by a variety of factors, including the Earth’s atmosphere and instrumental errors. By correcting for source structure, scientists are able to reduce these delays and improve the overall accuracy of their measurements.
The implications of this breakthrough are significant. It will allow geodesists to make more accurate measurements of the Earth’s rotation, tides, and climate change. It may also enable the development of new technologies that rely on precise knowledge of the Earth’s shape and size.
Cite this article: “Correcting for Source Structure in VLBI Visibility Data: A Breakthrough in Geodesy”, The Science Archive, 2025.
Geodesy, Vlbi, Source Structure, Visibility Data, Viesoft, Gaussian Components, Closure Delays, Vgos, Difx, Correlator
