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Researchers Use Drones to Calibrate the BMX Radio Telescope

At the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory, cosmologists have been experimenting with a prototype radio telescope, known as the Baryon Mapping Experiment (BMX).

To calibrate the BMX radio telescope, researchers mounted a small radio source to a quadcopter drone and then flew it over the telescope, making a zig-zag pattern over the telescope’s entire field of view. By comparing the drone’s known flight path from GPS signals to the radio signals picked up by BMX, the researchers are able to determine what signals were missed by the telescope. Image Credit: Brookhaven National Laboratory.

The prototype was developed at the laboratory in 2017 and serves as a testbed for developing calibration methods and controlling radio interference. The knowledge gained from the prototype could provide a method for Brookhaven to design a much larger radio telescope in association with other universities, international collaborators, and national labs.

A telescope of this kind would map neutral hydrogen over huge swaths of the universe, allowing scientists to gain a better insight into its accelerated expansion, as well as the nature of dark energy.

At BMX, successful experiments have earlier resulted in significant upgrades for the telescope, like the addition of three dishes. At present, the researchers have collaborated with scientists from Yale University and started testing a new calibration method that makes use of drones.

Traditional radio telescopes are often focused on sensitivity, but this telescope is all about calibration. We want to know exactly what the telescope sees with the accuracy of one part in a thousand, or better.

Anže Slosar, Physicist, Brookhaven National Laboratory

Slosar continued, “Eventually, we would propose building a telescope with thousands of dishes, but the calibration method would be the same. So, if we can show that we calibrated the prototype to the right precision, then we know we can do that for a larger telescope as well.”

For BMX to be calibrated with the help of a drone, the Yale collaborators fitted a tiny radio source to a quadcopter drone and then made it to fly over the telescope, thus creating a zig-zag pattern over the complete field of view of the telescope.

The scientists could identify what signals were missed by the telescope by comparing the well-known flight path of the drone from GPS signals to the radio signals that have been picked up by BMX.

This method of calibrating telescopes has been around for about 10 years, but it’s very hard to do in practice. One of the main difficulties is knowing exactly where the drone is with sufficient precision. We solved this problem by using a differential GPS (DGPS).

Emily Kuhn, Graduate Student, Yale University

Very high accuracy down to a centimeter, instead of a meter, is achieved by DGPS when compared to GPS, by using an additional ground-based station.

Also, the team is experimenting with a completely new calibration method that makes use of a small, fixed-wing plane. When compared to drones, the plane is faster and can fly for a longer time. Furthermore, it can easily fly back to the original point, making it quite easy for scientists to cross-check their outcomes; but the plane cannot hover like a drone.

Such calibration experiments are still under progress, and the Brookhaven team will continue its collaboration with Yale University to gather more information from the small plane and the drones.

This study was financially supported by Brookhaven’s Laboratory Directed Research and Development funding.


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