Sites Inria

Version française

Astrophysic

Isabelle Bellin - 13/03/2013

Inria researchers at the heart of the action around ALMA, the world's largest radio telescope, in Chile

Some of the ALMA's antennas - ©ALMA

From a plan started in 1995, ALMA, the fruit of a partnership between Europe, North America, Japan and Chile, was officially opened on Wednesday, 13 March, after taking ten years to build. Using its unprecedented radio images, astronomers hope to discover distant galaxies and better understand the processes by which stars are formed. Proper operational use of the giant telescope entails real-time interpretation of thousands of parameters. Emmanuel Pietriga, with members of the Massive Data team at Inria Chile,  is in the country for two years, developing the instrument's control user  interfaces.

In northern Chile, edged by the Andes mountain range and at an altitude of 5,000 metres, the Chajnantor plateau in the Atacama Desert , one of the driest areas on earth, has practically no cloud cover, light pollution or radio interference. It is a harsh and spectacular environment surrounded by snow-capped volcanoes, where temperatures fluctuate between -20 °C and 20 °C. This is where the ALMA radio telescope has been built. This huge facility will eventually comprise 66 radio telescopes , dish antennae made of metal each weighing over 100 tons, the majority 12 metres in diameter. With the most distant being 15 kilometres away, these  antennas work as a coherent whole, like a single vast virtual dish 15 kilometres across . It is the largest facility of its type, and will make it possible to obtain excellent resolution radio images at millimeter and sub-millimeter wavelengths  (as opposed to the  visible or infrared light captured by optical telescopes). These waves, emitted by the interstellar medium from cold or dark areas of the universe, will enable the oldest galaxies to be observed, the composition of the interstellar medium to be understood, and more to be discovered about the formation of solar systems and the universe.

Electromagnetic radiation is converted into images by producing images through the assignment of colours to each frequency  and brightness based on radiation intensity. Several frequencies are combined to produce an image. Ultimately, astronomers can compare these radio images with images produced from visible light. ALMA began scientific observations in late 2011. All the image rebuilding work is performed on a supercomputer designed specifically for ALMA, that performs as well as the most powerful general-purpose computer. Its role is to synchronise the data supplied by all antennas, on the basis of their position and timing of the signal received, using the principle of interferometry generally used for radio telescopes.

Antennae Galaxies composite of ALMA and Hubble observations - ©ALMA

"For this system, infinitely more complex than optical telescopes, to work properly, all the equipment has to be  constantly monitored and the vast quantity of data collected has to be interpreted in real time , so as to react quickly in the event of a malfunction or poor quality in the data observed," says Emmanuel Pietriga, a researcher at Inria Chile, the organisation that manages Inria's partnerships with Chile. This entails checking thousands of variables for each antenna, measuring phase, amplitude, temperature, water vapour levels, etc. The acquisition time for each image is measured in tens of minutes, each needs to be of the best possible quality.

"We have been developing specific user interfaces  for three years", the researcher adds. "We have adapted our human–computer interface concepts and tools for displaying vast quantities of data to ALMA's case. From the outset, we worked jointly with the astronomers and telescope operators on transferring our solutions to ALMA's massive scale . Emmanuel Pietriga eventually hopes to optimise data display on the many screens in the control room to better share information, with a greater or lesser level of detail for the thousands of graphs, maps and diagrams to be monitored. With ALMA scientists , he is working at the base camp, where the data from the remote-controlled antenna arrays is collected, its altitude of 2,900 metres making for a more welcoming environment than the Chajnantor plateau.

Denis Barkats , an astrophysicist, is a member of the ALMA commissioning team

"The quality of the interfaces developed by Inria ensures ALMA works properly"

It's quite simple. Without the work of Emmanuel Pietriga and his team, there would be so much data to display at the same time that it would be impossible for us to control all the telescopes, assess the data quality and diagnose malfunctions. We would have wasted a lot of time and probably lost a lot of data. We didn't anticipate this user interface problem. It arose as we went along, once about ten telescopes had been installed on the site and synchronised. Quite simply because the software developed for ALMA is sized just as for other radio telescopes, i.e., for around ten telescopes at most. However, ALMA has 66 of them. At that scale, the data supplied becomes unmanageable. We find ourselves with a matrix of over 2,000 points, ten screens to monitor, too many colours and too much text to read. Working with Emmanuel and his team was not part of the original ALMA development plan. His first involvement was on a very specific issue. But we quickly realised that he could bring ALMA guaranteed operating efficiency and stability. His methods and skills complement our own. He spends several days watching how we work, then we discuss it and he subsequently shows us the improvements he could deliver on the basis of other examples, such as how to replace a long text with a graph, or prioritising data to focus on the key information. We think it's magical, an unexpected bonus! At the same time, he is also working with the developers to enhance their software. This optimisation work has already made good progress, and it should be finished by the end of 2013.

Keywords: Inria Chile Radiotélescope Équipe Massive Data Astrophysique Interaction homme-machine

Top