Calar Alto joins the “dark side” of the Spanish national network of optical fibre

The Calar Alto observatory will be integrated into RedIRIS-NOVA, the Spanish RedIRIS network of high-capacity dark fibre. This EU investment with MRR funds, worth about €2 million, will allow a better accessibility to the various datasets generated each night of observation by the multiple instruments of its telescopes, as well as open the possibility to access future research projects that require high bandwidth.

Calar Alto, like all large contemporaneous astronomical observatories, is located on top of a mountain, in the Sierra de los Filabres at 2168 meters above sea level. The site was chosen more than half a century ago, thanks to the quality of its sky, by German scientists who were searching the best place to observe stars and distant galaxies from the Old Continent.  

interior2This privileged location in Eastern Andalusia, quite far away from the cities and thus, less polluted by public lighting, offers indeed the clearest and most stable skies in continental Europe. But its relative isolation, at almost 2200 m altitude, also implies a more complicated access for the road network (particularly in winter) as well as for the external communication network, with the unstoppable development of the internet in the 90s of the 20th century.

Like for any current large science center, an internet connection offering stability and a high capacity is critical for the Calar Alto observatory, in particular to distribute to the astronomical community the data collected by its four largest telescopes (with mirrors larger than 1.2 m in diameter) and instruments, observing 365 nights a year. The wide-ranging instrumentation (including live monitors, checking every minute and even seconds, the quality of the sky), can generate a large amount of data, like the weather station which has been operating uninterruptedly since July 1997.

The valuable astronomical data coming from every telescope and its instrument, digitizing the photons that came out (millions of) years ago from a star in our galaxy or another "island universe", as well as the meteorological data collected every night, have to be made available to the Calar Alto scientific user community almost immediately.

The data of each observation, in addition to being saved temporarily on local disks (with the virtualization and the archive, Calar Alto reaches a quantity of more than 0.5 PB of data), are transmitted abroad from the center's network over the Internet. In particular, the astronomical data are sent and stored permanently in the Spanish virtual observatory archive, physically located at Center for Astrobiology (CAB-CSIC/INTA) in Madrid.

radioenlace enCurrently, it must be emphasized that remote observations are made with the 1.23 m and with the Schmidt telescopes, the latter being used by the European Space Agency (ESA). This kind of observations from a distance logically requires a network with a considerable bandwidth and above all, a great stability, not only for the transfer of spectra and images from Calar Alto to the remote place of observation, but also for the safety of the telescopes and instruments. Moreover, with the advent of teleworking for the CAHA staff, the need for a reliable, secure network with sufficient capacity has also increased.

It is important to mention that telephone cables (copper or fiber) have never reached Calar Alto. All transmissions (both telephone and data) have so far been carried out by radio-link systems. Specifically, for data and for the Internet, a microwave link has been set up between two large antennas, located on the mountain on one side, and within the University of Almería (UAL) campus on the other side, with a separation of almost 50 km in a straight line and direct sight.

The connection to the Spanish scientific network (RedIRIS) is done through a router of the Research and Scientific Network of Andalusia (RICA, managed by the Scientific Computer Center of Andalusia, CICA) and located in the very same UAL (university with whom Calar Alto also has also signed a collaboration agreement). Although the bandwidth has gradually increased from the initial 9.6 Kbps to the current 800 Mbps, this method of connection to the general network has physical limitations.

The quality of this kind of connection can also get reduced by the weather conditions, extreme at times, which happen at the observatory. Particularly during winter storms: intense snowfall, strong wind gusts over 200 km/h (ca. 125 mph) and formation of thick layers of ice on the antenna (see above picture), which may cause momentary interruptions of the connection or a temporary decrease in bandwidth.

The maintenance and constant improvements made by the Calar Alto staff, both at the observatory and on the antenna located on the UAL campus as well, have allowed us to maintain a high degree of reliability outside of some episodes of adverse weather. Yet, as it is well known, the performance, safety, reliability and above all the possibilities offered, for the future, of a fibre cable, far exceed the ones of any radio link.

The only stable, high-capacity network connection between the observatory and the rest of the world has to go through optical fibre. Physically, it is the same technology which is used in virtually all recent instruments mounted on our telescopes: "single-fibre" spectrographs like CARMENES or other ones multi-fibres like PMAS (both mounted on the 3.5-meter telescope) include optical fibres transporting the information in the form of light: the celestial photons captured by their ultra-sensitive sensors are then also transported as (now "terrestrial") light signals to computers,  dedicated to each instrument, which store all the digitized astronomical information on their disks for a subsequent data reduction and analysis.

interior1.pngLikewise, the internal “backbone” of the Calar Alto network is entirely made of optical fibres, which currently allow bandwidths between 10 Gbps and 20 Gbps. Optical fibre technology has implied a qualitative leap in the transport of information transport. Just as a reminder, there is nothing faster than light in the Universe, with the photons reaching almost 300,000 km per second.

The difficulties due to the distance to the connection point and to the complicated orography of the terrain around Calar Alto before connecting with the RedIRIS national scientific network, based on the dark fibre technology, is an added difficulty and a huge challenge for the optical fibre connection project to the observatory.

Fortunately, this project is going to materialize soon thanks to the agreement signed between Calar Alto and back in 2021, which will be executed through RedIRIS, and which is part of one of the actions foreseen in the Uni-Digital Plan, within one of its four lines of action, called "Projects of infrastructures and common ICT services". The Uni-Digital Plan is also measure #10 of component #21 of the Recovery, Transformation and Resilience Plan for Spain with European Funds “Next Generation EU – MRR”, which aims at modernizing and digitalizing the education system.

The agreement signed between Calar Alto and on June 14th, 2021, specifies the soon-to-come connection of the observatory to the exterior through the RedIRIS-NOVA optical backbone network of dark fiber, with an irrevocable right of use of a minimum of 12 years, ensuring a high capacity connection (of at least 100 Gpbs) reliable, safe and flexible. Finally, it will be the large communication company Telefónica which will supply the fibre connection to Calar Alto, with a contract awarded on January 13th, 2023 for a total value of € 2,030,000578.51 (VAT excluded), and an execution period of 12 months from the date of adjudication.

Enrique de Guindos, head of the IT department at the observatory, emphasizes that "the arrival of the fibre to Calar Alto is undoubtedly a historic milestone for the observatory. Never before have we been able to get a wired connection that communicates us with the rest of the Spanish scientific network and with the rest of the world. And it has been a long process, started in 2009, to get to where we are now."

"For a scientific centre like Calar Alto, it is essential to have a connectivity that allows us not only to offer a currently stable and sufficient bandwidth, but also the growth projection necessary to address future projects that require bandwidths much higher than the current one. And this is something that the RedIRIS dark fibre will bring us", adds de Guindos.

More information:

Calar Alto Observatory:


Enrique de Guindos - guindos @  (+34) 950632517

Calar Alto Observatory is one of the infrastructures that belong to the national map of Unique Scientific and Technical Infrastructures (Spanish acronym: ICTS), approved on March 11th, 2022, by the Science, Technology and Innovation Policy Council (CPCTI)


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