LOFAR in a Nutshell
The LOw Frequency Array, or LOFAR for short, is a digital radio telescope that spans several European countries with its core in the Netherlands. LOFAR leads the way for a new generation of digital radio interferometers that consist of a multitude of antenna fields spread over large distances. The radio waves that are received by thousands of antennae are sampled digitally, the signals are transmitted over large baselines via high-speed (10 Gb/s) fibre cables to a high-performance computing facility, where the radio images are synthesized in real time. This way, LOFAR acts like a huge digital camera that scans the entire sky in very low radio frequencies. LOFAR opens up a new window to the Universe by observing at very low radio frequencies (10 - 240 MHz). In this range of frequencies the sky is largely unexplored. Here LOFAR offers unprecedented angular resolution and sensitivity and, thus, promises new discoveries and exciting science. Moreover, LOFAR is also an important scientific and technological pathfinder for the next generation of radio telescopes, the Square Kilometre Array (SKA). The SKA will be the world's premier imaging and surveying telescope with a combination of unprecedented versatility and sensitivity that will be a ~600 Mio. Euro project.
LOFAR was developed by a consortium of institutes, universities and industrial parties, led by ASTRON, the Netherlands Institute for Radio Astronomy. The heart of LOFAR lies in the northeast of the Netherlands and spreads over several European countries. The LOFAR core has 24 stations, which are complemented by 14 remote stations in the Netherlands. Thirteen international stations in Germany (6), Poland (3), France (1), Ireland (1), Sweden (1) and United Kingdom (1) are currently operational.
With LOFAR, astronomers will get a glimpse at the epoch of formation of the very first stars in the universe, they will explore extragalactic magnetic fields, chart millions of galaxies, monitor solar activity and search for extrasolar planets.
LOFAR stations consist of fixed antennas that have no moving parts. The whole array is made up of about 51 stations, each roughly as big as a football field. Each LOFAR station has two separate arrays of antennas. These are referred to as the Low-Band Array (LBA) and High-Band Array (HBA). The LBA is optimised for the frequency range 30–80 MHz and the HBA for 120–240 MHz. The gap between the two bands is where FM radio is broadcast. Phased arrays such LOFAR work by exploiting the physical effects of constructive and destructive interference. By adding phase delays between the signals received at every single antenna, the telescope can me made most sensitive in on particular direction of the sky. This so-called beam can be steered electronically across the sky. The signals from all station are "synthesized" into images in one big supercomputer that is located in Groningen (NL).
In collaboration with the University of Bielefeld, Hamburger Sternwarte constructed a LOFAR Station in Norderstedt, close to the City of Hamburg, which is in operation since 2015 (open pull-down menu below for more information).
LOFAR in Hamburg
The LOFAR station DE 609 in Norderstedt is the sixth German station, which came into operation in 2015. The station is owned by the Universities of Hamburg and Bielefeld and is part of a network of more than 50 similar stations spread over Europe. The network forms the International LOFAR Telescope (ILT), which is operated by the radio observatory ASTRON in the Netherlands on behalf of all partners of the ILT. The ILT is used to make images at radio frequencies. Being owner of a station the research groups in Bielefeld and Hamburg have privileged access to these images.
The hardware of the stations is mechanically relatively simple and inexpensive to set up. The innovation lies with the requirements for data transmission and with signal processing in the central supercomputer system in Groningen. The optical fibers have to transport several gigabit of data per second and the computer has to process the data from all stations in real time. And this 24 hours in seven days a week. LOFAR is therefore a real child of today's digital age.
The radio signals coming from the sky are extremely weak. In order to detect them, the radio emission generated by humans have to be filtered out. Radio waves are used for example for the transmission of radio and television and for mobile phones. As little radio radiation as possible should be generated in the vicinity of the LOFAR stations. The station antennas have the sole task of listening into space and do not emit any signals themselves. Except during occasional repair and maintenance work, the station, which is surrounded by a wooden fence, measures fully automatically without human presence. Visitors are welcome: There are two information boards that provide information about LOFAR at the entrance to the station. Video surveillance is made continuously for safety reasons.
DE 609 Norderstedt WebCams
LOFAR Station Norderstedt of the Universities Hamburg and Bielefeld is located at Harthagen street in Norderstedt, a town north of Hamburg. The station's coordinates are 53° 41' 55.1" North, and 9° 58' 10.4" East. Two public displays located near the entrance gate provide information for visitors. For security reasons the station is monitored by a CCTV system.
DE 609 images shown below are updated every few minutes.
|Low Band Antennas|
|High Band Antennas|