LOFAR Array configuration

 

The fundamental receiving elements of LOFAR are two types of small, relatively low-cost antennas that together cover the 10–240MHz operating bandpass. These antennas are grouped together into 48 separate stations distributed over the northeastern part of the Netherlands as well as in Germany, France, the UK, and Sweden.

An overview of the geographical location (in Google maps) of the stations can be found here.

 

Station Naming

The names of the stations are selected such that CS in the name means that they have two HBA fields rather than one. They are located either directly in the core area or nearby.

The RS in a station name denotes a remote station with only one HBA field and it is located in the Netherlands.

For international stations the appropriate country code is used. The numbers in a station name are somewhat historic but are unique for a station.

 

Core Stations 

For the majority of the array located in the Netherlands, the geographic distribution of stations shows a strong central concentration with 24 stations located within a radius of 2 km referred
to as the “core”. Within the core, the land was purchased to allow maximum freedom in choosing station locations. This freedom allowed the core station distribution to be optimized to achieve the good instantaneous uv coverage required by many of the Key Science Projects. At the heart of the core, six stations reside on a 320 m diameter island referred to as the “Superterp”; “terp” is a local name for an elevated site used
for buildings as protection against rising water. These Superterp stations, shown in Figure 1, provide the shortest baselines in the array and can also be combined to e ffectively form a single, large station.

 

Figure 1: The LOFAR Superterp.

 

A layout of where all LOFAR Core Stations are located, is shown in Figure 2. More locations are prepared than actual stations are placed in this phase of LOFAR. 

LOFAR core map

Figure 2: LOFAR core stations: grey - operational stations white-  locations for possible future stations. Note: Core stations CS103 (~1.7 km due west of the superterp) and CS302 (~2 km south-west of the superterp) do not appear on this map. 

 

Remote Stations 

 

Beyond the core, the 14 remaining LOFAR stations in the Netherlands are arranged in an approximation to a logarithmic spiral distribution. Deviations from this optimal pattern were necessary due to the availability of land for the stations as well as the locations of existing fiber infrastructure. These outer stations extend out to a radius of 90 km and are generally classified as “remote” stations. As discussed below, these remote stations also exhibit a di erent configuration to their antenna distributions than core stations. The full distribution of core and remote stations within the Netherlands is shown in Figure 3.

 

Figure 3:  Distribution of remote stations within the Netherlands located at distances of up to 90 km from the center of the array. Stations shown in green are complete and operational while yellow depicts stations that were under construction as of March 2013.

 

International Stations

Eight international stations are currently (early 2014) operational. They are in Germany: Effelsberg (DE601), Unterweilenbach (near Garching/Munich, DE602), Tautenburg (DE603), Potsdam-Bornim (DE604), Jülich (DE605), in the UK: Chilbolton (UK608), in France: Nançay (FR606) and in Sweden: Onsala (SE607). An overview of their location is given Figure 4.

 

Figure 4:  Current distribution of the European LOFAR stations that have been built in Germany (5), France (1), Sweden (1) and the UK (1). The color scheme for the stations is the same as in Fig. 2. A sixth German station located near Hamburg (shown in yellow) has recently begun construction and is expected to be online in 2015. Data from all international stations is routed through Amsterdam before transfer to CEP in Groningen, NL. For the German stations, data are first routed through Julich before transfer on to Amsterdam.

Current Status

There are 38 stations operational in the Netherlands (24 core and 14 remote stations) and 8 international stations operational in Germany (5), the UK (1), France (1) and Sweden (1). 4 more international stations will be built in 2014-2015, one in Germany (nearby Hamburg) and 3 in Poland.


Example UV Coverages

Below, we show the sample uv coverage plots (left) and synthesized beams (right) including all present and planned LOFAR stations. The uv coverage is calculated for a source at declination 48, and covers a 6 h track between hour angles of approximately -3 to +3 hours. One point is plotted every minute. Synthesized beams are calculated using uniform weighting, and using multi-frequency synthesis over the full LBA frequency range from 30–78 MHz. The top frames are for the 24 core stations only, middle frames include all 40 core and remote stations, and the bottom frames include all 48 core, remote, and international stations. 

 

 

The Figure below illustrates the instantaneous uv coverage (near transit at the same declination) for the same complement of stations, and shows the e ffect of the full 48 MHz bandwidth from 30-78 MHz on the uv coverage. In the left frames, one point is plotted every 0.2 MHz. 


Design: Kuenst.    Development: Dripl.    © 2014 ASTRON