LOFAR uses a large number of low-cost sensors (antennas, geophones and more) and relies on broad-band datalinks and advanced digital signal processing to implement the majority of its functionality in (embedded) software.
The system details for the geophysical application of LOFAR is described here and the description of the system of the agricultural application can be found here.
LOFAR will be the first large radio telescope system, wherein a huge amount of small sensors are used to achieve its sensitivity instead of a small number of big dishes. The main reasons for this are:
For the astronomy application, LOFAR is an aperture synthesis array composed of phased array stations. The antennas in each station form a phased array, producing one or many station beams on the sky. Multi-beaming is a major advantage of the phased array concept. It is not only used to increase observational efficiency, but may be vital for calibration purposes. The phased array stations are combined into an aperture synthesis array. The Remote Stations are distributed over a large area with a maximum baseline of 100 km within the Netherlands and 1500 km within Europe.
- For the low frequencies involved in LOFAR traditional telescopes would be very large and hence costly.
- Pointing can be done electronically, without using moveable parts and hence saving on maintenance costs.
- It enables pointing in multiple directions at the same time.
- It provides operational flexibility (e.g. rapid switching between observations is possible).
The main subsystems constituting the LOFAR radio telescope are:
Sensor Fields - stations:
A station selects the sky signals of interest for a
particular observation out of the total sky. This process results in
one or multiple beams onto the sky. Additionally the station is able to
store (raw) antenna data.
Wide Area Networks (WAN)
: The WAN is responsible for the transparent transport of all the beam data (the beam signals on the sky) from the stations to the central processor.
Central Processing Systems (CEP):
The central processor is responsible for the processing and combination of the beam data from all stations in such a way that user data is generated as was specified by the user.
to control and provide user interfaces:
- Scheduling, Administration and Specification (SAS): Given the specification, the main responsibility of SAS is to schedule and configure the system in the right mode. Additionally SAS facilitates the possibility to store metadata of the system for a long term and make that information accessible for the user.
- Monitoring And Control (MAC): The main responsibility of MAC is to control the system (in realtime)
based upon the actual configuration of that moment. Additionally, MAC facilitates the (realtime) monitoring of the present state of the system.
- System Health Management (SHM): SHM is identified as an autonomous block to predict and act on failures of the hardware before it actually fails. Ideally it should even pinpoint which system component is the cause of a failure. The reason for considering this block separate from MAC is because of the scale of the system and the percentage of time the system should be effectively operational.
The Architecturial desgin documents of the various components and of the LOFAR system and additional documentation can be found here.
Figure 1: LOFAR system architecture.