The design and operation of a new generation of digital imaging riometer systems developed by Lancaster University are presented. In the heart of the digital imaging riometer is a field-programmable gate array (FPGA), which is used for the digital signal processing and digital beam forming, completely replacing the analog Butler matrices which have been used in previous designs. The reconfigurable nature of the FPGA has been exploited to produce tools for remote system testing and diagnosis which have proven extremely useful for operation in remote locations such as the Arctic and Antarctic. Different FPGA programs enable different instrument configurations, including a 4 × 4 antenna filled array (producing 4 × 4 beams), an 8 × 8 antenna filled array (producing 7 × 7 beams), and a Mills cross system utilizing 63 antennas producing 556 usable beams. The concept of using a Mills cross antenna array for riometry has been successfully demonstrated for the first time. The digital beam forming has been validated by comparing the received signal power from cosmic radio sources with results predicted from the theoretical beam radiation pattern. The performances of four digital imaging riometer systems are compared against each other and a traditional imaging riometer utilizing analog Butler matrices. The comparison shows that digital imaging riometer systems, with independent receivers for each antenna, can obtain much better measurement precision for filled arrays or much higher spatial resolution for the Mills cross configuration when compared to existing imaging riometer systems.
The recently completed prototyping efforts for a new type of riometer, the Advanced Rio-Imaging Experiment in Scandinavia (ARIES), required the development of a uniquely flexible software architecture to deal with what in software engineering terms is referred to as a 'Wicked System:' Source, volume and type of data as well as required processing are only very loosely defined at the outset of the project. Speed, reconfigurability, remote control and data provenance are of major importance for the success of the project both during development and during operation of the deployed prototype. Details of the Advanced Riometer Components (ARCOM) component-based software architecture are presented. The software architecture is not specific to ARIES, and ARCOM components can readily be re-used in other, similar instruments.
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