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  Issue No. 2302 Online Edition Sunday 7 February 2016 
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Ascension : New scientific equipment on Ascension Island.
Submitted by The Islander (Mario Anthony) 15.05.2014 (Article Archived on 05.06.2014)

Space-based communications systems have become increasingly prevalent in the world of today

Space-based communications systems have become increasingly prevalent in the world of today - including global navigation systems such as GPS, the media satellites that beam television and internet around the world, and imaging systems that observe and monitor the entire planet. The impact of the Earth’s atmosphere – especially the ionosphere – is a key design consideration for these systems. The ionosphere is the region of the atmosphere approximately 70 km – 1500 km in altitude. The study of the ionosphere, including its effects on space-based radio technology is one of the main research areas of the University of Birmingham Radio frequency And Space Technology group (RAST). The severity of ionospheric effects varies across the globe, with high and low latitudes experiencing greater impact than locations at mid latitudes. In addition, the ionosphere is particularly active in regions close to the magnetic equator. Ascension Island is located near the southern crest of this anomaly, making it well-placed for ionospheric study. Over the last eighteen months, the RAST group have been using data collected on Ascension Island to study the impact of the ionosphere on space-based radar systems. The effects of the ionosphere can significantly degrade the image quality of these radar systems. With the assistance of Babcock, ESA, Sure South Atlantic and Two Boats School, RAST has operated four GPS receivers on the island. GPS signals are very similar to those used by a typical space radar, but have the benefit of high availability – at any given moment there should be at least 6 GPS satellites visible anywhere in the world. The GPS data have been used to simulate the effect of the ionosphere on radar signals – and investigate the possibility of applying a correction to radar images to remove these effects. To extend this work, at the end of April 2014, a team of researchers from the University of Birmingham, UK and the Swedish Defence Research Agency (FOI), are spending time on Ascension, installing two real point targets, at sites near Long Beach and the old NASA facility. The sites were chosen in consultation with AIG and the Conservation Department. These targets are corner reflectors and completely passive in operation – they simply act as large (5m x 5m x 5m) ‘cats eyes’, reflecting radar signals directly back along the same path they travelled to the reflectors. The reflectors will be used with the new Japanese PALSAR-2 space-based radar, allowing the theory and methods developed with the GPS data to be confirmed and tested further with real radar data. The reflectors will remain in place for about a year, after which they will be dismantled, removed and the sites returned to their original condition. The RAST group would like to place on record their sincere gratitude and appreciation for the support and assistance given during their time on Ascension. Chris Mannix


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