Monday 21 March 2011

How do KAIRA and LOFAR work? — Part 1 : Introduction

KAIRA (Kilpisjärvi Atmospheric Imaging Receiver Array) is a radio receiver system. It can measure very faint radio signals and determine very precisely which directions those signals are coming from. It uses LOFAR antennas and signal processing to accomplish this. If you ignore the details of how the data are processed and interpreted, you can safely say that antennas of LOFAR and KAIRA are doing the same sort of thing.

LOFAR (LOw Frequency ARray) is a radio telescope, designed by the Netherlands Institute for Radio Astronomy — ASTRON. Unlike the so-called traditional radio telescopes, which use large parabolic dishes, LOFAR has fields of antennas, which do not move. Instead, it uses electronics and computing to change which way the telescope is looking in the sky. With no moving parts, one is often asked how it works. The problem is that the answers often come in two extremes.

The first is that there is some glib statement that simply reiterates how the 'signals from all the antennas are combined to emulate a large telescope and that the telescope uses digital technology to change the direction that it points in the sky'.

The second is a full-blown lecture course that starts 'Consider electromagnetic radiation from direction s from a small elemental solid angle dΩ, at frequency υ, within a frequency width dυ'. From there it quickly degenerates into page after page of equations.

For the next few weeks we’ll be posting a series of articles to the KAIRA web log in addition to our regular photographs and reports. These articles will steer the middle ground between the two extremes. Of course the entire topic can be extremely complex, and there are many complications and assumptions that we’ll have to skip over to avoid getting bogged down in the detail. (For the experts out there, please indulge us these simplifications.) And yet, we intend to go into sufficient detail, step-by-step and without mathematics, to explain with words and illustrations how KAIRA and LOFAR will accomplish their amazing observations.

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