Introduction

One of the challenges of analysing data from the Murchison Widefield Array is correcting for the effect of the primary beam -- the telescope's inbuilt response to the sky -- on the astronomical signal. To do this, we need to know that response down to a high accuracy, in both polarisations to which the array is sensitive. Simulations go some way toward modelling the beam, but effects such as cross-coupling between the dipoles are complicated and non-linear. Efforts have previously been made to measure the beam using astronomical sources and satellite passes, but as neither of these kinds of source are well-characterised themselves, it is difficult to extract the beam from the data.

A simple solution to this inverse problem is to use a well-characterised source, with a known frequency and a known beam, placed at a known position. We then find the issue that the far-field of the MWA starts at 20m height over the instrument - so how do we place a radio-frequency source at at least that height?

Fortunately, over the last two years, there has been a huge leap forward in the development of miniature unmanned aerial vehicles, capable of flying and hovering up to a kilometer high. The largest, the Octocopter, can carry payloads of up to 1kg, and fly for half an hour at a time. After a feasability study, the Octocopter was purchased. This blog forms a record of flight-testing and eventually the tile measurement project.