Atmospheric spatial and temporal seeing monitor using portable amateur astronomy equipment

Accurate knowledge of the spatial and temporal seeing has become increasingly important as AO systems move from being specialised instruments to standard equipment at large ground-based telescopes. While monitors that measure the spatial seeing scale are now commonplace, devices capable of measuring temporal seeing parameters are much rarer since the sampling requirements are severe. Nevertheless, such information is vital if the bandwidth and control requirements for active and adaptive systems at state-of-the-art telescopes and optical/IR interferometers are to be correctly specified. In this paper we describe a cheap, yet robust, Differential Image Motion Monitor Which Is Transportable (DIMMWIT) that can make both spatial and temporal seeing measurements. It samples starlight at rates up to 500Hz but contains no mechanical parts and uses only technology available to amateur astronomers. We review the design and performance of the device and present examples of results from routine use at the Cambridge Optical Aperture Synthesis Telescope (COAST) site in the UK. An identical system is also being tested at the Magdalena Ridge Optical Interferometer (MROI) site in New Mexico.