There is growing interest in measuring seeing at existing and prospective telescope sites. Several methods exist to quantify
seeing, one among them is by measuring the scintillation of solar or lunar light using a photodiode. A shadow band
ranger (SHABAR) analyses the covariance of the signals from an array of such photodiodes, which allows for the spatial
resolution of the index of refraction above the SHABAR device. This allows one to estimate the index of refraction
structure parameter as a function of height, C2n(h).
Although a SHABAR has a limited range compared to a differential image motion monitor (DIMM) or the latest
wavefront sensors, the advantage is that it does not need telescope optics to work. A SHABAR device can be made very
compact and can operate independent of other instruments. We describe the design of such a SHABAR device with six
photodiodes that can operate virtually indefinitely without requiring human intervention.
An inversion algorithm is used to convert the raw scintillation signals of the photodiodes to the desired C2n(h) profile
and a value for the Fried parameter r0 at height zero. We show that it is possible to perform inversions of 10 s periods in
real time on relatively low-end hardware, such as an Intel Atom based computer, which allows the results to be presented
live to astronomers, who can use this information to help make decisions about their observation schedule.
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