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Seeing measurements with autonomous, short-baseline shadow band rangers

2010; SPIE; Volume: 7733; Linguagem: Inglês

10.1117/12.857643

1996-756X

Guus Sliepen, Aswin P. L. Jägers, Felix Bettonvil, Robert H. Hammerschlag,

Stellar, planetary, and galactic studies

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, C 2 n (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 C 2 n (h) profile and a value for the Fried parameter r 0 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.