06 Feb 2017

Stereo-SCIDAR is a high-altitude resolution and high sensitivity optical turbulence profiler. By measuring the intensity pattern of two nearby stars astronomers can triangulate the altitude and strength of optical turbulence in the Earth's atmosphere. And by introducing a temporal delay between these two signals, they can also calculate the horizontal velocity of each layer.
Stereo-SCIDAR was developed by Durham University, UK as part of the Canary Adaptive-Optics demonstrator project (CANARY) on the William Herschel Telescope, and it has been operated on the Isaac Newton Telescope for a total of 28 nights.
In their latest results, Osborn et al. (MNRAS, 464, 3998) validate the Stereo-SCIDAR turbulence velocity profiling with concurrent measurements for balloon borne radiosonde and General Circulation Model (GFS).
They also show some examples of typical dynamic profiles (strength and velocity), finding that the atmospheric turbulence profile above La Palma is often complex. They regularly observe structure within turbulent zones, with several distinct and continuous velocity distributions. This complicated structure has significant impact on the performance of wide-field Adaptive-optics systems.

[Image]
This figure shows the atmospheric turbulence profile above La Palma throughout a night, the lower plot shows a sub-set of detected wind vectors overlaid. We see that the optical turbulence changes in altitude, strength and velocity over short and long time scales.