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The next generation of adaptive optics (AO) systems will require tomographicreconstruction techniques to map the optical refractive index fluctuations,generated by the atmospheric turbulence, along the line of sight to theastronomical target. These systems can be enhanced with data from an externalatmospheric profiler. This is important for Extremely Large Telescope scaletomography. Here we propose a new instrument which utilises the generalisedSCIntillation Detection And Ranging (SCIDAR) technique to allow highsensitivity vertical profiles of the atmospheric optical turbulence and windvelocity profile above astronomical observatories. The new approach, which werefer to as 'Stereo-SCIDAR', uses a stereoscopic system with the scintillationpattern from each star of a double-star target incident on a separate detector.Separating the pupil images for each star has several advantages including:increased magnitude difference tolerance for the target stars; negating theneed for re-calibration due to the normalisation errors usually associated withSCIDAR; an increase of at least a factor of two in the signal-to-noise ratio ofthe cross-covariance function and hence the profile for equal magnitude targetstars and up to a factor of 16 improvement for targets of 3 magnitudesdifference; and easier real-time reconstruction of the wind-velocity profile.Theoretical response functions are calculated for the instrument, and theperformance is investigated using a Monte-Carlo simulation. The technique isdemonstrated using data recorded at the 2.5 m Nordic Optical Telescope and the1.0 m Jacobus Kapteyn Telescope, both on La Palma.

Stereo-SCIDAR: Optical turbulence profiling with high sensitivity using a modified SCIDAR instrument