Abstract
This paper discusses some of the main error sources that affect use of the Slope Detection and Ranging (SLODAR) technique to recover atmospheric turbulence profiles from Shack-Hartmann wavefront sensor data. The most significant factor we address here is that of temporal sampling - we examine the effect of poorly-averaged slope correlations due to low wind speeds (or data sets that are insufficiently long) on spatial covariances of wavefront slopes. We discuss how this can affect the observed outer scale of the turbulence. A dual SCIDAR- SLODAR instrument is described that is ideally suited to exploring the impact of these effects and, potentially, correcting them. Some preliminary results from the instrument are presented.
Highlights
Slope Detection and Ranging (SLODAR) [1] is an optical turbulence profiling technique that can be implemented using a dedicated instrument or using wavefront slope measurements from a facility adaptive optics system
The dual SCIDAR-SLODAR instrument One approach to investigating temporal effects in SLODAR is to compare with simultaneous SCIDAR data; SCIDAR is not very sensitive to the outer scale and does not require such long datasets to provide well-averaged cross-covariance measurements
Wind correction of SLODAR response functions The wind velocity profile measured from SCIDAR can be used to improve the SLODAR response functions to account for the combination of translation velocity and finite temporal baseline
Summary
Slope Detection and Ranging (SLODAR) [1] is an optical turbulence profiling technique that can be implemented using a dedicated instrument or using wavefront slope measurements from a facility adaptive optics system. 3. SLODAR response functions A SLODAR response function is a model of the cross-covariance measured in response to a single layer of turbulence at a given altitude. (v) The temporal baseline of the measurement (i.e. the averaging time for the cross-covariance).
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