Wind speed measurement from Shack Hartmann Wavefront Sensor data: An experimental review of cross-correlation peak detection

The mean velocity of the atmospheric wind is an important parameter in characterizing the turbulence above an astronomical telescope. Real-time wind velocity measurement is exceedingly essential to update the design metrics of the adaptive optics system periodically to improve the dynamic performance. A Shack Hartmann Wavefront Sensor (SHWS), which is generally used in astronomical telescope adaptive optics systems for wavefront sensing, can be simultaneously used for wind speed estimation and this means of wind speed estimation needs special attention due to the ease of its implementation. In this paper, we discuss in elaborate the experimental evaluation of the wind measurement from the calculation of the two dimensional cross-correlation function. Adopting the peak technique, we find that the identification of the peak can be made accurate by using the computation cost effective 3-point parabolic interpolation technique, which is shown to behave close to the 3-point Gaussian interpolation. Also, it is shown that the time interval chosen for the calculation of the cross-correlation plays a vital role in optimal performance. For small time interval case, the interpolation techniques do not yield correct results. In this case, it is shown that the iteratively weighted center of gravity algorithm is more suitable.