Is that really your Strehl ratio?

Strehl ratio is the most commonly used metric for adaptive optics (AO) performance. It is also the most misused metric. Every Strehl ratio measurement algorithm has subtle differences that result in different measured values. This creates problems when comparing different measurements of the same AO system and even more problems when trying to compare results from different systems. To determine how much the various algorithm difference actually impacted the measured values, we created a series of simulated point spread functions (PSF). The simulated PSFs were then sent around to the various members of the project who then measured the Strehl ratio. The measurements were done blindly, with no knowledge of the true Strehl ratio. We then compared the various measurements to the truth values. Each measurement cycle turned up impacts which were further investigated in the next cycle. We present the results of our comparisons showing the scatter in measured Strehl ratios and our best recommendations for computing an accurate Strehl ratio.