7 Comparison between effective and expected performance

From the mirror commands that were recorded in closed loop, the BOA group is also able to calculate the residual variances of the Zernike coefficients. This numerical calculation, that uses an atmospheric model, has been performed up to J=45assuming that the wavefronts distortions corresponding to higher Zernike orders are not corrected. In fact the reconstruction of the coefficients for J>45 is not significant because their values are comparable with the ones of the reconstruction noise.

Figure 10: Mean radial profiles for $\frac{D}{r_0(\mathrm{vis})}=17$. Full lines: recorded profiles with and without AIC (no selection of images). Dashed lines: simulated profiles with and without AIC. Dotted line recorded profile with AIC with substraction of the profile of a diffraction pattern weighted by RT.<d2>. Horizontal scale: arcseconds on the sky

From the values of the variances derived from the wavefront sensor data, we are able to simulate radial profiles given by AIC (Paper I). The simulation takes into account the spectral bandwith and the telescope obstruction. The observed profiles cannot be readily compared to the simulated ones, because of the energy contribution from the OPD variations. In order for the comparison to make sense we have substracted a diffraction pattern weighted by RT.<d²> from the observed profile which practically yields the profile we should have observed with AIC free from OPD fluctuations. In Figs. 10, 11, 12 we compare simulated and obtained profiles with and without AIC for three different conditions of turbulence (respectively $\frac{D}{r_0(\mathrm{vis})}=17$, $\frac{D}{r_0(\mathrm{vis})}=43$, $\frac{D}{r_0(\mathrm{vis})}=52$). From these figures we see that there is a good agreement between the simulated profiles and the "observed-OPD removed'' profiles, which shows the relevance of the analysis appearing in Paper I and regarding performance of AIC under turbulence. Then, when the mean values of the residual variances for a given AO are available, we can predict realistic and reliable profiles of the residual energy distribution at the output of AIC.