Solar imaging experiment

Abstract : This report describes the experimental investigation of the possibility of real-time image compensation of the solar photosphere using the 21-channel Real-Time Atmospheric Compensation (RTAC) system developed at Itek. Observations were made using the 76-cm Vacuum Tower Telescope at Sacramento Peak Observatory in June 1979 and March 1980. During the second period, observations were also made of single and double stars to obtain data on the isoplanatic patch. The compensated image was recorded on videotape using an ISIT camera. In addition, 48 channels of real-time RTAC data (including deformable mirror drive signals) were digitized and recorded on 9-track tape. When observing the sun, it was found that the image stabilization system worked efficiently even with bad turbulence. However, the expected improvement in image sharpness due to the deformable mirror was obtained only on some occasions and could not generally be predicted, in spite of the fact that the RTAC appeared to operate normally with all feedback loops closed and small residual errors. These results appear to be due to atmospheric parameters, primarily the small size of the isoplanatic patch and the small values of turbulence coherence length during the day. This experiment has confirmed the feasibility of real-time compensation of solar images. However, much work remains to be done to refine the technique.