Image quality estimation: pathfinding for the Vera C. Rubin Observatory

The Vera C. Rubin Observatory is nearing completion, and we are embarking on a campaign to optimize the image quality during its upcoming 10-year optical survey. Here, we present the tools and methods we are implementing to disentangle and quantify the different sources of image degradation, as well as our plans to correct and mitigate as many of these different contributions to seeing as possible. The tools include an on-site Differential Image Motion Monitor (DIMM) for measuring atmospheric seeing, multiple 2D and 3D sonic anemometers for measuring in-dome wind speed and turbulence, and direct dome seeing monitors. We also implement a guider mode that allows data to be taken at 9Hz over small regions and a stuttered and streaked imaging mode that allows us to measure mount tracking and jitter and perform atmospheric tomography. Additionally, we use curvature wavefront sensing to estimate the residual wavefront error to support the telescope’s alignment and focus. This is the same algorithm that we will use for the Simonyi Survey Telescope. Many of these tools, as well as additional techniques to quantify the contribution of astigmatism to seeing, have been tested at the Auxiliary Telescope (AuxTel). This 1.2m telescope acts as a pathfinder for the Rubin Observatory. We present initial results and the creation of an image quality budget table for AuxTel to characterize and monitor significant sources of image quality degradation. We then discuss plans for implementing these techniques on the 8.4m Simonyi Survey Telescope.