L.William Bradford (Boeing LTS Inc.), Lewis C. Roberts, Jr.
(The Boeing Company)
Keywords: Atmospherics
Abstract:
We have made measurements with the AEOS Visible Imager camera and with the AEOS adaptive optics wavefront sensor that allow us to estimate the value of Frieds parameter r0 which can be directly related to the seeing. Wavefront sensor slope data is analyzed using Frieds differential angle of arrival equations, and the Visible Imager data is analyzed using the a relationship between the Full Width at Half Maximum of a stars seeing disk and r0. The wavefront sensor data sets will typically have 2000 measurements in 2 seconds. The Visible Imager measurements are about 100 images at intervals of 0.5 to 2 seconds.
We examine the variability and the probability distributions of r0 at multiple time scales. We are particularly interested in how much one measurement may differ from the preceding or the next measurement and in how much that variability varies with the seeing itself. This is of interest to modelers of adaptive optical systems, who in the past relied on models that use fixed values of r0 over the entire time history of a simulation. The data may also prove useful for setting error bounds on image processing algorithms that assume a fixed seeing over a data set. For a very large telescope, the time variability such as we observe is usually then translated into a spatial variability over the aperture, using Taylor’s frozen flow hypothesis. The implication of our data is that that spatial variability must be different than would be found using only a single value of r0 over the full aperture.
Date of Conference: September 12-15, 2007
Track: Atmospherics