Michael Hart, HartSCI LLC; Douglas Hop, HartSCI, LLC; Jeff Richey, Air Force Research Laboratory(AFRL/RD); T. Ryan Swindle, Air Force Research Laboratory(AFRL/RD)
Keywords: Imaging, Adaptive Optics
Abstract:
Current ground-based resolved imaging of resident space objects is mostly limited to dawn and dusk, thus severely restricting the timing of observations. The possibility of daylight imaging represents an advance that would increase utilization of optical telescopes and increase the amount of sky that could be accessed for space surveillance operations. Imaging in full daylight represents a challenge due to the level of atmospheric turbulence noise, high sky background, and the damaging effects of Rayleigh scattering on the signal-to-noise ratio. An important part of overcoming this challenge is the collection of wave-front sensor (WFS) measurements contemporaneous with the focal plane imagery. These measurements are used both to estimate frame-by-frame point-spread functions and to estimate the number and velocities of turbulent layers in a frozen flow model of the atmosphere. This approach, which yields improved estimates of high spatial frequency wave-front errors, is part of the Daylight Object Restoration Algorithm (DORA) currently being implemented at the AEOS 3.6m and SOR 3.5m telescopes.
During daylight, this approach of measuring the wave front using reflected light from the object is limited to the brightest objects in the sky due to the high background noise. A sodium laser guide star (Na-LGS) with a narrow-band filter ahead of the WFS offers a means to overcome the problem. Observations of several objects made in this way were obtained in May 2018 using the 3.5m telescope at SOR with the adaptive optics system operating in closed loop. The WFS measurements from the Na-LGS and independent tip/tilt measurements from the object were analyzed by DORA to estimate the wave fronts after AO correction. Because of the iterative nature of the algorithm, it is able to overcome the focus anisoplanatism associated with LGS. The estimated wave fronts were used by DORA to compute high resolution imagery of space objects during full daylight.
Date of Conference: September 17-20, 2019
Track: Adaptive Optics & Imaging