<title>Performance of tracking algorithms under airborne turbulence</title>

Abstract

Tracking through a turbulent atmosphere poses several challenging problems. The authors have recently conducted a series of tracking tests at a MIT/Lincoln Laboratories facility where a complete tracking and adaptive optics system is available in a laboratory. The atmosphere is simulated using seven precision rotating phase screens. A great deal has been learned about tracking algorithms and their response under a scintillated atmosphere. Data will be shown to describe a key limitation to high bandwidth tracking. This effect, called the "Optical Frequency", appears to be an upper bound on track bandwidth when using an image based tracking system.

<title>Limitation on the bandwidth of tracking through the atmosphere</title>

“…The second set of tests were mainly concerned with the effects of multiple illumination beams, scintillation and varying bandwidth. This, the second paper on this topic, adds further testing results in support of those presented at AeroSense in 2001 [1].…”

Toward Adaptive Optic Mitigation of Aero-Optic Effects

“…The 1 -G curve and the scaled experimental results agree fairly well. It should be noted that the optical frequency, v/D, defined in Reference [41], is a rough estimate of the 50% cut-off for the two-dimensional aperture, defined earlier, was found to be 0.93 of this value.…”

“…From Eq. (5-51) and figure 41, it seems that performing corrections with a latency phase lag of more than 1.05 radians will add to the OPD rms observed, rather than decrease it. This corresponds to a time lag of about 17% of the time associated with one cycle of the disturbance.…”

“…Boeing, SVS performed a series of tests at the Advanced Concepts Laboratory (ACL) of MIT/Lincoln Laboratory in Lexington, MA, intended to evaluate the effectiveness of various tracking algorithms. [41] This test used a set of moving phase screens to simulate optical turbulence. It should be noted that these screens were constructed with a distribution of phase distortions over a wide range of length scales.…”

“…A value of y 2 = 1 indicates that the tracking signal perfectly follows the disturbances of a given frequency, while lower values indicate lesser degrees of effectiveness. Figure 46 shows Reference [41] results from two of these tests, performed with different relative velocities for the phase screens. They found that these tracking algorithms worked for low frequencies, but not for high frequencies, and the point of transition between these two frequency ranges was dubbed the "optical frequency."…”