Optical EngineeringReanalysis of turbulence effects on short-exposure passive imaging
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he standard method for modeling the atmospheric short-exposure modulation transfer function (MTF) is due to Fried. This method involves evaluating the impact of amplitude and phase modulations of the propagating wavefront after the removal of the mean wavefront tilt. This tilt is determined by a least-squares analysis. We retain a term involving the correlation between tilt-corrected phase and computed tilt vector that was formerly assumed to be zero. Inclusion of this term yields a new turbulence-strength-dependent effect that degrades performance at high integrated turbulence levels and also predicts super-resolution effects at lower integrated turbulence levels. An analytical approximation is derived from this analysis that describes the new MTF model as a function of three dimensionless parameters related to the angular frequency, system aperture diameter, and integrated turbulence strength.