Turbulence mitigation has long been a challenge in long-distance imaging systems. Holographic aperture ladar (HAL), a multiwavelength spatio-temporal heterodyne 3D imaging modality, is also vulnerable to the deleterious effects of volumetric turbulence along the path of propagation. In this work, we develop a sharpness-maximization turbulence mitigation algorithm using a single phase plane approximation to volumetric turbulence. We show preliminary results that simulated HAL fields aberrated by a single turbulent phase screen, coincident with the pupil, are well corrected using this sharpness-maximization algorithm for turbulence profiles with D/r0 values of up to 50.
Holographic Aperture Ladar (HAL) is an intriguing variant of Synthetic Aperture Ladar (SAL). As with
conventional SAL, HAL systems seek to increase cross-range scene resolution by synthesizing a large effective
aperture through the motion of a smaller receiver, and through the subsequent proper phasing and correlation of the
detected signals in post-processing. Unlike in conventional SAL, however, holographic aperture ladar makes use of
a two-dimensional translating sensor array, not simply a translating point detector. In real world applications less
than ideal conditions will be detrimental to final image quality. As the HAL transform requires precise knowledge
of each data collection site in order to properly phase a possibly large collection of coherent sub-images, laser pulse
jitter and system platform vibration are two factors that may result in non-optimum final image quality. To examine
these effects, we first define the following metrics which, in part, quantify final image quality: cross-range
resolution (ΔCR); peak-to-integrated-side-lobe-ratio (PISLR); peak-to-side-lobe-ratio (PSLR); and, pupil plane
RMS wavefront error. We then numerically examine the effects of data collection site uncertainty in a HAL system
via Monte Carlo simulation. In our model we consider only a single point object, though we use otherwise realistic
parameters for sub-aperture diameter, range, wavelength, etc. The effects of positional uncertainty on the image
quality metrics are then calculated, and the results compared to ideal expectations. We will present characteristic
results for several different synthetic aperture diameters and will identify regions of diffraction-limited performance
by considering Marechal's well known λ/14 RMS wavefront error criterion.
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