Abstract
For high-speed aircraft, a conformal window is used to optimize the aerodynamic performance. However, the local shape of the conformal window leads to large amounts of dynamic aberrations varying with look angle. In this paper, deformable mirror (DM) and model-based wavefront sensorless adaptive optics (WSLAO) are used for dynamic aberration correction of an infrared remote sensor equipped with a conformal window and scanning mirror. In model-based WSLAO, aberration is captured using Lukosz mode, and we use the low spatial frequency content of the image spectral density as the metric function. Simulations show that aberrations induced by the conformal window are dominated by some low-order Lukosz modes. To optimize the dynamic correction, we can only correct dominant Lukosz modes and the image size can be minimized to reduce the time required to compute the metric function. In our experiment, a 37-channel DM is used to mimic the dynamic aberration of conformal window with scanning rate of 10 degrees per second. A 52-channel DM is used for correction. For a 128 × 128 image, the mean value of image sharpness during dynamic correction is 1.436 × 10−5 in optimized correction and is 1.427 × 10−5 in un-optimized correction. We also demonstrated that model-based WSLAO can achieve convergence two times faster than traditional stochastic parallel gradient descent (SPGD) method.
Highlights
Targeting and sensing on airborne platforms is mostly realized by imaging through a spherical or flat window
A 52-channel deformable mirror (DM) is used for correction
We demonstrated that model-based wavefront sensorless adaptive optics (WSLAO) can achieve convergence two times faster than traditional stochastic parallel gradient descent (SPGD) method
Summary
Targeting and sensing on airborne platforms is mostly realized by imaging through a spherical or flat window. Classical AO uses a wavefront sensor to measure aberration and a DM to make conjugated correction. A dedicated wavefront sensor is omitted in WSLAO and the control signal of DM is derived from the intensity information on the image detector. The choice of mode is based on the model used to describe the mathematical relationship between modal coefficients and metric function. Model-based WSLAO can achieve convergence much faster than model-free algorithms and avoid dropping into local optima, which are both crucial for dynamic aberration correction. The model-based WSLAO must be calibrated before correction in order for the DM to generate a specific mode, which is not required in model-free algorithm like SPGD. Model-based WSLAO is applied for correction of dynamic aberration induced by conformal window of an infrared remote sensor on high-speed aircraft. Numerical simulations and experiments are made to demonstrate the feasibility and performance of our method
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