Atmospheric turbulence correction using digital holographic detection: experimental results

Abstract

The performance of long distance imaging systems is typically degraded by phase errors imparted by atmospheric turbulence. In this paper we apply coherent imaging methods to determine, and remove, these phase errors by digitally processing coherent recordings of the image data. In this manner we are able to remove the effects of atmospheric turbulence without needing a conventional adaptive optical system. Digital holographic detection is used to record the coherent, complex-valued, optical field for a series of atmospheric and object realizations. Correction of atmospheric phase errors is then based on maximizing an image sharpness metric to determine the aberrations present and correct the underlying image. Experimental results that demonstrate image recovery in the presence of turbulence are presented. Results obtained with severe turbulence that gives rise to anisoplanatism are also presented.

Deep-turbulence wavefront sensing using digital-holographic detection in the off-axis image plane recording geometry

“…Eq. (19)]. Note that these image-processing tricks also apply to the results presented in the next section.…”

“…In practice, digitalholographic detection allows for the estimation of the complex field in the presence of an extended noncooperative object via speckle averaging and image sharpening algorithms or the angular diversity created by using multiple transmitters and receivers. [7][8][9][10][11][12][13][14][15][16][17][18] This versatility allows for long-range imaging, 19 three-dimensional imaging, 20 laser radar, 21 and synthetic-aperture imaging. 22 In general, the applications are abundant.…”

Predictive dynamic digital holography

“…Several possible sharpness metrics are listed in Ref. [8], where a typical choice seen in application [26,41] is often,…”

“…Second, extending the Zernike coefficients such that it is able to capture precise spatial structure can compromise the sharpening optimization by a phenomena known as oversharpening [25,26]. Over-sharpening is the result of the sharpening algorithm producing wavefront corrections that drive the final image intensities into star-like structures -that is, when the structure of the USAF bar chart in Fig.…”

“…Earlier works have studied the effects of ROI sharpening [11,25,26]. The increasing attention to localized image sharpening is due to its demonstrated potential in improving image correction distorted by anisoplanatic wavefronts [27].…”