The analytical expressions of the M2-factor for laser beams propagating in oceanic turbulence are derived by using the extended Huygens-Fresnel principle and the definition of the second moment of the Wigner distribution function(WDF). Taking the standard Hermite-Gaussian (SHG) beams and elegant Hermite-Gaussian (EHG) beams as typical examples of laser beams, the propagation properties of the SHG beams and EHG beams in oceanic turbulence are analyzed quantitatively. It is shown that in oceanic turbulence the M2-factor of SHG and EHG beams are different except for beam order m=0 and m=1. At a given propagation distance, the relative M2-factor of SHG and EHG beams in turbulence monotonously decreases with increasing beam order. The relative M2-factor of SHG beams are less than those of EHG beams under the same condition, implying that turbulence influences SHG beams less than EHG beams.
KEYWORDS: Calibration, Cameras, Optical engineering, 3D acquisition, Point spread functions, Platinum, 3D image processing, 3D modeling, Feature extraction, Image processing
When focusing on a long shot, it is very difficult to calibrate a camera with high precision. We propose a method of obtaining a close shot of the calibration plate, extracting corner points from the defocused image of the calibration plate, and constructing a three-dimensional control point to calibrate the camera. We construct a defocused corner template and extract the corner points from the defocused image of the calibration plate using the normalized cross-correlation algorithm. Experimental results show that, after the camera has been calibrated by this method, the average pixel distance accuracy of the re-projected detection point pixel at 40 m reaches 1.9 pixels. The average spatial distance accuracy of the corresponding three-dimensional point reaches 2.1 mm.
A mathematical model of the diffraction efficiency change with the ambient temperature for the double-layer harmonic diffractive elements (HDE) is presented, and its effects are analyzed in this paper. The double-layer HDE structure is investigated and the optimization procedure is based on the equation of diffraction efficiency of the double-layer HDEs. By selecting appropriate design wavelength, the average diffraction efficiency of the system is reaching 99% in working wavelength and working temperature, which improves the image contrast and the image quality significantly. A set of dual-wavelength infrared optical system is designed based on dual-wavelength 320x240 element cooled thermal IR focal plane arrays detector. By introducing double-layer HDEs and aspheric surfaces, the chromatic aberration and the off-axis aberration are well corrected and the system structure is simplified. The system working in the wave band of 3.7~4.8μm and 7.7~9.5μm and with the F number of 2 is consisted of 8 elements and has 100% cold shield efficiency. The image quality evaluating results show that the performance of the dual-wavelength infrared optical system is very well in
temperature from -40C° to +60C°.
Phase unwrapping in regions of abnormal fringes caused by noise, aliasing, fracturing, and the presence of mass discontinuous phases of unwrapped results remains an unresolved issue. We present an approach that combines an iterated discontinuous phase recovery strategy and a quality-guided algorithm based on mutual information quality maps. First, the quality-guided unwrapping algorithm based on mutual information is applied, and the results of the discontinuous phase region are excluded. Second, the remainder of the continuous phase region is rewrapped and unwrapped iteratively until there are no discontinuities in the result. Finally, the discontinuous region is recovered by a continuity operation. The method is validated through both simulations and experiments, thereby demonstrating that the proposed algorithm is robust in the presence of abnormal fringes and that the discontinuous phase can be reduced significantly.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.