Since the concept of wavefront coding was proposed, many types of phase masks have been reported to extend the depth-of-field of imaging system. Unfortunately there exist some unpleasant image artifacts in the final decoded images, especially for asymmetric phas1 e masks. In this paper, we illustrate a technique that involve shifting a phase mask laterally in pupil plane to introduce axial defocus to an imaging system, which can further be used to determine the defocus map according to the amount of image artifacts. This eventually enables recovery of extended depth-of-filed, artifacts-free decoded images together with a range map. Theoretical analyses and experimental results indicate the effectiveness of this method. Keywords: wavefront coding,
In order to avoid the resonance between the two dimensional turntable and the satellite, the modal simulation of the two dimensional turntable is carried out in this paper. And the simulation results are compared with the experimental results, combined with modal experiment, the simulation results before and after optimization are further verified. Firstly, two dimensional turntable as the research object in this paper, and it is modeled with the finite element method, then we use Patran/Nastran to conduct the modal simulation. In the modal simulation process, the bearing can be equivalent to the spring element, and the MPC element is used to instead of the spring element. And we introduce the modeling method of the MPC unit, the fundamental frequency of two dimensional turntable is obtained through modal simulation. At last, the model experiment is verified by hammering method, the frequency response functions in each direction of x, y and z are measured. Simulations and experimental results show: after optimization, the fundamental frequency of the two dimensional turntable is 42 Hz, which is higher than that of the base frequency 25 Hz, illustrating that the optimized structural design of the two dimensional turntable meets the requirements; The natural frequency and the experimental errors of three - dimensional turntable in x, y, z are 5%, which shows that MPC can simulate the bearing accurately, and is suitable for the simulation of two dimensional turntable.
As the atmospheric environments get more complex, the surface characteristics are diverse, spaceborne remote sensing cameras with the characteristics of large aperture, long focal length, and small size are demanded ever-increasing, and the high-sensitivity photoelectric detectors are required to detect more observing targets, the nonlinear process of remote sensing imaging system is worth consideration. In this paper, time delay integrated charge-coupled device (TDICCD) is used as an example to analyze imaging chains of space remote sensing system at visible wavelengths. The nonlinear process influenced by atmospheric radiation transmission mode, the reflection characteristics of earth surface, ground-air couping effect, imaging optical system, TDICCD photoelectric detector, imaging electronics system, data transmission/compression system, and ground station system is researched in detail. At the same time, the method to reduce the nonlinear effects of the image is discussed. In order to apply the space remote sensing information to all walks of life effectively, the nonlinear process will be improved by high-precision atmospheric radiation transmission calculation, reducing the move of the image plane and the noise of the electronics system, designing the A/D converter with stable gain coefficient, optimizing the compression/decompression process, and reducing information loss of the remote sensing imaging system from satellite to the ground station system.
Images will be blurred by relative motion between the camera and the object of interest. In this paper, we analyzed the process of motion-blurred image, and demonstrated a restoration method based on Lucy-Richardson algorithm. The blur extent and angle can be estimated by Radon transform algorithm and auto-correlation function, respectively, and then the point spread function (PSF) of the motion-blurred image can be obtained. Thus with the help of the obtained PSF, the Lucy-Richardson restoration algorithm is used for experimental analysis on the motion-blurred images that have different blur extents, spatial resolutions and signal-to-noise ratios (SNR’s). Further, its effectiveness is also evaluated by structural similarity (SSIM). Further studies show that, at first, for the image with a spatial frequency of 0.2 per pixel, the modulation transfer function (MTF) of the restored images can maintains above 0.7 when the blur extent is no bigger than 13 pixels. That means the method compensates low frequency information of the image, while attenuates high frequency information. At second, we fund that the method is more effective on condition that the product of the blur extent and spatial frequency is smaller than 3.75. Finally, the Lucy-Richardson algorithm is found insensitive to the Gaussian noise (of which the variance is not bigger than 0.1) by calculating the MTF of the restored image.
Proc. SPIE. 9142, Selected Papers from Conferences of the Photoelectronic Technology Committee of the Chinese Society of Astronautics: Optical Imaging, Remote Sensing, and Laser-Matter Interaction 2013
The photoelectric rotary and angle encoder is a digital angle measuring device, which is integrated with optics, mechanics and electrics. Because of its simple structure, high resolution, and high accuracy, it has been widely used in precision measurement of angle, digital control and digital display system. With the needs of fast tracking and accurate orientation on the horizon and air targets, putting forward higher requirements on accuracy of angle measurement and resolution of photoelectric rotary and angle encoder. Influences of manufacturing, electronics segmentation, optical and mechanical structure and eccentric shaft to photoelectric encoder precision and reducing methods are introduced. Focusing on the eccentricity error, building up an error correction model to improve the resolution of angle encoder and the model was verified by test.