The field-of-view (FOV) of wide-field telescope is mostly beyond the scope of isoplanatic angle. Though the aberrated wave-front within a limited range close to guide star could be corrected accurately by adaptive-optics (AO) system, the image quality of object region deviation from guide star is dropped severely. The post-processing technique to restore degraded image observed from wide-field telescope is a good compensation for the limit of AO system. Restoration method of space-variant point spread function (PSF) degraded image which are used to overcome the turbulence-induced anisoplanatic effect, can improve image quality in the whole field of view of wide-field telescope, and restore image resolution to optical diffraction-limited level in free space. A multi-frame blind deconvolution restoration algorithm based on image sectioning method is presented here. The image is divided into several subimages, where the PSF of each subimage is assumed to be space-invariant. The conjugate gradient optimization algorithm based on maximum likelihood estimation (MLE) in space domain is adopted to estimate the space-invariant PSF and object information in each block. In order to reduce blocking artifacts at the subregion boundaries, larger, overlapping subregions as well as the Mumford- Shah regularization are used, and then the restored sections are extracted from their center. The resolution of the restored image using 5 satellite model blurred image frames through image sectioning method is enhanced significantly, compared to the space-invariant PSF restoration approach. There are more details about the original object, and it shows the proposed algorithm is valid.
An optically passive athermal infrared optical system working in the 8 - 12 micron long wavelength infrared band was
designed by using a special infrared optical material AMTIR (amorphous material transmitting infrared radiation). The
design principle, design results are described in this paper. In addition, the optical system was incorporated with an
infrared focal plane array forming an infrared camera. The thermal test of imaging quality of this camera is also
presented.
Atmospheric turbulence and telescope aberrations all contribute to image degradation with ground-based telescopes.
For measuring telescope aberrations resulted from atmospheric turbulence, we have developed a method based on phase-diversity
technique. The phase-diversity technique is a novel method for reconstructing the object and the distribution of
wavefront in pupil plane. Using phase-diversity method, we can independently reconstruct many instantaneous
wavefront from pairs of simultaneously recorded focused and defocused images. After that, by averaging these
reconstructed wavefront, the telescope aberrations are separated from dynamic wavefront induced by turbulence. The
simulation of estimation of telescope aberration using phase-diversity method is conducted. The results show the phase-diversity
technique can estimate the telescope aberrations effectively and root-mean-square error is about 0.08
wavelengths.
Cryogenic optical systems are often mounted in vacuum cryostat. An interesting concern in the mechanical design is how to maintain the stability of the line of sight (LOS) of the cryogenic optical system when it is cooled down to very low temperature. To investigate this problem an experimental cryogenic optical system, its mounting structure, and a cryostat were designed and fabricated. After assembling them together, a test experiment for measuring the LOS drift was carried out. Finally, the test results will be presented in this paper.
In this paper, a novel target tracking approach is presented. A scanning mirror has been applied to modulate object and background signal periodically. The object position can be derived by a formula composed of 1st-order and 2nd-order harmonic components obtained form output signals via Fourier transform. Because the field of view of optical system is very small, the radiation from background collected by four cells of quadrant detector doesn't change in short time. The
radiation of background can be suppressed. The result of experiment shows that this tracking approach has a high precision without the influence of the radiation from background and the energy distribution of image spot.
The design of the hybrid athermal CCD camera includes optical and mechanical considerations for minimizing the thermal defocus of the camera. In order to check the thermal characteristic of the athermal CCD camera, a special test was conducted. The CCD camera, its optical and mechanical design, the test setup, and the test results are described.
A new way to evaluate the diffraction efficiency of the diffractive optical element (DOE), which serves as an aberration corrector in an infrared hybrid optical system, is proposed. The directly measured ensquared energy of the hybrid optical system is obtained through an experimental test. Then, the actual line spread function (LSF) of the system under test is measured, and the point spread function (PSF) is calculated from LSF based on the symmetric property of the system. The PSF is used to calculate the so-called derived ensquared energy. The ratio of the directly measured and the derived ensquared energy, defined as the diffraction efficiency of the DOE, represents the fraction of the energy focused onto the image point over the total input energy on the image plane, because the energy loss is caused by the scattering from the DOE corrector. The hybrid optical system, experimental setup, evaluation procedure, and the final results will be presented.
Along with specking imaging characteristic, by wavelet transform, multiresolution for extended object (satellite) speckle imaging is proposed in this paper. Form the simulation, the object feature at different scale is extracted. The satellite features on horizontal and vertical orientation become visible. Only the low-frequency sub-band images are used, the satellite outline is fairly good. Furthermore, for large size images, it may be a method to lessen the computational complexity and compress the images data under the tolerant conditions.
Cryogenic optical system undergoes wide temperature change; therefore it must be athermal. That means when the system is cooled down to very low temperature, its imaging property should be kept as good as at room temperature. One way to achieve athermal optical system requires that all optical and mechanical parts in the system be made from same material. An all-reflective cryogenic optical system was thus developed in IOECAS, in which aluminum alloy was utilized to make such a system. This paper describes the key techniques for manufacturing this cryogenic optical system: material selection, forging process of the aluminum alloy blanks, initial machining, heat treatments, and final figuring. The cryogenic test of the developed system proved the validity of the manufacturing process.
In this paper we describe the design of a reflective/diffractive hybrid optical system, which features no obscuration, imaging system with 100% cold shield efficiency, 4 degrees of field of view, near diffraction limited imaging quality, and working in the long wavelength infrared (LWIR) region of 8 - 12 microns.
An all aluminum reflective optical system was tested to evaluate its optical performances at near liquid nitrogen temperature. A special cryogenic dewar was designed and fabricated with an optical window made of quartz glass on the front wall of the dewar. The optical system under test and a reference plane mirror, which were mounted into the dewar and cooled by liquid nitrogen, formed a double pass interferometric test schema together with a He-Ne interferometer of Fizeau type outside the dewar. The test results showed that there was little differences between the wavefront errors before and after the optical system is cooled, and in both cases the optical system had a diffraction limited imaging quality.
In this paper, we propose a new type of optical baffle with radial leaves, which can effectively reject stray light caused by primary mirror scatter while makes the baffle length shorter than the ordinary one. The stray light test setup for measuring the Point Source Transmittance (PST) of such an optical baffle is described. The test results show that this type of optical baffle can well suppress the stray light from an out-of field light source.
This paper will propose a way to extract target position/range information from the angle-only tracking data with the priori knowledge of the target movement. The target trajectory can be expressed as a function of time, called target function, with n parameters. If m parameters (e.g. target original position, target speed, target acceleration, etc.) are known, or can be estimated to some extent of accuracy, then there remain n-m unknown parameters in the target function. In order to determine these unknown parameters, we should take at least n-m set of tracking data at different times, and construct a system of n-m simultaneous equations. Once all parameters become known by solving this system of equations, the target position and target range can be obtained by substituting the specific time value into the target function. Some typical cases are investigate and the application conditions discussed. Computer simulations are also presented.
KEYWORDS: Digital signal processing, Image processing, Signal processing, Image segmentation, Detection and tracking algorithms, Head, Binary data, Video, Digital imaging, Digital image processing
The extracting of multiple targets in a field of view (FOV) is one of the key problems of the acquisition, tracking, and pointing technique, where a large number of computation and complicated operations must be done. In this paper, a new real- time multiple target centroid extractor is presented. The basic idea is that by using hardware circuit performing image segmentation and horizontal neighborhood analysis, the interesting target pixels are extracted from the raw image, then a digital signal processor carries out the vertical neighborhood analysis of target pixels and calculation of multiple target parameters. An algorithm of target pixels neighborhood analysis is presented for both convex and concave target shapes. A prototype system has been built which can extract parameters of about 100 targets in each FOV, offering centroid and average intensity for each target in the FOV from video signal in real- time.
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