Jianfeng Yang

An improved Fourier-based sub-pixel image registration algorithm for raw image sequence of LASIS

Previous studies indicate that parallel computing for hyperspectral remote sensing synthetic image generation is quite feasible. However, due to the limitation of computing ability within single cluster, one can only generate three bands and a 1000*1000 pixels image in a reasonable time period even using a 40-50 node parallel computing cluster. In this paper, we discuss the capability of using Grid computing where the so-called eScience or cyberinfrastructure is utilized to integrate distributed computing resources to act as a single virtual computer with huge scientific computational abilities and storage spaces. The technique demonstrated in this paper demonstrates the feasibility of a Grid-Enabled Monte Carlo Hyperspectral Synthetic Image Remote Sensing Model (GRID-MCHSIM) for future coastal water quality remote sensing algorithm developments and detection of bottom features and targets in water.

A novel LED lens for rotationally symmetric uniform illumination

Traditional LED (light emitting diode) packaging always adopts hemisphere lens, and can ensure high light output efficiency, but its radiation pattern yields Lambert distribution and is non-uniformity. To enable LED light sources be applied in uniform illumination system, a method to obtain freeform LED lens based on energy equipartition and tangent iteration is proposed. Firstly, according to the Lambertian distribution of LED light intensity and its rotationally symmetric peculiarity, the LED emission angle is divided into N parts in Two-dimensional coordinate system, and the energy contained in each part is equal; Secondly, the target plane is divided into N equal areas along its radii, and the discrete points are corresponding to the N parts of emission angle. So that if the energy in each divided solid angle is controlled to illuminate the equal divided area, the illumination of each corresponding micro-belt on the target plane will be uniform; Finally, to avoid the total reflection of large emission angle rays, the designed lens will refract the rays with 0∼450 emission angle and reflect the rays with 450∼900 emission angle. Choosing an initial point on the freeform generatrix, and using Snell equation and tangent iteration method, the coordinates of all points on the freeform generatrix are obtained, which could be rotated into the freeform surface of the lens. The simulation results using the designed LED lens show that for a rotationally symmetric target plane the illumination uniformity is near to 90% and the energy efficiency is higher than 95%.

Panoramic camera on the Yutu lunar rover of the Chang'e-3 mission

The change-3 panoramic camera, which is composed of two cameras with identical functions, performances and interfaces, is installed on the lunar rover mast. it can acquire 3d images of the lunar surface based on the principle of binocular stereo vision. by rotating and pitching the mast, it can take several photographs of the patrol area. after stitching these images, panoramic images of the scenes will be obtained. thus the topography and geomorphology of the patrol area and the impact crater, as well as the geological structure of the lunar surface, will be analyzed and studied. in addition, it can take color photographs of the lander using the bayer color coding principle. it can observe the working status of the lander by switching between static image mode and dynamic video mode with automatic exposure time. the focal length of the lens on the panoramic camera is 50 mm and the field of view is 19.7 degrees x 14.5 degrees. under the best illumination and viewing conditions, the largest signal-to-noise ratio of the panoramic camera is 44 db. its static modulation transfer function is 0.33. a large number of ground testing experiments and on-orbit imaging results show that the functional interface of the panoramic camera works normally. the image quality of the panoramic camera is satisfactory. all the performance parameters of the panoramic camera satisfy the design requirements.

Light flow model of coded aperture snapshot spectral imager

Coded aperture snapshot spectral imager (CASSI) based on compressed sensing can capture a three-dimensional (3-D) data cube information in one snapshot without scanning, so it is a kind of novel spectral imaging technique with good prospects. In this paper, the data flow procession of two kind of CASSI were studied, which similarities and differences were depicted. The basic principle of the encoded representation of both spectral information and 2-D spatial information of a scene were presented. The numerical estimation techniques based on the compressive sensing theory were applied to reconstruct 3-D data cube.

A sCMOS camera and its tests for focal plane metrology and PSF centroiding experiment

In this paper, the feasibility of a sCMOS camera for astrometric exoplanet detection space mission was evaluated and the evaluation methods were also studied. A 2k x 2k single-chip sCMOS camera was installed on the metrology testbed for the space mission. The pixel size of the detector is 11μm, corresponding to 1.86 arcsec on the focal plane. The sCMOS camera runs with a electronic rolling shutter. We tested the performance of the camera in detail, including the gain, linearity, readout noise, dark current, pixel response non-uniformity, etc.. The data acquisition performance for the pseudo-star and the interference fringes are also studied.

Multispectral image compression algorithm based on spectral clustering and wavelet transform

In this paper, a method based on spectral clustering and the discrete wavelet transform (DWT) is proposed, which is based on the problem of the high degree of space-time redundancy in the current multispectral image compression algorithm. First, the spectral images are grouped by spectral clustering methods, and the clusters of similar heights are grouped together to remove the redundancy of the spectra. Then, wavelet transform and coding of the class representative are performed, and the space redundancy is eliminated, and the difference composition is applied to the Karhunen-Loeve transform (KLT) and wavelet transform. Experimental results show that with JPEG2000 and upon KLT + DWT algorithm, compared with the method has better peak signal-to-noise ratio and compression ratio, and it is suitable for compression of different spectral bands.

Study of imaging fiber bundle coupling technique in IR system

Due to its advantageous imaging characteristic and banding flexibility, imaging fiber bundle can be used for line-plane-switching push-broom infrared imaging. How to precisely couple the fiber bundle in the optics system is the key to get excellent image for transmission. After introducing the basic system composition and structural characteristics of the infrared systems coupled with imaging fiber bundle, this article analysis the coupling efficiency and the design requirements of its relay lenses with the angle of the numerical aperture selecting in the system and cold stop matching of the refrigerant infrared detector. For an actual need, one relay coupling system has been designed with the magnification is -0.6, field of objective height is 4mm, objective numerical aperture is 0.15, which has excellent image quality and enough coupling efficiency. In the end, the push broom imaging experiment is carried out. The results show that the design meets the requirements of light energy efficiency and image quality. This design has a certain reference value for the design of the infrared fiber optical system.

Optomechanical integrated simulation of Mars medium resolution lens with large field of view

The lens of Mars detector is exposed to solar radiation and space temperature for long periods of time during orbit, so that the ambient temperature of the optical system is in a dynamic state. The optical and mechanical change caused by heat will lead to cameras visual axis drift and the wavefront distortion. The surface distortion of the optical lens includes the displacement of the rigid body and the distortion of the surface shape. This paper used the calculation method based on the integrated optomechanical analysis, to explore the impact of thermodynamic load on image quality. Through the analysis software, established a simulation model of the lens structure. The shape distribution and the surface characterization parameters of the lens in some temperature ranges were analyzed and compared. the PV/RMS value, deformation cloud of the lens surface and quality evaluation of imaging was achieved. This simulation has been successfully measured the lens surface shape and shape distribution under the load which is difficult to measure on the experimental conditions. The integrated simulation method of the optical machine can obtain the change of the optical parameters brought by the temperature load. It shows that the application of Integrated analysis has play an important role in guiding the designing the lens.

Thermal effects of optical antenna under the irradiation of laser

The laser communication terminal is a precision optical, mechanical, electrical integration device which operations extremely high accuracy. It is hard to improve the space environment adaptability in the hash vibration, thermal cycling, high vacuum and radiation conditions space environment. Accordingly, the optical antenna will be influenced by space thermal environment. Laser energy will be absorbed when optical antenna under the irradiation of laser. It can contribute to thermal distortion and make the beam quality degradation which affects the performance of laser communications links. This influence will aggravate when the laser power rising.Wavefront aberration is the distance between the ideal reference sphere and the actual distorted wavefront. The smaller the wavefront aberration, the better the optical performance of the optical antenna. On the contrary, the greater the wavefront aberration, the worse the performance of the optical antenna or even affect the normal operation of the optical antenna. The performance index of the optical antenna generally requires the wavefront aberration to be better than λ/20. Due to the different thermal and thermal expansion coefficients of the material, the effect of thermal deformation on the optical antenna can be reduced by matching the appropriate material. While the appropriate support structure and proper heat dissipation design can also reduce the impact. In this paper, the wavefront aberration of the optical antenna is better than λ/50 by the material matching and the appropriate support structure and the secondary design of the diameter of 5mm hole thermal design.

Design of the relay lens for infrared system coupled with imaging fiber bundle

Relay lens is an important element for infrared system coupled with imaging fiber bundle. According to the basic composition and structural characteristics of infrared system coupled with imaging fiber bundle, this paper put forward the general principle and method of its relay lens design, then a material relay lens has been designed by ZEMAX with definite performance index. It has a working spectral coverage from 3.7μm to 4.8μm, focal length of 33.5mm, magnification of -0.6, linear field of view of 12mm, objective numerical aperture of 0.15. It is objective telecentric and is adapted to the relay of infrared detector and imaging fiber bundle. The total lens has two aspheric surfaces and only four pieces of singlet. Its MTF value is 0.7@17 lp/mm, and distortion is -0.19%. After necessary tolerance analysis and structural design, this relay lens has been fabricated. The optical performances fulfill the design requirements and clear images have been got by this lens. These prove the validity and rationality of the design method. It gives a foundational guidance for such relay lens design.