Dalei Yao

Study on Modeling and Simulation of LEO Satellite’s Optical Reflection Characteristic Based on Davies Bidirectional Reflection Distribution Function

Based on background radiation, material properties, orbit parameters, and the relative motion between LEO satellite body and solar panel, Davies-BRDF (bidirectional reflection distribution function) was used to establish the mathematical models of spectral and imaging characteristic of LEO satellite and calculate the satellite irradiance on entrance pupil and image plane of detector. Here, the surface of LEO satellite was divided into areas and each area was divided into grids. According to the orbit parameters of LEO satellite and detector, imaging condition of LEO satellite was analyzed and the judgment basis of imaging angle and scale was given. Taking different materials and shapes of satellites for example, these input parameters (the properties of structure, materials and orbit) were used to calculate the reflected radiation of every grid of satellite surface, and establish the mathematical models of reflection characteristic. The body coordinate of satellite was set and the relative positions of satellite, background radiation and detector were determined making use of coordinate conversion. In this paper, the imaging degrading effects were taken into consideration in the process of simulation. Simulated results of the satellite optical characteristic were decided by the relative position of the solar, the earth and the LEO satellite, as well as its geometrical shapes, flight figure and surface materials. The imaging results demonstrate that Davies-BRDF can simulate the reflection characteristics of the LEO satellite precisely and the simulated images was more accurate.

Measuring dispersed spot of positioning CMOS camera from star image quantitative interpretation based on a bivariate-error least squares curve fitting algorithm

For a positioning CMOS camera, we put forward a system which can measure quantitatively dispersed spot parameters and the degree of energy concentration of certain optical system. Based on this method, the detection capability of the positioning CMOS camera can be verified. The measuring method contains some key instruments, such as 550mm collimator, 0.2mm star point, turntable and a positioning CMOS camera. Firstly, the definition of dispersed spot parameters is introduced. Then, the steps of measuring dispersed spot parameters are listed. The energy center of dispersed spot is calculated using centroid algorithm, and then a bivariate-error least squares curve Gaussian fitting method is presented to fit dispersion spot energy distribution curve. Finally, the connected region shaped by the energy contour of the defocused spots is analyzed. The diameter equal to the area which is 80% of the total energy of defocused spots and the energy percentage to the 3×3 central area of the image size are both calculated. The experimental results show that 80% of the total energy of defocused spots is concentrated in the diameter of the inner circle of 15μm, and the percentage to the 3×3 pixels central area can achieve 80% and even higher. Therefore, the method meets the needs of the optical systems in positioning CMOS camera for the imaging quality control.

Space debris detection in optical image sequences

We present a high-accuracy, low false-alarm rate, and low computational-cost methodology for removing stars and noise and detecting space debris with low signal-to-noise ratio (SNR) in optical image sequences. First, time-index filtering and bright star intensity enhancement are implemented to remove stars and noise effectively. Then, a multistage quasi-hypothesis-testing method is proposed to detect the pieces of space debris with continuous and discontinuous trajectories. For this purpose, a time-index image is defined and generated. Experimental results show that the proposed method can detect space debris effectively without any false alarms. When the SNR is higher than or equal to 1.5, the detection probability can reach 100%, and when the SNR is as low as 1.3, 1.2, and 1, it can still achieve 99%, 97%, and 85% detection probabilities, respectively. Additionally, two large sets of image sequences are tested to show that the proposed method performs stably and effectively.

Design of a multifunction astronomical CCD camera

To satisfy the requirement of the astronomical observation, a novel timing sequence of frame transfer CCD is proposed. The multiple functions such as the adjustments of work pattern, exposure time and frame frequency are achieved. There are four work patterns: normal, standby, zero exposure and test. The adjustment of exposure time can set multiple exposure time according to the astronomical observation. The fame frequency can be adjusted when dark target is imaged and the maximum exposure time cannot satisfy the requirement. On the design of the video processing, offset correction and adjustment of multiple gains are proposed. Offset correction is used for eliminating the fixed pattern noise of CCD. Three gains pattern can improve the signal to noise ratio of astronomical observation. Finally, the images in different situations are collected and the system readout noise is calculated. The calculation results show that the designs in this paper are practicable.

The digital simulation of end-to-end imaging chain in optical remote sensing system based on MTF models

The conflicts between the miniaturization of optical remote sensor and the high resolution force us to build an end-to-end simulation system, and optimize the process of the image acquisition and processing. In this paper, based on the analysis of MTF models of each link in imaging chain, a scientific visualization method of end-to-end optical remote sensing process using MTF models is presented. And, imaging simulation software is programmed with Matlab to implement the process. Using this program, the final simulated image can be generated from the original through the whole remote sensing image course according to the input parameters of each link in image chain. Through research on simulated images, we can analyze effectively the effects of each link on the quality of images, and carry out the optimization of optical remote sensor.

Maximum projection and velocity estimation algorithm for small moving target detection in space surveillance

The article presents a new method to detect small moving targets in space surveillance. Image sequences are processed to detect and track targets under the assumption that the data samples are spatially registered. Maximum value projection and normalization are performed to reduce the data samples and eliminate the background clutter. Targets are then detected through connected component analysis. The velocities of the targets are estimated by centroid localization and least squares regression. The estimated velocities are utilized to track the targets. A sliding neighborhood operation is performed prior to target detection to significantly reduce the computation while preserving as much target information as possible. Actual data samples are acquired to test the proposed method. Experimental results show that the method can efficiently detect small moving targets and track their traces accurately. The centroid locating precision and tracking accuracy of the method are within a pixel.

Noise model and simulation analysis of the low noise pre-amplifier of CCD camera

The low noise video process chain design is the important guarantee of realization of CCD detection performance. While pre-amplifier locate in the front end of the video signal process of CCD camera, so the low noise preamplifier design is the important guarantee of realization of low noise CCD camera. Firstly, calculate the bandwidth and equivalent noise bandwidth of video process chain of CCD camera. Secondly, design the preamplifier circuit and build the noise model of the preamplifier. Thirdly, according to the noise model calculation the noise of the pre-amplifier. Lastly, build the noise simulation model of the preamplifier. Through theoretical calculation and PSPICE simulation result predict the noise level of the preamplifier of the CCD .The noise level of the preamplifier less than 2 electronics, it meets specification requirement.