Desheng Wen

The progress of sub-pixel imaging methods

This paper reviews the Sub-pixel imaging technology principles, characteristics, the current development status at home and abroad and the latest research developments. As Sub-pixel imaging technology has achieved the advantages of high resolution of optical remote sensor, flexible working ways and being miniaturized with no moving parts. The imaging system is suitable for the application of space remote sensor. Its application prospect is very extensive. It is quite possible to be the research development direction of future space optical remote sensing technology.

Novel subpixel imaging system with linear CCD sensors

Subpixel imaging is one of the effective ways to increase spatial resolutions of optical imagers by reducing frequency aliasing caused by the sampling process of discrete sensor grid. This paper presents a novel subpixel imaging system with linear CCD sensors. The system is consisted of a specially designed focal-plane-assembly(FPA) with two 2048 pixel linear CCD, a CPLD(Complex-Programmable-Logic-Device)-based controller, analog signal chain, and related image processing software. Firstly, analysis of the relationship between MTF and subpixel displacement is conducted, with quantum results presented, and the design of the FPA are analyzed. Secondly, we reviewed related image deconvolution algorithms, and discussed the precision image registration and improved Wiener filtering algorithm for this system, potentials of wavelet-based image restoration are also invoked. Preliminary pushbroom tests of a prototype subpixel imaging system show that the resolution of the subpixel system is 1.5~1.6 times greater than that of conventional system at Nyquist frequency, considerable resolution improvment has been obtained.

A modified star map identification method suitable for astronomical camera

High accuracy star map identification results are the basis of astronomical positioning. The traditional triangle star identification algorithm has a higher redundancy and a poor robustness to noise. Considering the specific requirements of the star map identification of the astronomical camera, in allusion to this default, proceeding with selection of guide stars, construction of guide star catalogue and realization of matching algorithm, a modified triangle algorithm based on traditional one is presented. With the proposed algorithm, the guide star is selected from astronomical durchmusterung. In order to speed up guide star indexing, the guide star catalogue is founded after dividing the sky using the overlapping rectangle method. The guide star sub-catalogue is constructed by the radius of guide triangle circumcircle and the two sides of guide triangle. The characteristic radius is used for indexing and sorted in an ascending order to improve the searching efficiency in the processing of star map identification. The matching scope of the angular distance is narrowed and the matching rate of angular distance is improved by the matching of the characteristics radius. If there exists redundancy, a normalized magnitude is used to eliminate it. Within the observing area of the real sky, the 1050 star maps continuously are calculated. The simulation results show that, the identification rate of this algorithm is greater than 97. 83% when the noise of position error is two pixels, and the average identification time is about 25. 07ms. Compared with the traditional triangle algorithm, this modified algorithm has a couple of advantages, including the smaller storage capacity of guide star catalogue, better robustness to position and magnitude error, higher rate of correcting star map identification and lower redundancy.

Subpixel imaging technique

The subpixel imaging system with line-array CCD sensors and with area-array CCD sensors are introduced in the past paper. The system is consisted of a high-resolution lens, a beam splitter and two line-array CCD sensors or four area- array CCD sensor with subpixel displacements in the focal planes. In order to get a high spatial resolution in the pushbroom direction for pushbroom imaging system, the sample spacing between line images is decreased. Processing the original images got through the subpixel imagin system specially, a new image with higher spatial resolution could be constructed. The imaging system will be suitable for space application because the configuration is stable and rugged. The key techniques involved in the subpixel imagin system are the following: (1) the precision measuring technique of the CCD sensors location and (2) the technique of the new image constructing.

A novel design of subminiature star sensor's imaging system based on TMS320DM3730

Development of the next generation star sensor is tending to miniaturization, low cost and low power consumption, so the imaging system based on FPGA in the past could not meet its developing requirements. A novel design of digital imaging system is discussed in this paper. Combined with the MT9P031 CMOS image sensor’s timing sequence and working mode, the sensor driving circuit and image data memory circuit were implemented with the main control unit TMS320DM3730. In order to make the hardware system has the advantage of small size and light weight, the hardware adopted miniaturization design. The software simulation and experimental results demonstrated that the designed imaging system was reasonable, the function of tunable integration time and selectable window readout modes were realized. The communication with computer was exact. The system has the advantage of the powerful image processing, small-size, compact, stable, reliable and low power consumption. The whole system volume is 40 mm *40 mm *40mm,the system weight is 105g, the system power consumption is lower than 1w. This design provided a feasible solution for the realization of the subminiature star sensor’s imaging system.

Design of imaging circuitry of space CCD camera based on FPGA

A imaging system of area-array CCD cameras based on FPGA was designed. The overall structure and design of the system was introduced in detail. According to the working mode and driving timing requirements of this CCD image sensor, the driving schedule under the control of FPGA was designed. The working mode and parameters of such an imaging system were aligned with the control signals in accordance with the general requirements of space CCD cameras. With FPGA device as the platform of hardware design, the hardware of integrated timing and control system was described in VHDL language. The A/D converter AD9945 based on the correlated double sampling was used to realize the analog-digital (A/D) conversion of ICX285AL output signals. The XQR2V3000-4CG717V developed by Xilinx was chosen to accomplish the design of this hardware circuit. Through simulation, the correctness of driving schedule was verified, thus preparing necessary hardware for the final development of space area-array CCD cameras with high performance.

Optical system design of descent camera

This paper presents two optical systems of descent cameras. These two lens systems have the same parameter whose effective focal length is 14 mm, F-number is F/8, field of view is 72 degree and the working wavelength rang is 0.5-0.8μm. Two different optical structures were used respectively in these two systems. This paper analyses and compares their capacity respectively. Only two kinds of glass material were used in these two optical systems, the difference from the usual imaging system is that this system is required to be fit for the demand of spaceflight environment. It should be small and light enough on the one hand, and the imaging quality should be high on the other hand. The detector whose image element size is 14 um, its Nyquist cut-off frequency is 35.711p/mm, its diffraction limit MTF is 0.76. Program 1s 1.0 field MTF≥0.58 at the Nyquist cut-off frequency. The biggest relative distortion of this system is+0.2%, Image irradiance at the edge of the field was found to be 50% of the central value. In the design of program 2, MTF approach diffraction limit, the biggest relative distortion in 1.0 field is 0.7%. Because of the structure of telecentric beam path design, the relative illumination in 72° view field is comparatively average.

Novel pushbroom imaging system

A novel superresolution imaging system with line-array CCD sensor is introduced in the paper. The system is consisted of a high resolution lens, the beam splitter and two line- array CCD sensors. The two same line-array CCD sensor which the pixel size is b micrometers by b micrometers are set up in the two imaging planes of the imaging systems and their central coordinates are respectively (0,0) and (b/2, 0). In order to get the high spatial resolution along the pushbroom direction, the sample spacing between line images is decreased. The line array is moved only half a pixel width instead of a full pixel width for each line image scan. Two different images would be simultaneously got through the novel linear pushbroom imaging system for the moving scenes. Processing specially, a new image with higher spatial resolution than the original two images would be obtained. The novel imaging system will be suitable for space application because the configuration is stable and rugged. If the new method is used in the design of remote sensing payloads to perform. Earth observation, the focal length of the new remote sensing system could be reduced about 50 percent keeping the same spatial resolution comparing with the traditional imaging system. If the sensor is area-array CCD in the imaging system, the superresolution imaging system would be consisted of a high resolution lens, the beam splitter and four area-array CCD sensors with subpixel displacements in the focal planes.