The Wide Field Survey Telescope (WFST) is a dedicated photometric surveying facility equipped with a 2.5-meter diameter primary mirror, an active optics system, and a mosaic CCD camera with 0.765 gigapixels on the primary focal plane for high quality image capture over a 6.5-square-degree field of view. The mosaic CCD camera is the key device for high precision photometric and high frequency observation and the ‘eye’ of the telescope for deep survey with wide field. The focal plane consists of three kinds of CCD including scientific imaging sensors, wavefront sensors and guiding sensors. In the scientific imaging area, there are 9 back-illuminated full frame scientific CCDs –CCD290-99 from E2V company with pixels of 9K by 9K and pixel size of 10um, which is mosaicked by 3 by 3 with flatness of 20μm PV. The R&D of the camera including the high precision large-scale mosaicking of detectors, detectors’ cryocooling and vacuum sealing, readout and driving with low noise and low power, data acquisition, imaging control, data storage and distribution. Furthermore a camera control system (CCS) was developed at same time.
In low-light-level detection, glow and hot pixels in some imaging sensors become visible due to long-exposure time, leading to image quality degradation. To solve the problem of glow and hot pixels in a single image, an improved extraction algorithm based on the idea of robust principal component analysis is proposed to remove them. The image is divided into three terms in our algorithm: a low-rank matrix (image without glow and hot pixels), an extremely sparse matrix (hot pixels), and a sparse and spatially smooth matrix (glow). Specifically, the total variation norm and ℓ1-norm are exploited to describe the property of glow. Moreover, a top-hat filter and a boundary-searching method are introduced into the soft threshold operator to improve accuracy. The superiority of the proposed approach is demonstrated with evaluations on simulated datasets, quantitative metrics, and real data.
With the development of astronomy, more requirements of low noise and high frame rate are put forward for observation instruments. With the advancement of CMOS technology, scientific CMOS camera can provide excellent quantum efficiency, noise performance, and higher frame rate compared to CCD camera. Based on this, we have designed a scientific CMOS camera with 2K*2K pixels and 11um pixel size. The frame rate of the camera could reach 48fps, with very low readout noise. The structural design, electronic design, cooling method and data processing of the camera will be introduced in this paper.
Earth 2.0 is a Chinese space satellite mission that uses the transit and microlensing methods to search for exoplanets, especially Earth-sized terrestrial planets, including habitable terrestrial planets around sun-like stars. The satellite will work in the halo orbit of the Sun-Earth L2 point for at least 4 years, and is expected to find about 20 Earth like planets in the 4-year observation period. In this paper a CCD camera prototype based on a 4kx4k CCD250 detector for early technology demonstration and high-accuracy photometric performance verification is introduced. The key performance indicators such as readout noise, gain, and linearity of the camera are tested, and the test results will be described.
The wide field survey telescope (WFST) is a new generation survey telescope that is being built in China. Its optical design is a primary-focus system, and its camera is a mosaic charge-coupled device (CCD) camera composed of nine 9 K × 9 K CCD290-99 chips for scientific imaging. A verification platform to test the CCD290-99 chips is designed. The test platform includes a light source system, CCD controller, vacuum Dewar, and refrigerator for cooling the CCD. The CCD controller is a prototype design of the WFST camera that has a high performance, including low readout noise, flexible readout rate configuration, low power dissipation, etc. The digital double correlated sample method is used for video sampling of the CCD’s 16 channels. The specifications of the CCD detector system using a CCD290, such as gain, noise linearity, and crosstalk, are tested using this platform. The test results show that the CCD test platform meets the requirement of the CCD test and the design of CCD controller meets the scientific imaging requirements for the WFST camera.
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