KEYWORDS: Instrumentation engineering, Charge-coupled devices, Imaging systems, Signal to noise ratio, Analog electronics, Sensors, Signal processing, Cameras, Polarization, Polarimetry
A CCD imaging system in the Directional Polarimetric Camera is developed, which is comprised of timing driving unit, pro-processing and analog-front-end unit, FPGA main control unit, internal communication and remote measurement unit, image transmission interface unit, and so on. A CCD driving timing method with twice frame transfer and once horizontal readout is proposed to effectively eliminate the residual charge of last frame image and improve the signal-to-noise ratio. The performance of this CCD imaging system is verified. The experimental results show that the 14bit image data can output steadily with a frame frequency of 2.02 frames per second. The imaging signal-to-noise ratio can reach 54.93dB when the CCD is lower than saturated. The dynamic range of the CCD detectable signals is 68.98 dB and the nonlinearity error under different wavelengths is less than 1%. The instrumentation can satisfy the operational requirements such as stable output, excellent linear performance, high signal-to-noise ratio and large dynamic range.
According to the environmental requirement of detectors, we studied the characteristics of Si and InGaAs detectors irradiated by the Cobalt60-γray with the total dose of 5krad, 10 krad, 20 krad, 30krad respectively. We measured the dark current and relative spectral responsivity by the Relative Responsivity Measurement Apparatus before and after irradiation. The results suggest that the characteristics of Silicon and InGaAs detectors don't change obviously after different total dose irradiation, both detectors can work in the space irradiation environment due to its stability and reliability.
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