Research On Technologies Of High Sensitivity And Large Dynamic Range Low Light Level Imaging In Space

The low light level(LLL)remote sensing technology can obtain the characteristics of the target in visible and near infrared band under low illumination,and provide nighttime images with daytime resolution.It has opened a large number of new interdisciplinary research subjects.With the expansion of the application scope of the LLL imaging data and the subdivision of the application field,the demand for high resolution and the large dynamic range of LLL images is becoming more and more intense.Therefore,the higher performance of the LLL imaging system is required,in which low noise and high sensitivity LLL detection technology has become the key technology to further improve the system performance.The sCMOS image sensor has many advantages in the field of LLL detection.Based on the sCMOS image sensor,this thesis has studied the low noise detection technology,the system sensitivity enhancement and evaluation technology and the digital domain TDI LLL imaging technology.The main contents and innovation of the research include:1)The noise characteristics of the sCMOS image sensor LLL imaging system are analyzed,the corresponding noise model is established,and the influence of the system bandwidth on the SNR is deeply analyzed.The optimum system bandwidth is calculated by simulation.In addition,the characteristics of random row stripe noise of LLL imaging system based on sCMOS image sensor are studied and its mechanism is analyzed.The adaptive random row stripe noise correction method in space domain is proposed with the signal readout characteristics of the sensor,and the good correction effect is obtained.2)The calculation method of the pixel by pixel conversion gain of the imaging system is derived,and the error introduced in the calculation process is analyzed.On the basis of the theoretical analysis,the conversion gain of each pixel is measured by single sample and multiple sample points.The results show that the accuracy of pixel conversion gain can be improved by using multiple sample points combined with least square method.The noise characteristics of the system are tested and analyzed,and the SNR model of the system is established.Combined with the simulation and test results,the method of improving the SNR of the system is studied.The theoretical analysis shows that in the case of limited aperture of the optical system,it is necessary to extend the integration time of the space LLL imaging system by using the digital domain TDI imaging mode to improve the SNR.In addition,in view of the problem that the system SNR is difficult to evaluate under the condition of night sky light,a method based on the absolute radiometric calibration of the LLL integration sphere is proposed to calculate the SNR of the system.This method can accurately and objectively evaluate the system SNR performance of the LLL imaging system under the night sky light condition.3)The demand of digital domain TDI imaging mode to image sensor is analyzed.A digital domain TDI data processing method suiTable for engineering application is given.The signal and noise characteristics of the digital domain TDI LLL imaging system are analyzed.The digital domain TDI imaging mode is used to realize the large dynamic range space LLL imaging.The dynamic MTF parameters which lead to the degradation of the system imaging quality by the TDI imaging mode are analyzed,and the adaptation error of the integration stage and the velocity is studied.The relation provides a basis for the design and parameter optimization of TDI imaging system in digital domain.4)A set of LLL imaging system based on sCMOS image sensor is built according to the low noise and high sensitivity LLL detection theory and the method of digital domain TDI imaging mode,and the system noise is tested,and the LLL imaging experiment and the simulated push digital domain TDI LLL imaging experiment are completed.The results show that the LLL imaging system can obtain good quality light image.The digital domain TDI imaging method can improve the SNR and the dynamic range of the LLL image.The image SNR is increased from the 5.04 dB to 19.78 dB with the integration stage of 30,and the dynamic range of the system is improved by 29.54 dB than that of the traditional method.Based on the sCMOS image sensor,this paper studies the low noise and high sensitive imaging technology.Through theoretical analysis and experimental verification,it shows that the digital domain TDI LLL imaging technology of the global shutter sCMOS image sensor can meet the needs of high sensitivity and large dynamic range space LLL imaging,and provides new ideas for the design and implementation of the space LLL imaging system.Finally,the paper puts forward some suggestions for further research.