基于电子倍增的高光谱成像链模型的系统信噪比分析

System Signal-to-Noise Ratio Analysis of Hyperspectral Imaging Chain Model Based on Electron Multiplication

高光谱成像的应用效果非常依赖于所获取的图像信噪比(SNR)。在高空间分辨率下,帧速率高、信噪比低,由于光谱成像包含了两维空间-光谱信息,不能使用时间延迟积分(TDI)模式解决光能量弱的问题;目前多采用摆镜降低应用要求,但增加了体积和质量,获取的图像不连续,且运动部件降低了航天的可靠性。基于此,将超高速电子倍增与成像光谱有机结合,构建了基于电子倍增的高分辨率高光谱成像链模型,综合考虑辐射源、地物光谱反射、大气辐射传输、光学系统成像、分光元件特性、探测器光谱响应和相机噪声等各个环节,可用于成像链路信噪比的完整分析。采用LOWTRAN 7软件进行大气辐射传输计算,对不同太阳高度角和地物反射率计算像面的照度,根据电子倍增电荷耦合器件(EMCCD)探测器的噪声模型,计算出不同工作条件下的SNR。对SNR的分析和实验,选择适当的电子倍增增益,可使微弱光谱信号SNR提高6倍。

The application effect of hyperspectral imaging relies heavily on the acquired signal-to-noise ratio （SNR） of images. The hyperspectral imaging requires a high frame rate and a low SNR for a high spatial resolution. The time-delay-integration （TDI） mode cannot he used to solve the problem of weak light energy, because the spectral imaging contains the two-dimensional spatial-spectral information. A swing mirror is usually used to reduce the application requirement. However, not only the volume and weight increase, but also the acquired image is discontinuous and the space reliability of the moving parts is reduced. Thus the ultra-high speed electron multiplication and the imaging spectroscopy are combined organically, and a high-resolution hyperspectral imaging chain model based on electron multiplication is built. This model can be used for a complete analysis of the SNR in an imaging chain, if all elements such as radiation source, object reflectance, atmospheric radiation transmission, optical system imaging, spectroscopic characteristics, detection spectral response and camera noise are comprehensively considered. The LOWTRAN 7 software is used to investigate the atmospheric radiation transmission. The illuminance at the image plane is calculated for different solar altitudes and object reflectance, and the SNR under different working conditions is calculated according to the noise model of an electron multiplying charge coupled device （EMCCD） detector. Through the analysis and experiment of SNR, a suitable choice of multiplication gain can make the SNR of weak spectral signals enhanced by 6 times.