One of the basic parameters of a charge coupled device (CCD) camera is its gain, that is, the number of detected electrons per output Analogue to Digital Unit (ADU). This is normally determined by finding the statistical variances from a series of flat-field exposures with nearly constant levels over substantial areas, and making use of the fact that photon (Poisson) noise has variance equal to the mean. However, when a CCD has been installed in a spectroscopic instrument fed by numerous optical fibres, or with an echelle format, it is no longer possible to obtain illumination that is constant over large areas. Instead of making do with selected small areas, it is shown here that the wide variation of signal level in a spectroscopic ‘flat-field’ can be used to obtain accurate values of the CCD gain, needing only a matched pair of exposures (that differ in their realisation of the noise). Once the gain is known, the CCD readout noise (in electrons) is easily found from a pair of bias frames. Spatial stability of the image in the two flat-fields is important, although correction of minor shifts is shown to be possible, at the expense of further analysis.

中文翻译：

---

光谱平场可用于精密 CCD 增益和噪声测试

电荷耦合器件 (CCD) 相机的基本参数之一是其增益，即每个输出模数单元 (ADU) 检测到的电子数。这通常是通过从一系列平场曝光中找到统计方差来确定的，这些曝光在相当大的区域上具有几乎恒定的水平，并利用光子（泊松）噪声具有等于平均值​​的方差这一事实。然而，当 CCD 安装在由大量光纤馈电或采用阶梯格式的光谱仪器中时，就不再可能在大面积上获得恒定的照明。此处显示，光谱“平场”中信号电平的广泛变化可用于获得 CCD 增益的准确值，而不是只处理选定的小区域，只需要一对匹配的曝光（它们对噪声的实现不同）。一旦增益已知，CCD 读出噪声（在电子中）很容易从一对偏置帧中找到。两个平场中图像的空间稳定性很重要，尽管表明可以校正微小的偏移，但代价是进一步分析。