Brauers T, Hausmann M, Brandenburger U, Dorn H P
Appl Opt. 1995 Jul 20;34(21):4472-9. doi: 10.1364/AO.34.004472.
Differential optical absorption spectroscopy (DOAS) of atmospheric trace gases requires the detection of optical densities below 0.1%. Photodiode arrays are used more and more as detectors for DOAS because they allow one to record larger spectral intervals simultaneously. This type of optical multichannel analyzer (OMA), however, shows sensitivity differences among the individual photodiodes (pixels), which are of the order of 1%. To correct for this a sensitivity reference spectrum is usually recorded separately from the trace-gas measurements. Because of atmospheric turbulence the illumination of the detector while an atmospheric absorption spectrum is being recorded is different from the conditions during the reference measurement. As a result the sensitivity patterns do not exactly match, and the corrected spectra still show a residual structure that is due to the sensitivity difference. This effect usually limits the detection of optical densities to approximately 3 × 10(-4). A new method for the removal of the sensitivity pattern is presented in this paper: Scanning the spectrometer by small wavelength increments after each readout of the OMA allows one to separate the OMA-fixed pattern and the wavelength-fixed structures (absorption lines). The properties of the new method and its applicability are demonstrated with simulated spectra. Finally, first atmospheric measurements with a laser long-path instrument demonstrate a detection limit of 3 × 10(-5) of a DOAS experiment.
大气痕量气体的差分光学吸收光谱法（DOAS）需要检测低于0.1%的光密度。光电二极管阵列越来越多地被用作DOAS的探测器，因为它们能让人们同时记录更大的光谱区间。然而，这种类型的光学多通道分析仪（OMA）在各个光电二极管（像素）之间显示出约1%量级的灵敏度差异。为了对此进行校正，通常在痕量气体测量之外单独记录一个灵敏度参考光谱。由于大气湍流，在记录大气吸收光谱时探测器的光照与参考测量期间的条件不同。结果，灵敏度模式并不完全匹配，校正后的光谱仍然显示出由于灵敏度差异导致的残余结构。这种效应通常将光密度的检测限制在约3×10⁻⁴。本文提出了一种去除灵敏度模式的新方法：在每次读取OMA之后以小波长增量扫描光谱仪，这能让人们分离出OMA固定模式和波长固定结构（吸收线）。用模拟光谱展示了新方法的特性及其适用性。最后，使用激光长程仪器进行的首次大气测量展示了DOAS实验3×10⁻⁵的检测限。
