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摘要: 为了对作物进行更灵敏、更高效的生长监测，国内外相继设计了各类高光谱分辨率的光谱仪用来探测叶绿素荧光效率。本文对传统Offner光谱仪系统进行改进，得到了光谱分辨率更高的整体结构。光学系统选用双反望远系统，光谱仪部分采用高刻线密度反射型凸面光栅，实现更高的光谱分辨率。在此基础上，添加放大透镜以满足长狭缝需求，同时得到了一种狭缝-像面在光栅同一侧的Offner结构。利用codeV软件对望远系统和光谱仪部分的初始结构进行优化。结果表明，工作在670~780 nm波段时，光谱分辨率为0.3 nm，在17 lp/mm截止频率下整体调制传递函数MTF>0.75，各视场条件下弥散斑均方根半径RMS<15 μm。由此可知，该方法可以满足作物生长叶绿素监测领域的高精度、实时性要求。
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关键词:
- 光学设计 /
- Offner光谱成像系统 /
- 超高光谱分辨率
Abstract: To monitor crop growth more efficiently, various kinds of hyperspectral spectrometers have been designed to detect chlorophyll fluorescence. In this paper, the traditional Offner spectrometer system is improved, and a structure with a higher spectral resolution is obtained. The double-reflection telescope system is selected, and the spectrometer adopts a highly dense linear reflective convex grating to achieve higher spectral resolution. On this basis, an amplifying lens is added to meet the need for a long slit. An Offner structure is obtained with a slit and image plane on the same side of the grating. The initial structure of the telescope system and the spectrometer are optimized by codeV software. The results show that the spectral resolution is 0.3 nm in the range of 670~780 nm, the overall Modulation Transfer Function (MTF) is greater than 0.75 at the cut-off frequency of 17 lp/mm, and the Root Mean Square radius (RMS) of the speckle is less than 15 μm. The proposed system can meet the requirements of highly precise real-time monitoring in crop growth chlorophyll detection. -
图 9 各波段RMS点列图
Figure 9. RMS point diagrams at different wavelengths (λ=670、725、780 nm)
图 12 各波段整体结构MTF曲线图
Figure 12. MTF curves of the system at different wavelengths (λ=670、725、780 nm)
图 13 各波段整体结构RMS点列图
Figure 13. RMS point diagrams of the system at different wavelengths (λ=670、725、780 nm)
图 14 整体结构径向能量分布图
Figure 14. Radial energy distributions of the system at different wavelengths (λ=670、725、780 nm)
表 1 超高光谱分辨率改进型Offner光谱仪各项指标
Table 1. Indexes of an improved Offner spectrometer with ultra high spectral resolution
项目 指标 探测高度/km 810 光谱分辨率/nm 0.3 工作波长/nm 670~780 焦距/mm 240 入瞳直径/mm 75 半视场(°) x：4，y：20 调制传函（MTF） >0.75 (17 lp/mm) 弥散斑均方根半径（RMS）/μm <15 
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表 2 GSENSE4040BSI探测器指标
Table 2. Detector parameters of GSENSE4040BSI
项目 参数 分辨率 4096×4096 像元尺寸/μm 9×9 感光面积/mm 36.8×36.8 照明方式 背照明 帧频(frame·s−1) 24
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