基于光纤探头的洋葱近红外光谱检测的数值模拟
Numerical simulation of NIR spectroscopy measurement of onion bulbs using fiber probes

利用Monte Carlo方法模拟光在洋葱组织内部的传输特性，并结合采用光纤探头的接触式测量条件，对漫反射检测信号进行仿真计算，分析表皮厚度和光学性质对测量的影响。结果表明，表皮对信号强度有明显的衰减作用，但对平均穿透深度影响不大。在波长800 nm处，探测点到入射点的距离（源探距）为0.9～2.0 cm时，在保证信号强度的同时可达到0.5～0.8 cm的平均穿透深度，并可检测到此深度的颈腐病害(Botrytis allii Munn.)；使用直径和数值孔径较大的光纤探头可以在保证测量精度的同时提高探测灵敏度。
Near infrared spectroscopy technique is widely used to nondestructively inspect agricultural products. The Monte Carlo method was used to simulate light propagation in onion bulbs. The measurement system using fiber probes was modeled. The detected diffuse reflectance signals were calculated and the effects of dry skins on the measurements were analyzed. The results showed that the dry skin reduced the signal strength detected, but had little influence on the average penetration depth. At the wavelength of 800 nm, a source detector separation between 0.9 and 2.0 cm is preferred to reach an average penetration depth of 0.5 to 0.8 cm and is capable of detecting the neck rot infected flesh located in this depth. Using fiber probes with lager acceptance radii and numerical apertures helps increase the measurement sensitivity.