宽光谱吸收应用中光谱扫描区间的选择

Selection of Scanning Bands for Hyperspectral Absorption Applications

与传统的窄带扫描吸收光谱技术相比,宽光谱吸收技术可以获取更宽光谱范围内的丰富吸收数据,具有很大的技术优势。宽光谱吸收技术测量系统的硬件与传统的可调谐二极管吸收光谱技术测量系统基本一致,唯一不同的是宽光谱吸收技术则使用宽带调谐光源。实际应用中,宽光谱吸收光源一般都具有较宽的光谱覆盖范围(>20 nm),而使用全谱段扫描会对数据采集、存储和处理提出较高的要求,从而增加系统成本和测量工作量。因此,选择合适宽度的光谱扫描区间就成为宽光谱吸收应用中的一个关键问题。利用等效下能级概念,提出了针对宽光谱吸收应用的光谱扫描区间选择的数值方法,并针对1.3μm波段和2μm波段开展了扫描区间选择研究。在1.3μm波段,计算给出的优选扫描谱段与文献报道中使用的谱段相重合,验证了选择方法的可行性和正确性。在2μm波段,在给定工况条件下,通过实验数据验证了所选择扫描区间在温度反演精度方面的优越性。针对实际应用中面临的宽工况环境,通过计算给出了2μm波段优选的扫描光谱区间。计算结果表明,在1.8μm的短波段和1.9μm的长波段均存在适用的光谱扫描区间,其中,1.86μm附近测温精度最高;更宽的扫描带宽有助于降低系统在全光谱范围内的整体测温不确定度。相关研究可为宽光谱吸收技术在燃烧流场诊断的现场应用提供关键技术指导。

Compared with conventional narrow-band-scanning absorption spectroscopy,hyperspectral absorption spectroscopy shows great technical advantages thanks to more abundant absorption information covering a wider spectral range.In practical hyperspectral absorption applications,the laser source can usually be tuned within a wide spectral span(>20 nm).However,full-span tuning puts very high data acquisition,storage,and processing requirements,leading to a high system cost and mammoth workload.Consequently,scanning band selection with proper bandwidth becomes crucial for hyperspectral absorption applications.Here,a numerical method for scanning band selection is developed based on the frequency-dependent lower-state energy.And favourable scanning bands around 1.3 and 2μm wavebands are selected.For the 1.3μm waveband,the selected bands are consistent with those exploited in publications,validating the feasibility and correctness of the method.For the 2μm waveband,the superiority of the selected bands in temperature measurement is verified with experimental data recorded at given operation conditions.Advantageous scanning bands around 2μm are provided concerning the wide operation condition in practical applications.Calculations demonstrate that proper scanning bands exist at the 1.8μm short and 1.9μm long waveband,with the optimum at 1.86μm.A larger scanning bandwidth may not result in the best temperature measurement accuracy,but generally,it brings about a smaller and more controllable uncertainty over the whole spectrum.These findings are instructive for field applications of hyperspectral absorption spectroscopy in engine combustion field diagnosis.