目前分数阶微分在野外实测光谱中的应用和光谱反演盐渍土盐分的最优波段机理解释尚未见到。 针对传统整数阶微分造成位于分数阶次的光谱信息丢失和模型精度降低的问题。 以新疆阜康市盐渍土盐分和野外光谱为数据源, 对原始光谱及常见4种变换进行0～2阶(阶数间隔取0.1)的共21阶分数阶微分处理, 以探讨盐渍土光谱预处理精度提升的机理。 结果表明: (1)分数阶微分因阶数连续能精确显示出求导中的光谱变换细节, 提升光谱谱峰间的分辨率; 且因阶数增加逐渐改变谱峰的峰形轮廓和去峰形化操作, 导致盐渍土分数阶微分曲线逐渐向曲线斜率的变化率靠近, 即详细刻画出了0阶到一阶微分和斜率与曲率间的细微差异。 (2)五种光谱变换的分数阶微分值与含盐量的相关系数, 通过0.01显著性水平检验, 且大于整数阶(1阶、 2阶)的相关系数最大绝对值的, 主要集中在1.3, 1.4, 1.5阶。 其中, 1.4阶1/lgR和1.3阶1/R的相关系数提升百分比最大, 分别为12.78%和13.03%。 (3)不论何种光谱变换, 各分数阶微分值与含盐量最大相关系数对应的波段均出现在598 nm(1/R)和618 nm(R, R, 1/lgR和lgR), 且均在1.3或1.4阶。 (4)研究区Na+占阳离子总量的65.74%, 与总盐的相关性达0.738, 钠原子的主要谱线是589.3 nm是造成各种光谱变换与土壤含盐量相关性最佳的波段位于598和618 nm最主要的原因。

Currently the application of fractional differential (FD) algorithm for field spectra and the optimal band mechanism of spectra inversion salt in saline soil has not been seen. In view of the problem that traditional integer-order differential algorithm causes fractional-order spectral information lose and model accuracy decrease the salinity and field spectra of saline soils in Fukang City of Xinjiang, China, were taken as data sources and original spectrum and common four transforms were subjected to a total of 21-order FDbetween 0～2 orders (interval is 0.1), in order to explore the mechanism improvement of pretreatment precision for saline soil spectra. Results showed that: (1) FD could accurately display the details of spectral transformation in the derivation process due to continuous orders, and improve the resolution between peaks of the spectra. Italso gradually changed peak shape and removed peaking operationdue to the increase of orders, which resulted in the gradual change of FD curve of saline soil to the slope of the curve, namely, a detailed description of subtle differences from 0-order to slope and between slope and curvature. (2) Correlation coefficient (CC) between FD value and salt content of five spectral transforms was tested by 0.01 significance level, and max CC absolute larger than integer order (1-order, 2-order) was mainly concentrated at 1.3, 1.4, 1.5 orders. Among them, CC of 1.4 order 1/lgR and 1.3 order 1/R had the largest increase percentage, which were 12.78% and 13.03%, respectively. (3) Regardless of the spectral transformation, the corresponding bands for max CC between salt content and all FD value appeared at 598 nm (1/R) and 618 nm (R, R, 1/lgR and lgR), and they were all in 1.3 or 1.4 order. (4) Na+ accounted for 65.74% of total cations, and its correlation with total salt was 0.738. The 589.3 nm spectrum was the main reason why the bands with the best correlation between various spectral transforms and soil salinity were located at 598 and 618 nm.