1. Faculty of Land Resource Engineering, Kunming University of Science and Technology, Kunming 650093, China
2. College of Information Engineering, Qujing Normal University, Qujing 655011, China
3. College of Applied Arts and Science, Beijing Union University, Beijing 100083, China
4. College of Resource and Environment Sciences, Xinjiang University, Urumqi 830046, China
Abstract：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，，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.
Key words：Fractional differential; Mechanism of precision improvement; Pretreatment
[1] Mashimbye Z E, Cho M A, Nell J P, et al. Pedosphere, 2012, 22(5): 640.
[2] WANG Jing-zhe, TASHPOLAT Tiyip, ZHANG Dong(王敬哲, 塔西甫拉提·特依拜, 张 东). Transactions of the Chinese Society for Agricultural Machinery(农业机械学报), 2017, 48(05): 152.
[3] CAO Lei, DING Jian-li, YU Hai-yang(曹 雷, 丁建丽, 于海洋). Transactions of the Chinese Society of Agricultural Engineering(农业工程学报), 2016, 32(3): 101.
[4] ZHANG Dong, TASHPOLAT Tiyip, ZHANG Fei, et al(张 东, 塔西甫拉提·特依拜, 张 飞, 等). Acta Optica Sinica(光学学报), 2016, 36(3): 282.
[5] Zheng Kaiyi, Zhang Xuan, Tong Peijin, et al. Chinese Chemical Letters, 2015, 26: 293.
[6] GU Ji-hong, YU Yuan-jun, KANG De-hua, et al(顾继红, 于媛君, 亢德华, 等). Metallurgical Analysis(冶金分析), 2013, 33(10): 45.
[7] LI Si, BI Chao, DAI Ji-fu, et al（李 斯, 毕 超, 戴继福, 等). Physics Experimentation(物理实验)，2015, 35(1): 42.
[8] WANG Jiao-liang, LONG Li-ping, XIE Dan(王姣亮, 龙立平, 谢 丹). Chinese Journal of Applied Chemistry(应用化学), 2016, 33(7): 841.
[9] LIU Zhi-wei, ZHANG Jun-wei, PENG Qi-jun(刘志维, 张军伟, 彭奇均). Food and Fermentation Industries(食品与发酵工艺), 2012, 38(9): 163.
