The full width of transmission function at half maximum is broadened and the visibility is reduced because of the instrumental linewidth and the periodicityof transmission function.
由于仪器函数的自身线宽及其周期性的加宽作用结果，导致透射函数的半峰值线宽受到加宽，可见度下降。
2
First we employ EMD method to decompose the crude oil prices in NYMEX, and obtain a series of intrinsic mode function (IMF), which are stationary and of strong periodicity, and a trend term.