Fourier and Wavelet Analysis of Water Quality Signals

Taking the nitrogen monitoring data of two sites S1 and S2 in the period 1988-2003 in Baihe River lying Miyun reservoir stream watershed as a case, Fourier and Wavelet analysis were adopted to explore and compare the periodic patterns and temporal pattern characteristics of the two sites. The results showed that the periodic patterns of two sites were discovered using Fourier analysis. The site S1 had a period of two years, while the site S2 had no significant periodic patterns. The temporal pattern characteristics at different scales were obtained through wavelet analysis, which were at small scale for the site S1, while at moderate and small scales for the site S2. The Fourier and wavelet analysis method can both be used in the study of surface water quality temporal change pattern, the first is a coarse method and the latter is a more detailed method for analyzing surface water quality temporal pattern characteristics.