4.2. Smoothed time profile of EVI
The smoothed time profiles of EVI generated by both transforms are shown in Fig. 6. These time profiles show the same seasonal tendency as the original EVI data. The changes around the planting season in the second derivative of time profiles of the EVI generated by wavelet transform are larger than those by Fourier transform. The dates of the minimal and inflection points differed between profiles from wavelet and Fourier transforms (Fig. 6). In addition, local changes in the time component around the planting season were blurred in the Fourier transform (Fig. 6). The Fourier transform inadequately represents the appropriate position of the minimal and inflection points in the time domain. In the filtering process, the wavelet transform can hold the time component of temporal EVI data, but the Fourier transform cannot. We assumed that these characteristics of the time component in temporal EVI data led to the difference in accuracy. We believe that the filtering method using the wavelet transform is much more sensitive to vegetation seasonal changes than that using the Fourier transform