**2. Method**

Periodic noise is recurring in raw seismic data, and its amplitude is constant within the recording time [6]. Based on these characteristics, we can differentiate and estimate periodic noise from ambient noise. Because ambient noise, such as periodic noise, white Gaussian noise and other non-stationary [1,18] random noise, is ubiquitous in seismic records before the first arrivals, we can extract noise features and construct the noise dictionary from it. The algorithm is outlined in the flow skeleton (Figure 1).

**Figure 1.** Flow skeleton of the proposed method.
