Changes to the airgun signal with increasing range.

Shown are representative recordings of the 40 in³ airgun with approx. 120 bar output pressure obtained at different ranges from the airgun. A: 6 m, B: 120 m, C: 200 m, D: 400 m, E: 800 m, and F: 1300 m. See legend to Fig 1 for explanation of subplots. Note that the y-axis on the center panel extends above 100 kHz for plot A and B compared to 10 kHz for the remaining plots, because of differences in sampling rates for the six stations. Note also the different y-axis scales in the time plots (top and bottom panels).