Fig. 8

The blue curve in each of the four subplots represents guided waves collected from path 5-4 under different conditions: rain, freezing temperatures, direct sunlight, and through-hole damage, as indicated in the title of each subplot. The measurement time and temperature are labelled in the legend of each subplot. The background guided wave, marked with gray color, shown for comparison, was collected under fair weather conditions, as depicted in Fig. 3.