Amplitude Distribution of Storm Microseisms 



US. NAVY MICROSEISMIC RESEARCH PROJECT 



31 



Figure 11. Hurricane tracked by micro-ratio technique in 1951 



the same point and smaller microseisms were 

 recorded at each station, but the ratio of their 

 microseisms was again 2.5. This fact has been 

 observed at all other points for which reliable 

 data are available. 



A chart utilizing such data can be made 

 by plotting on a map lines through all points of 

 equal ratio, Figure 9. Thus any storm gener- 

 ating microseisms that are recorded simultane- 

 ously at the two stations must be located along 

 the ratio line on a chart corresponding to the 

 ratio of the amplitude between the recorded 

 microseisms at the two stations. Similarly, a 

 ratio between either station and a third sta- 

 tion can also be computed and the intersection 

 of the two ratio lines will fix the position of the 

 storm, Figure 10. Naturally, when other sta- 

 tions record microseisms generated by the 

 same storm, the additional computed ratios will 

 greatly improve the accuracy of the fix. 



This method should locate and track a 

 storm in any area when three or more micro- 

 semic stations record vibrations solely from the 



storm, regardless of the storm's intensity, posi- 

 tion, its size or its -method of generating mi- 

 croseisms. The final accuracy of any micro- 

 ratio fix will depend principally upon the 

 amount and reliability of accumulated storm 

 data used in making the ratio charts between 

 each pair of stations and the number of stations 

 recording the storm simultaneously. An exam- 

 ple of the accuracy that has been obtained is 

 demonstrated in Figure 10 for hurricane ABLE 

 in August 1950. The five positions plotted along 

 the storm track were taken from the Fleet 

 Weather Central's final history of the storm. 

 The micro-ratio fixes corresponding to the ac- 

 tual storm positions are shown as the intersec- 

 tion of the three ratio lines. This was the first 

 attempt to use the micro-ratio charts and re- 

 sulted in positions not far from the true location 

 of the storm. 



The results of the second attempt is shown 

 in Figure 11. This shows the storm track, plot- 

 ted from advisories issued by the Fleet Weath- 

 er Central, and the track plotted from micro- 



