Northrop 



Reflections from the Aleutian Islands (Reflector C of Fig. l) 

 last for 15 min. Travel time considerations indicate that the first 

 of this group of reflections is from the insular shelf south of 

 Kodiak^ Alaska. Continued reverberations were received from the 

 Aleutian Ridge as far west as the insular shelf south of Adak 

 Island. 



A series of short reflections from the Emperor Seamount Chain 

 (Reflector D of Fig. l) account for the next set of reverberations. 

 The first of this set of reflections is from a seamount on the 

 southern end of the seamount chain near 32°W, 179°E. The other 

 seamounts then cause a series of short (~10 sec) reflections on 

 the record. Echoes were recorded from the southern seamounts 

 before the northern ones. A reflection from the seamount near 

 490N, l69°E is the last to be received because the more northern 

 ones are in the shadow of the Aleutian Ridge. Identification of 

 individioal reflectors has been impossible because of the multiplic- 

 ity of seamounts and relatively poor bathymetric charts in the 

 area. 



After 8 min of low-level noise, a series of reflections was 

 received which lasted for 12 min. Individual bursts within this 

 time lasted from 10-^0 sec, with an average of 21 sec. The only 

 mapped submarine topographic feature that could account for these 

 reflections is the large (about 600 miles(96o km)long) shallow 

 rise known as Volshouki Ridge (Reflector E of Fig. l). This set 

 of reflections is therefore ascribed to individual peaks on the 

 Ridge . 



Reflections from the Kizril Islands next appear on the records 

 (Reflector F of Fig. l). The first echo is from Long Island 

 (U60N, 150°E), the more northern ones being in the shadow of the 

 Aleutians for great circle paths from Cape Mendocino. The Kuril 

 reflections all exhibit relatively low signal-to-noise ratio 

 (Fig. 6) because of: (l) the long ranges involved (~8000 miles 

 (1300 km)), (2) the interference of the intervening Emperor 

 Seamounts, and (3) the onset of propeller noise from an approach- 

 ing merchant vessel in the vicinity of FLIP. 



The last reflection identified on the FLIP records corres- 

 ponds to the submarine slope off the Island of Hokkaido, Japan 

 (Reflector G of Fig. l). This signal lasts for over half a 

 minute before it is finally lost in the increasing ship noise 

 which dominated the remainder of the record. 



Signal Level 



The signal level from a one kiloton charge at SOFAR 

 depth can be calculated from the equation: 



Ir=Io - (71+15 logio R) - 0.0035 R (1) 



32 



