A scientist simultaneously records vlf signals under- 

 water and above the surface. The continuous 17.2-kc/s 

 unmodulated signals were received from Chollas 

 Heights Navy Transmitter approximately 13 miles 

 distant. A phase comparator produces dc signals 

 representing the relative phase of "air" and "under- 

 water" signals, which is charted as the "uncorrected 

 phase." The vlf underwater signal is electronically 

 modified, by compensating for the changing pressure 

 (depth) caused by sea-surface waves, to give a more 

 constant or corrected signal phase. 



UNDERWATER SIGNAL 

 PHASE-PERTURBATION 



B 



PRESSURE-SENSED 

 SUBMERSION DEPTH 



10 SEC 



Comparison of recorded (A) underwater observed 

 signal phase, (B) pressure at the receiver depth, and 

 (C) the more usable signal phase, corrected for 

 pressure (depth) at the receiver. 



67 



