Refined Exploitation of Time-Difference Analyses
By Bruce Rule - August 28, 2013
When multiple transient acoustic events (signals), the detection times of which can be measured with accuracies to the nearest second, are detected by three or more sea-floor sensors that are geographically dispersed, and for which the positions are known, the position of the acoustic events can be established to within one to two nautical mile in broad ocean areas. As discussed below, their relative positions can be determined with significantly greater accuracy.
In the case of the loss of the USS SCORPION (SSN-589) at 18:20:44Z on 22 May 1968, comparison of the detection times of the sixth signal in a series of more than 17 collapse event signals by Argentia arrays 3141, 3131 and two single hydrophones (A and D) located near the island of La Palma in the Canary Island archipelago established the position of the event within about one nautical mile (nm) of the wreck-site subsequently identified by a search based on the acoustically-derived position.
That time difference position-derivation analysis, per force, also established the relative time delays (differences) between arrivals of the same signal at the three sensors. Had any detections of the sixth acoustic event – or any other event detected by all three sensors - involved a reflection (echo) of the signal by a bathymetric feature (sea mount), no time-difference position could have been derived.
In the case of SCORPION, the time difference of arrival of the sixth signal involved a delay of three minutes and 11.5 seconds for array 3141 relative to the Canary Island hydrophone A . That delay resulted from the greater range to 3141 (976 nm) from the wreck-site compared to a range of 821 nm to Canary Island hydrophone A (derived speed of sound: 48.54 nm/min or an average of 4915 f/s)
If SCORPION continued to radiates acoustic signals from the same position, the delay relationship would not change, i.e., the 3141 event detections would always occur three minutes and 11.5 seconds after the Canary Island detections.
If; however, SCORPION changed position during the period when detections by both 3141 and Canary Island hydrophone A occurred, the value of three minutes and 11.5 seconds would also change. Since the Canary Island sensor was located to the east-southeast of the position where the SCORPION wreckage was located and array 3141 was located to the northwest, movement of SCORPION to the east during the period of mutual detection would increase the three minute and 11.5 second difference while any movement to the west would decrease that difference.
So, even though only some of the more than 17 SCORPION-associated collapse events were detected by both 3141 and the Canary island hydrophones, identification of the same time delays for those events confirms there was no significant horizontal (lateral) movement of the signal sources during the 111.6 second period when which it was conjectured in 1968 that SCORPION had reversed course.
Highly-refined Visicorder and Helicorder time of 3141 and Canary Island hydrophone A signal detection time measurements made on 18 July 1968 confirm the change in delays between the sensors over the 111.6 second period equated to horizontal movement of less than 100-feet by the sources of the collapse event signals.
Since it is known that the first acoustic event in the series was collapse of the SCORPION pressure hull at a depth of 1530-feet, the comparison of delays confirms the wreckage in which the subsequent collapse events occurred sank nearly vertically, I.e, there was no measurable horizontal movement by the collapse event signal sources during the 111.6 second period when the same four acoustic events were detected by the Canary Island and 3141 array sensors.
This conclusion is important because it refutes the basis for above mentioned conjecture that SCORPION had reversed course. Such a course-reversal was originally proposed in 1968 as a maneuver by SCORPION to disarm a Mk-37 torpedo that had started up within a torpedo tube.
Note again that, as discussed in the writer's letter of 10 April 2013 archived under ARTICLES on this website, 14 of the 17 (82 percent) of the conclusions by the SCORPION Court of Inquiry that were based on acoustic data were wrong;
This discussion provides an example of the use of time-delay measurements to provide refined assessments of signal source movements even at extreme detection ranges. This technique has obvious application in other circumstances.