auv-ee wrote:
As for the ambiguity in location, I doubt that it is due to navigational uncertainty, but rather due to acoustic localization uncertainty. I have no idea what signal processing was done to actually extract the signal from the noise, but it would likely have involved integration over long periods of time: as long as the sub, traveling at, say, 3-6knts to minimize self-noise, would have been within a few of km of the pinger. After a long integration, one would only be able to guess the location with a resolution of roughly that integration "distance" (time, times the sensor transit speed), i.e a few km.
Had I bothered to read the relevant sections of the two interim reports prior to posting, I could have avoided guessing the speed Emeraude transited while listening: 6-10 knots is listed in the second report.
Normally, a 20db signal-to-noise ratio is required for simple detection, resulting in the commonly quoted 2-3km detectable range.
Also, I see that the second report lists 2000-3200m as the assumed detection range for Emeraude, consistent with the above conclusion.
The report also cleared up something I was wondering about
: why were the TPLs from the US Navy not towed deep enough to hear? In fact they were towed deep, but they covered only the northern "ALPHA zone". If the Emeraude analysis is correct, they were simply towed in the wrong place.