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    Re: US. Navy fix accuracy and Interval.
    From: Brad Morris
    Date: 2013 Mar 28, 12:43 -0400

    Hi Lu

    Just suppose for a moment that you know your own acoustic signature.

    Just suppose that the ocean isn't silent but loaded with ambient noise from other sources.

    Suppose then that with appropriate signal processing that you could sense multipath arrivals, using the refraction of acoustical signals in the sea (Snell's law still applies!), to determine & map where "critical" bottom contours are.

    You wouldn't care about the bottom when it is beyond your operational range.  Of course, depth & speed are closely guarded secrets.  But lets pick an argument for talking.  Suppose 1 mile deep is max.  A coarse surface map, pinging away, would tell you were to look and not to look.  If the bottom is 2 miles deep, who cares about a pinnacle or sea mount that doesn't pierce the 1 mile window.

    Once a problem area is identified (like littoral regions in 'enemy' waters), passive listening, repetitively, to identify critical bottom features is feasible. 

    Is that how they do it?  Dang if I know Lu, they aren't ever really going to tell you.  That's one absolute truth!

    Brad

    On Mar 28, 2013 12:00 PM, "Lu Abel" <lu{at}abelhome.net> wrote:

    William:

    Without asking you to reveal anything classified, how can one survey the bottom without sonar?   And I thought subs didn't run active sonar because that would reveal their position.

    Lu


    On 3/26/2013 3:43 PM, William Hawes wrote:

    Lu,

    I'm sure you can appreciate that even after all these many years since I left the submarinne service, I can't give any details. Suffice it to say that submaines carry "classified" Bottom Contour Charts that allow navigation technniques not available to the general public. These special submarine chart folios were not even carried, at the time (mid 70's), on naval sufface ships.

    Guess what submarines are doing when they are not firing missiles - they are bottom surveying,

    wmh


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