Re: Judge bans Navy from using sonar off Southern California
- From: "Brian Sharrock" <b.sharrock@xxxxxxxxxxxx>
- Date: Wed, 08 Aug 2007 14:59:40 GMT
"Richard Casady" <richardcasady@xxxxxxxxxxxxx> wrote in message
news:46cfb821.597251500@xxxxxxxxxxxxxxxxxxxxxxxxxx
On Tue, 07 Aug 2007 02:27:08 -0700, Jack Linthicum
<jacklinthicum@xxxxxxxxxxxxx> wrote:
A federal judge in Los Angeles banned the U.S. Navy from using high-
powered sonar in nearly a dozen upcoming training exercises off
Southern California, ruling Monday that it could "cause irreparable
harm to the environment."
I don't suppose one could dial up the power gradually, so that the
whales would have an opportunity to clear the area. Too obvious?
Casady
AIUI; the 'high powered sonar' referred to is _Active_ sonar.
An _active _sonar 'works' by emitting a sound source (basically a 'ping' ,
although swept and chirping sources are possible) and 'listening' for the
return. Range and Bearing of a returning echo can be determined and with
more processing, the 'up' Doppler and 'down' Doppler frequency of the
returning echo enable more information about the echoing surface can be
derived.
in other words, to obtain _range_ requires _time_. It's a rough rule of
thumb that a target can hear (detect) the 'ping' long before the transmitter
can 'hear' the echo. Start to 'gradually' increase the magnitude of the
'ping' and the bad guys will have cleared the area long before the
transmitting guys have detected its presence.
AIUI, a active 'ping' is pretty much a single event , used almost in
desperation ; because the 'ping' tells the target more about the transmitter
than the transmitter can learn from the echo of its ping.
--
Brian
.
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