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From: pbrewer@urbana.mcd.mot.com (Philip Brewer)
Newsgroups: sci.bio
Subject: Re: BATS revisited
Message-ID: <1991Jun26.135544.16307@urbana.mcd.mot.com>
Date: 26 Jun 91 13:55:44 GMT
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> Two points of interest here.  First of all, for what it is worth, the 
> echo-location calls of bats are pulses of short duration and vary in 
> frequency and rep-rate as a function of distance to the target.

Different species of bat echo-locate different ways.  One well-studied
species (I forget which one, but could find out if anybody is really
interested) varies pulse frequency and rep-rate in a more complex
fashion than just as a function of distance to the target.

First, they use one sort of call to locate a possible prey object.  Once
they have one, they switch to a different call.  This latter call is
tuned so that the echo return will doppler back at a specific frequency.
If the echo return is not at that frequency, it means that the bat's
notion of the relative velocity was wrong.  It will then change the tone
of the call based on a new estimate of relative velocity.  So, they
extract more data from the pulse return than simply the range. 

They can estimate the range based on not only the time between call and
pulse, but also (since they know the closing rate) based on the previous
range minus the relative distance traveled.

-- 
Philip Brewer                   pbrewer@urbana.mcd.mot.com
Motorola Urbana Design Center   ...!uiucuxc!udc!pbrewer
Kie estas la fajro, mak?