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From: cpshah99 on 8 Jul 2008 10:52
Hello People

In underwater communications, assume there is one direct path and one
surface reflected path. And the receiver is moving at 0.1 m/s (either
towards or away from transmitter).

My question is: do both the paths have same doppler effect?

Your guidance will be greatly appreciated.

Regards,

Chintan
From: Fred Marshall on 8 Jul 2008 13:13

"cpshah99" <cpshah99(a)rediffmail.com> wrote in message
news:ip-dnSHHVZ2J4u7VnZ2dnUVZ_rPinZ2d(a)giganews.com...
> Hello People
>
> In underwater communications, assume there is one direct path and one
> surface reflected path. And the receiver is moving at 0.1 m/s (either
> towards or away from transmitter).
>
> My question is: do both the paths have same doppler effect?
>
> Your guidance will be greatly appreciated.
>
> Regards,
>
> Chintan

The surface acts like a mirror so the reflection looks like it's coming from
a source that's above the surface. Motion would be the same but the
geometry is not - whether it's negligible or not is something you can
decide.

If the source and the receiver are at the same depth then the radial
velocity (which is what's important for Doppler) is the same as the
horizontal velocity - which I assume is what you mean as "moving toward or
moving away".

The reflected source would have the same horizontal velocity but not the
same radial velocity. Can you see why?

Fred


From: Jerry Avins on 8 Jul 2008 13:31
Fred Marshall wrote:

...

> The reflected source would have the same horizontal velocity but not the
> same radial velocity. Can you see why?
Sure. Geometry. :-)

Jerry
--
Engineering is the art of making what you want from things you can get.
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From: cpshah99 on 8 Jul 2008 16:21
>
>"cpshah99" <cpshah99(a)rediffmail.com> wrote in message
>news:ip-dnSHHVZ2J4u7VnZ2dnUVZ_rPinZ2d(a)giganews.com...
>> Hello People
>>
>> In underwater communications, assume there is one direct path and one
>> surface reflected path. And the receiver is moving at 0.1 m/s (either
>> towards or away from transmitter).
>>
>> My question is: do both the paths have same doppler effect?
>>
>> Your guidance will be greatly appreciated.
>>
>> Regards,
>>
>> Chintan
>
>The surface acts like a mirror so the reflection looks like it's coming
from
>a source that's above the surface. Motion would be the same but the
>geometry is not - whether it's negligible or not is something you can
>decide.
>
>If the source and the receiver are at the same depth then the radial
>velocity (which is what's important for Doppler) is the same as the
>horizontal velocity - which I assume is what you mean as "moving toward
or
>moving away".
>
>The reflected source would have the same horizontal velocity but not the

>same radial velocity. Can you see why?
>
>Fred
>
>
>
%%%

HI Fred

Thanks very much for replying.

I am sorry but I am not getting your point. Just assume that there is no
surface reflection. Also the TX and RX are at same depth. TX is steady and
RX is moving. So the signal will be expnaded by the velocity. Is this
correct?

And as you are saying, 'The reflected source would have the same
horizontal velocity but not the same radial velocity.' I am not getting
this point.

I have found all the angles and lenths of signal but I have no idea how to
use them.

Thanks again.

Chintan
From: John Monro on 8 Jul 2008 21:51
cpshah99 wrote:
> Hello People
>
> In underwater communications, assume there is one direct path and one
> surface reflected path. And the receiver is moving at 0.1 m/s (either
> towards or away from transmitter).
>
> My question is: do both the paths have same doppler effect?
>
> Your guidance will be greatly appreciated.
>
> Regards,
>
> Chintan

No they don't, because the reflected path-length is changing at a
different rate from the direct path-length.

Regards,
John
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