Re: Mass and Point



Steve Bell wrote:
"doug" <xx@xxxxxx> wrote in message news:wOednUapOJG2BcrXnZ2dnUVZ_qGdnZ2d@xxxxxxxxxxxxxxxxx

If you think what I said, which are the *classic* assumptions, is "going off the deep end," you obviously don't understand the statistical assumptions behind radar transmitter/receiver theory. I will condescending suggest you study more and suggest the well know text "Spotlight-Mode Synthetic Aperture Radar: A Signal Processing Approach" by C. Jakowatz et. al.

I think you need to go back to the book. Radar reflection is
deterministic. I get the same return from the same target
every time. The signal processing is a different issue.


I think you don't understand what's physically going on. It has nothing to do with signal processing, per se. If these physically
ridiculous complex reflectivity's actually *are out there,*


It is pretty clear you do not understand what phase is. The students in
circuit theory classes I taught understood that, those in the E&M
classes certainly did not get out without understanding that.

Take a network analyzer and look at the return from a short circuit
and then look at the return from an open circuit. They have the
same amplitude but a different phase. That is, they have a complex
reflectivity. It does not get any simpler than this. The scattering
from a target is the same thing. You can even do radar returns
with the network analyzer and see the changes yourself.


like what is insanely assumed by the maniac radar *and* QM physicists,
then each point scatterer gets the phase of its reflection changed from what it's suppose to be to something completely uniform random between 0 and 2*pi.

No, this is completely wrong. The phase is deterministic. There is no
random issue involved at all. Perhaps you are misunderstanding the
random fluctuations from from the path issues in the atmosphere
with that of the targets.

This happens at the physical instant of the reflection. Then all these completely scrambled point
reflections superposition at the surface of the array (are you following the *physics*?) and will *always* create a white superposition with absolutely no "correctly deterministic" phases. The superposition at the surface of the array under these incorrect assumptions *always* ends up being the actualization of a white noise process. It is these obnoxious white random phase shifts imposed at the instant of reflection that destroys the deterministic information in the signal, which is directly quantified as autocorrelations (when it comes to complex-valued correlations, phases are unbelievably important). But what is the autocorrelation structure of a white noise process? No autocorrelations, that's what, and presto-zappo, the Fourier transforms (spectra) always come out flat and the 2-D real image is grey-speckled. I've verified this many times using Monte Carlo computer simulations.

Sure, if you transform a random number, you do not get much
of interest.


You are ignoring that there are different types of radar. A strict
pulsed radar with no phase information has to work only with amplitude.
But that is not the only kind of radar and that does not mean the
information is not there.



I was and have always been referring to modern sophisticated receiver circuitry that performs a downconversion to baseband with the I and Q signals then digitized and downloaded to the ground. The I and Q signals are then polar-to-rectangular reformatted, a 2-D Fourier transform performed (range and azimuth compression), then the moduli of the result is taken to form a 2-D real image. There are other minor processing steps along the way, but these are the basics.

Then you should not have misunderstood the reflectivity issues.



It seems to me you do not understand the basics of radar receiver theory. Really, if you thought what I said above is "off the deep end," which are the classic assumptions about "clutter models," you really don't know what you are talking about.

You are mistaking clutter for reflections. The process of reconstruction
of signals in clutter uses statistical models for the removal but the
actual reflectors themselves have no idea whether we consider them
clutter or signal.



Are you talking MTI or SAR? It sounds like MTI to me. In SAR imaging *every* point target is *signal*, bright or dim, because we want an image of everything on the ground.

You were the one referring to clutter. As I said, the reflectors
do not know whether we are interested in them. But we do work
on both.



Yes, I imagine you will continue to believe in magic, which is *exactly* what you are doing when assuming complex-valued physical variables exist in a real-valued world.

Of course they do. Your unwillingness to think is sad. Everytime
you notice where a sound comes from, you are using complex
values since your brain determines the source of sound using
the phase difference. That is only the start.


Like all people who think the external world is complex-valued, you are lost in an imaginary world.

Since you do not believe in basic math or electronics, you never
would have made it through any of my classes. How can you claim
to be an engineer and not know about phase?

Steve Bell


.

Relevant Pages

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  • Re: Mass and Point
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  • Re: Mass and Point
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