Rob,
[snip,snip]
Ah! So you read the FAQ. Humm :-) That's great!
I'll check into this too ...
(I wish I knew more about military radars myself ... space surviellance
radars for example)
You're right though, sounds like a special radar is needed.
Arecibo, of course, is a very special radar and very powerful one too
used
in part for pinging off Solar System objects (planets, asteroids...)
(100 KW omni power isn't much though generally speaking nowadays)
(Arecibo, I think, transmits at 1-10 Megawatts ...it "can" put 10's of
terrawatts of power in a narrowband beam)
I wouln't count Arecibo though, because the odds of detection, even with
great SNR, would be very slim (one might need to look our way for ages
before one saw a ping ...)
I distinctly remember that some of the military radars could be detected
100
LY's away ... but I'll recheck all this ...
I'll get back here soon ...
Al
Yeah. We need to know more about radar, and the signals they produce
(frequency/power/modulation/rotation speed etc). I dont know enough about
that.
I'm sure there are some radar systems which indeed transmit in this 40GW
EIRP range.
Arecibo will easily be able to do that, but only points at a fixed point
in the sky
twice a year or so. Not much repetition for any ET that is listening.
So the question is how many of these high-power radar systems are actually
operating
say, on a dayly basis, and how often their beam points to an fixed point
in the sky.
That would say something about the probability that a high-power
transmitter
actually points at us (again assuming an earth-like civilisation 5 LYs
away).
The other thing that is interesting is the 'application' for these
high-power radar's.
If ET is smart, they will find an optimal frequency band, and optimal
modulation
technique/bandwidth/pulse, and optimal sky-coverage repetition rate
depending on
the application they have in mind. An astroid radar for example would not
need to
cover the sky more often than once/day, but needs deep space (sensitive)
detection
requirements. Also the reflected signal will take minutes to hours to
return, which
also impacts the design of the system.
We need a radar expert to give us some better idea of trade-offs of
what kind of signal we could expect to hear from what kind of application.
We know from previous SETI's (project Phoenix etc) that there are no
obvious,
super-loud microwave signals out there.
Wait a minute! We were just talking about how difficult it is to detect even
with a powerful radar or whatever!
I claim you can't make that claim (this statement is far from proven: "there
are no obvious, super-loud microwave signals out there.") ... First of all
Project Phoenix has only looked at several hundreds of stars ... they didn't
do an all sky search ... they only looked for a few hours at each star ...
what is the probability they missed something? I'd bet instead that their
certainty of "no one there" for those stars they have searched (to say
nothing of those billions and billions of other stars in the Galaxy) is low
to very low. Same for seti@home. Same for project META and Project BETA. I
hope that these scientists someday get down to the nitty gritty and figure
out what the real odds of detection are ....
Heck, I'll be dead in 20 years! :-) ... can't wait too much longer! :-) ...
all I can do is beat the bushes hoping that someone wakes up soon :-)
You're sort of right though. There doesn't appear to be really big
techological civilizations out there --- nothing really obvious ... it does
seem quiet out there. What I'd like to know though, clearly, is that due to
the fact that the probability of detection is so very very poor or is it due
to the fact that there _really_ isn't anyone out there. How can one model
this so that one can begin to understand? If I was at Mars for example and
looked back at Earth and did a spectrum analysis for say days (a week or two
perhaps) what would I see from Earth in terms of electromagnetic energy?
What do we look like? What's Earth's EM signature like? Once we know this,
then how far away could we detect Earth given some fixed resources (antenna
size, etc. ...)?
And beacons are also hard to find.
Yes ..
At least around 1.42 GHz. But we do not produce super-loud microwave
signals,
Arecibo does ...
Maybe others too ...
and we also don't have a beacon round 1.42 GHz. So why would ET have that
?
There have been a few Russian transmissions of signals to specific stars (or
areas in space say) ...
Maybe it is time to focus on applications that ET really could use, and
then
figure out how the signals of these applications would sound like here,
and where
we could find them in the spectrum.
If in the end it turns out that we would need to build a $100B device to
detect
(with some certainty) a civilisation of our own level within a 1000LY
range from earth,
but it would only take $10B to build a device which can detect (with some
certainty)
oxygen on planets in a 1000LY range, then I'd put my money in the oxygen
detector first...
)
Sounds reasonable doesn't it. SETI is on the fringe ...
Now we've come full-circle on the science and funding aspects of SETI.