| Optical SETI Map | Conferences Map | Illustrations Map | Photo Galleries Map | Observations Map | Constructing Map |
|
Optical SETI Survey -Facts (Part E)Radobs 7EVersion 1.0
1. Once adaptive telescope technology is perfected, say within five years,
night time Optical SETI observations will be able to be done at visible
wavelengths with large ground-based adaptive telescopes, even with a
dark sky suffering substantially from light pollution effects. Do you
agree?
YES
DON'T KNOW
NO
2. Furthermore, daytime Optical SETI will then also be able to be done at
visible wavelengths with large ground-based adaptive telescopes under a
clear blue sky! Optical SETI at the far-infrared CO2 wavelength of
10,600 nm is more problematic, even though there is an atmospheric
window, because of the approximate 300 K sky temperature, day or night.
This severely limits the optical detection bandwidth that can be
employed without degradation in signal-to-noise ratio. Do you think
that visible SETI can be done in daylight?
YES
DON'T KNOW
NO
3. The more than 100,000 times increase in Doppler shifts (fixed frequency
offsets) at visible wavelengths with respect to that at microwaves, is
not a problem since this only represents a very small uncertainty on
top of a much larger uncertainty in not knowing the "magic
frequencies". Thus, assuming the availability of local-oscillator
receiver lasers that can be tuned across the entire visible spectrum,
the extra frequency uncertainty doesn't really make it any the more
difficult to acquire a signal for the first time. However, the effort
to acquire the signal again would be increased if its frequency had
changed in between observations. Would you agree with this sentiment,
which seeks to indicate that the actual Doppler shifts are not that
important? What is more important is the Doppler drifts or chirps
which are discussed in the following question.
YES
DON'T KNOW
NO
4. The more than 100,000 times increase in Doppler chirps (drifts) at
visible wavelengths with respect to that at microwaves, is not a
problem, because we would expect the aliens to de-chirp their signals
at the transmitter, and we could de-chirp the receiver to take out our
local chirp. Thus, most of the induced chirp could be compensated for
with relatively simple electronics. Once a signal was acquired
(found), conventional automatic frequency control techniques would
allow our receivers to track the received frequency. Do you think that
advanced technical civilizations (ATCs), aware that the problem of
spectral spreading caused by rapidly drifting frequencies would reduce
the detectability of their signal, would de-chip their transmissions?
YES
DON'T KNOW
NO
5. Single mode laser linewidths can be obtained which are less than 1 kHz.
Do you agree?
YES
DON'T KNOW
NO
6. Interstellar dispersion effects (spectral spreading) at visible and
infrared wavelengths over distances less than 10,000 light years is
negligible. Do you agree?
YES
DON'T KNOW
NO
7. Interstellar absorption in the galactic plane at visible wavelengths is
negligible up to a thousand light years. Do you agree?
YES
DON'T KNOW
NO
8. Interstellar absorption outside the galactic plane (> +/- 20 deg.) at
visible wavelengths is negligible over thousands of light years. Do
you agree?
YES
DON'T KNOW
NO
9. Interstellar absorption in the galactic plane at infrared wavelengths
is generally negligible across the entire galaxy. Do you agree?
YES
DON'T KNOW
NO
10. Laser powers available to ATCs are likely to be huge, and at least as
powerful as the microwave power available. Do you agree?
YES
DON'T KNOW
NO
11. Just because huge microwave systems have the ability to transmit across
the entire galaxy, and beyond, does not imply that they would also be
used for relatively short ranged interstellar communications. Do you
agree with this statement?
YES
DON'T KNOW
NO
12. ATCs are likely to put their transmitters in orbit about their stars,
and have them nuclear-pumped or directly pumped by radiation from their
stars. A separate stellar orbit would minimize Doppler chirp and
reduce any danger caused by the high power beam densities in the near-
field. Do you agree that this is plausible.
YES
DON'T KNOW
NO
13. Because the efficiency of optical transmitters in getting signal energy
to a particular target is much higher than with large microwave
systems, we can expect the signal bandwidths and signal-to-noise ratios
to be much higher than is presently predicted for the microwave
spectrum, even considering the various noise penalties. Indeed, the
requirement for high bandwidths may well be the overriding
consideration for preferring optics to microwaves. In the optical
regime, larger bandwidths are also more compatible with the effects
mentioned above, such as Doppler chirp and finite laser linewidths. Do
you agree that information bandwidths are likely to be significantly
greater?
YES
DON'T KNOW
NO
14. For the same signal strength and information rate reasons, the number
of frequencies to search in the optical spectrum is not likely to be
100,000 times or more greater than the number of frequencies in the
microwave spectrum. Each channel will have a bandwidth much greater
than 1 Hz or a few tens of Hz, and hence the optical spectrum need not
be subdivided into 1 Hz bins as part of the search strategy.
Obviously, this considerably eases the magnitude of the "search"
problem. Perhaps each bin should be 10 kHz to 1 MHz wide, or even
greater. Does this wider bin width assumption seem plausible for the
search strategy? The aim of this question is to show that while the
"optical search" is much more difficult than the microwave search, in
terms of time and effort, it is by no means 100,000 times the time and
effort. It may only require about ten times the effort, even less if
we concentrate only on those regions of the optical spectrum that are
at and adjacent to, future identified "magic frequencies".
YES
DON'T KNOW
NO
Score out of 14: YES =
DON'T KNOW =
NO =
December 31, 1990
RADOBS.07E
BBOARD No. 298
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* Dr. Stuart A. Kingsley Copyright (c), 1990 *
* AMIEE, SMIEEE *
* Consultant "Where No Photon Has Gone Before" *
* __________ *
* FIBERDYNE OPTOELECTRONICS / \ *
* 545 Northview Drive --- hf >> kT --- *
* Columbus, Ohio 43209 \__________/ *
* United States .. .. .. .. .. *
* Tel. (614) 258-7402 . . . . . . . . . . . *
* skingsle@magnus.ircc.ohio-state.edu .. .. .. .. .. *
* CompuServe: 72376,3545 *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
| ||||||