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Optical SETI Survey -Misconceptions (Part D)Radobs 7DVersion 1.0
1. While there has been little published material on Optical SETI in the
general literature, what there is, is generally grossly misleading and
incorrect? I am specifically referring to books on SETI which either
don't mention the optical approach, or dismiss it in a paragraph or
two. I am not referring to the few scientific papers that have been
written specifically on this subject. Do you agree that the general
references to Optical SETI are misleading? You may wish to review your
response to this question after completing the survey and reading my
earlier message about misleading SETI literature. Note that the
various bandwidths quoted are very approximate, for they substantially
depend on the assumed Effective Isotropic Radiated Powers (EIRPs) of
ETI transmitters.
YES
DON'T KNOW
NO
2. Do you think it plausible that successful detection of ETI signals
might require operation outside the atmosphere? This cosmic zoo or
non-interference directive restriction, might be purposely built into
ETI transmission techniques to avoid accidental detection and cultural
shock, until the targeted emerging technical civilization (ETC) has
literally begun to emerge from the confines of its planet.
YES
DON'T KNOW
NO
3. On the other hand, it is also reasonable to assume that successful
detection of ETI signals might not require receivers outside a
planetary atmosphere, either to overcome atmospheric absorption or
turbulence effects. Do you agree that this is also plausible?
YES
DON'T KNOW
NO
4. There are presently major developments occurring in ground-based
telescope technology in the form of new cheaper ways to manufacture
large, low-mass mirrors, and major advances in adaptive technology for
removing the "twinkle" from starlight. There is every indication that
within about five years, large ground-based adaptive optical telescopes
will be able to be used efficiently, i.e., at or close to the
diffraction limit, for conventional astronomy and Optical SETI. Do you
agree?
YES
DON'T KNOW
NO
5. The SETI lore that a visible wavelength ETI signal from a nearby star
system could not be detected because of Planckian radiation from its
star is incorrect, if it is assumed that the optical detection
bandwidth can be reduced below about 10 kHz. This question refers to
non-diffraction limited operation with the atmosphere. Do you agree
that the lore is incorrect?
YES
DON'T KNOW
NO
6. The SETI lore says that the only way a visible laser would be
electronically detectable, would be if its wavelength coincided with a
dark Fraunhofer line in the Planckian radiation from its star. This is
not true, though operation within the stellar absorption line can
increase SNR by up to about 20 dB if the star and transmitter are not
separately (spatially) resolved. Do you agree that the lore is
incorrect? This question is different to the previous one, and only
addresses the issue of whether the transmission frequency "must"
coincide with a Fraunhofer line for it to be detectable at any
reasonable optical bandwidth.
YES
DON'T KNOW
NO
7. The SETI lore that even a strong visible wavelength ETI signal from a
nearby star could not be detected in optical bandwidths greater than
about 1 MHz because of Planckian radiation from its star, is incorrect
if we assume the use of large diffraction limited space-based or
adaptive ground-based visible telescopes. These would allow spatial
(angular) separation of the transmitter and starlight, and would not
need the benefits of a 20 dB Fraunhofer suppression factor, though the
latter would help in increasing the SNR. Do you agree that the lore is
incorrect? This question differs from the previous two, in that it
addresses the benefits of having large receiving telescopes that are
diffraction limited.
YES
DON'T KNOW
NO
8. The other SETI lore that suggests that strong visible wavelength ETI
signals must be visible to the naked eye, and therefore it follows that
since we haven't spotted such signals they can't be there, is
incorrect. Its all a matter of using very small optical bandwidths for
detection, e.g. 10 kHz or less, and thus avoiding the requirement for
the transmitter to outshine its sun, whether or not the optical
receiver can spatially separate (resolve) the two sources. Do you
agree that the lore is grossly misleading?
YES
DON'T KNOW
NO
9. It is incorrect to say that since optical astronomers have been
collecting spectrographic plates for a century or more, and no
artificial spectral lines have been detected, it thus follows that
there are no extraterrestrial (extra-solar) visible laser transmitters.
Do you agree with this statement? This question is along the same
lines as the previous, but assumes far more sensitive detection (as
compared to the naked eye), through conventional, relatively broadband
incoherent detection techniques.
YES
DON'T KNOW
NO
Score out of 9: YES =
DON'T KNOW =
NO =
December 31, 1990
RADOBS.07D
BBOARD No. 297
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* Dr. Stuart A. Kingsley Copyright (c), 1990 *
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