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Optical SETI Survey -Misconceptions (Part D)

Radobs 7D

Version 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.
                                                                     DON'T KNOW

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.
                                                                     DON'T KNOW

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?
                                                                     DON'T KNOW

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
                                                                     DON'T KNOW

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?
                                                                     DON'T KNOW

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.
                                                                     DON'T KNOW

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.
                                                                     DON'T KNOW

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?
                                                                     DON'T KNOW

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.
                                                                     DON'T KNOW

Score out of 9: YES        =
                DON'T KNOW =
                NO         =

December 31, 1990
BBOARD No. 297

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* Dr. Stuart A. Kingsley                       Copyright (c), 1990        *
* AMIEE, SMIEEE                                                           *
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