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EJASA - Part 8
Page 50
Even as this is being written, substantial developments are being
made in terrestrial video compression techniques for High Definition
TeleVision (HDTV). Compression ratios as high as 100:1 have been
achieved with only a small reported impairment in perceived video
quality. [87] A 100:1 compression ratio would reduced bandwidth
required by the digitized video signal by a factor of 100. If it was
applied to an ETI interstellar communication system, the effective CNR
could be increased by 20 dB. Of course, we cannot yet comment on
whether ETIs would use such techniques, or what their level of
sophistication is. What we can say, however, is that optical communi-
cations technology, along with video compression techniques, would make
it much easier to transmit high-quality "real-time" video signals over
thousands of light years. What was previously thought possible with
old-fashioned analog TV signals and a 1 GW transmitter over ten light
years now becomes possible over one hundred light years.
ETI signals may be linearly or circularly polarization-modulated,
so that as previously mentioned, some means of analyzing the light would
be required to detect the modulation. This polarization analyzing
system could include a polarizer and a Soleil-Babinet compensator or
quarter/half-wave retardation plates. The latter might be spun to
cause sampling of all polarization states. If the signals are
frequency (or phase) modulated with relatively small deviations, then
only the professional heterodyne receiver will be able to recover the
modulation envelop, whatever the signal strength.
Shopping List -
1. 8"-14" (20-36 cm) or larger Schmidt-Cassegrain with periodic error
correction drive and RS-232 or IEEE-488 interface.
Low $2,000 High $12,000
2. CCD imaging and tracking system with RS-232 or IEEE-488 interface.
Low $1,100 High $3,200
3. Polarizaton analyzer.
Low $100 High $2,000
4. Fiber-optic umbilical and connectors (ten meters).
Low $150 High $150
5. Triple grating monochromator (resolution 0.1 to 0.01 nm) with
RS-232 or IEEE-488 interface.
Low $1,000 High $6,500
6. APD photon-counter or photomultiplier front-end.
Low $200 High $3,000
EJASA, Vol. 3, No. 6, January 1992
Page 51
7. Front-end cooling system.
Low $200 High $1,000
8. PC with fixed (hard) disk and RS-232/IEEE-488 interfaces.
Low $1,000 High $3,000
9. Spectrum analyzer PC card or stand-alone 0-10 MHz spectrum
analyzer.
Low $1,000 High $4,400
10. Video and audio monitors (PC may double-up for this purpose).
Low $200 High $200
11. Miscellaneous
Low $1,000 High $2,000
12. Labor - Free
Total cost: Low $8,000; High $38,000
Thus, the low-end cost is approximately $8,000; less if telescope
and computer system are already available. This is an affordable
activity for many clubs and societies. Some of the equipment above is
optional and may be replaced by less sophisticated devices, e.g., the
automatic scanning monochromator could be replaced by a manual
monochromator or a series of discrete high-Q bandpass filters, such as
a 656 nm H_alpha filter. By omitting the electrical spectrum analyzer
and using a fixed optical bandpass filter, instead of a scanning
monochromator, the cost of a rudimentary system adaptation to an
existing telescope would fall to about $3,000. This figure will be
affordable for some individual enthusiasts.
Instead of a scanning grating monochromator, a scanning grating
spectrometer might be used, where a linear CCD array is employed to
produce an essentially instantaneous display of optical spectra (over a
limited band) on a video display terminal (VDT). However, this does
not allow for the flexibility of employing a single photodetector
optimized for bandwidth and photon-counting sensitivity, and thus this
approach will be more expensive and/or less sensitive. Often, mono-
chromators use triple gratings in order to obtain spectral resolutions
of 0.01 nm or better. As previously mentioned, a set of four optical
fibers surrounding the signal fiber and corresponding low-bandwidth
photodetectors might be used in the system for fine guidance purposes.
Within this account of Amateur Optical SETI is the ambitious
desire to detect the modulation envelop. Hopefully, the ETI signals
will be intensity or polarization-modulated so that the modulation can
be detected by an incoherent receiver. For weak signals, we may only
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be able to detect the presence of an optical carrier or beacon (perhaps
Signpost SETI) and then only after some signal integration. However,
this would be a significant achievement by itself, allowing for more
powerful professional receivers to be built later for detecting the
modulation envelope.
As a spin-off from the MOP, electronic Multi-Channel Spectrum
Analyzers (MCSAs) could be developed for the Amateur Optical SETI
market, eventually making Amateur Optical SETI an even more affordable
activity for optical astronomy clubs and societies. Perhaps ETIs do
not expect their signals to be detected until the targeted civili-
zations make a collective, cooperative, and systematic search of their
home skies!
THE MICROWAVE AND OPTICAL OBSERVING PROJECT (MOOP)
The following is the author's tentative list of objectives for the
optical extension to MOP. It is called the Microwave and Optical
Observing Project, otherwise known by the acronym MOOP.
Project Goal: To continue the search for microwave (and millimeter
wave) signals of extraterrestrial intelligent origin
and to extend the search into the infrared and
visible spectrums.
Project Objectives:
1. To use existing large ground-based optical telescopes to carry
out a Targeted Search of about 800 nearby solar-type stars with
spectral resolution of 1 kHz and sensitivity 10^-16 W/m^2.
For selected laser wavelength bands corresponding to
atmospheric windows in the visible and infrared wavelength
range (350 nm to 12,000 nm).
2. To use existing large ground-based optical telescopes to carry
out a Targeted Search of about 1 million nearby solar-type
stars with spectral resolution of 100 kHz and sensitivity
10^-10 W/m^2. For selected laser wavelength bands corres-
ponding to atmospheric windows in the visible and infrared
wavelength range (350 nm to 12,000 nm).
3. To use dedicated groups of amateur astronomers and coordinate
their activities to conduct with their ground-based optical
telescopes a low-sensitivity Targeted Search of about 800
nearby solar-type stars with spectral resolution < 1 nm, and
sensitivity 10^-16 W/m^2. For selected wavelength bands in the
visible and near-infrared wavelength range (350 nm to 1,200 nm).
Duration: 2001 - 2010
Cost: $20M for starters. Assumes use of existing large ground-
based professional telescopes and the cost of modifying the
telescopes for adaptive reception and Optical SETI.
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==========================================================================
Table 5 Nearest stars favored for MOP's 800 star Targeted Search
==========================================================================
RGO RH DEC Relative Distance Apparent Spectral
Number H M S D M Vel. km/s L.Y. Magnitude Type
--------------------------------------------------------------------------
559A 14 36 11 -60 37.8 -22.2 4.39 -0.01 G2 eye, SB
559B 14 36 11 -60 37.8 -0.0 4.39 1.33 K0 eye
144 3 30 34 -9 37.6 +15.4 10.79 3.73 K2 eye
820A 21 4 40 38 30.0 -64.3 11.01 5.22 K5 eye, AB
820B 21 4 40 38 30.0 -63.5 11.01 6.03 K7 eye
845 21 59 33 -56 59.6 -40.4 11.20 4.69 K4 eye
71 1 41 45 -16 12.0 -16.2 11.77 3.50 G8 eye
380 10 8 19 49 42.5 -26.0 14.68 6.59 K7
166A 4 12 58 -7 43.8 -42.4 15.90 4.43 K1 eye
702A 18 2 56 2 30.6 -7.2 16.72 4.03 K0 eye, UD
702B 18 2 56 2 30.6 -10.0 16.72 6.00 K5 eye, SB
663A 17 12 16 -26 31.8 -0.7 17.25 4.32 K0 eye
663B 17 12 16 -26 31.9 -0.2 17.25 5.10 K1 eye
570A 14 54 32 -21 11.5 +19.5 18.11 5.78 K5 eye
664 17 13 9 -26 28.6 -1.3 18.31 6.34 K5
783A 20 7 55 -36 13.7 -130.3 18.42 5.31 K3 eye
764 19 32 28 69 34.6 +26.7 18.52 4.69 K0 eye
34A 0 46 3 57 33.1 +9.4 18.94 3.44 G0 eye
139 3 17 56 -43 15.6 +86.8 20.25 4.26 G5 eye
66A 1 37 54 -56 26.9 +22.5 21.32 5.07 K0 eye
66B 1 37 54 -56 26.9 +19.4 21.32 5.90 K0 eye
566A 14 49 5 19 18.4 +3.9 22.03 4.54 G8 eye
566B 14 49 5 19 18.4 +5.4 22.03 6.91 K5
892 23 10 52 56 53.5 -17.8 22.18 5.57 K3 eye
33 0 45 45 5 1.4 -12.6 22.62 5.75 K2 eye
105A 2 33 20 6 39.0 +23.4 22.64 5.82 K3 eye, UD
667A 17 15 33 -34 56.2 +1.2 23.29 5.91 K3 eye
667B 17 15 33 -34 56.2 -0.0 23.29 7.20 K5
17 0 17 29 -65 10.1 +8.8 23.44 4.23 G0 eye
68 1 39 47 20 1.6 -33.7 24.32 5.24 K1 eye
178 4 47 7 6 52.5 +24.3 24.70 3.19 F6 eye
673 17 23 16 2 10.2 -28.3 24.70 7.53 K7
666A 17 15 15 -46 35.1 +23.6 24.89 5.48 G8 eye
713 18 21 58 72 42.7 +32.5 25.27 3.58 F7 eye, SB AB
879 22 53 37 -31 49.8 +9.0 25.47 6.49 K5
117 2 50 7 -12 58.3 +18.8 25.67 6.05 K0
23A 11 15 31 31 48.6 -15.5 25.67 3.79 G0 eye, SB AB
423B 11 15 31 31 48.6 -15.9 25.67 4.80 G0 eye, SB
216B 5 42 21 -22 26.2 -10.1 26.50 6.15 K2
216A 5 42 23 -22 27.8 -9.7 26.50 3.60 F6 eye
502 13 9 32 28 7.9 +6.1 27.17 4.26 G0 eye
785 20 12 10 -27 11.0 -54.2 27.17 5.73 K0 eye, SB
506 13 15 47 -18 2.0 -8.5 27.39 4.74 G6 eye
827 21 22 20 -65 35.6 -29.5 28.10 4.22 F6 eye
231 6 11 44 -74 44.2 +34.9 28.35 5.08 G5 eye
75 1 44 6 63 36.4 +1.8 28.59 5.63 K0 eye
==========================================================================
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Table 5 is an extract from the list (provided by the SETI
Institute) of the closest stars that form the group of 800 stars which
are subject to MOP's "Targeted Search". [40-45] Presently, the list
covers stars in the range of 4.39 to 81.5 light years from Earth, but
is subject to review.
UD = White Dwarf 559A = Alpha Centauri A
EB = Eclipsing Binary 144 = Epsilon Eridani
AB = Astrometric Binary 71 = Tau Ceti
SB = Spectral Binary
eye = Visible to the unaided eye under good conditions (apparent
visual magnitude less than 6.0 - about 224 stars).
The Amateur Optical SETI system just described is quite capable of
being upgraded in sensitivity by slaving "n" similar telescopes
together, and combining the photons from the "n" optical fibers through
a single monochromator and photon-counter. In this way, ten telescopes
of 25-cm (10") aperture would have approximately the same sensitivity
as a single 81-cm (32") telescope, but in a more cost-effective manner.
Of course, ten small telescopes would not have the same ability as a
32" (81 cm) telescope to reject the effects of daylight, should
daylight Optical SETI be desired. The approach could be adopted, as
with the original Cyclops Study, to gradually increase the number of
telescopes as the need arises and availability of funding, assuming
that ETI signals are not detected soon after system activation.
A large, single barrel, telescope could be constructed using
several smaller mirrors, each with its own focus and optical fiber. In
this way, only one drive system would be required. A much simpler
construction is possible because we do not need to image a star field,
just collect as many photons as possible from the region around a
single star (light-bucket mode of operation). This could be somewhat
like the Multi-Telescope Telescope (MTT) that has been designed by
Georgia State University's (GSU) Center for High Angular Resolution
Astronomy (CHARA). [92]
LIST OF PREVIOUS AND PRESENT OPTICAL SETI ACTIVITIES
The following material has been extracted from a comprehensive list
on all modern-day SETI activities so far, and was prepared in October
of 1991 by Dr. Jill Tarter of the SETI Institute.
Dr. Tarter lists sixty three different SETI observing programs,
starting with Project Ozma in 1960 at the Green Bank National Radio
Observatory in West Virginia, to Harvard University's microwave search
of Messier M31 and M33 from the Oak Ridge Observatory. This list also
includes the 1983-1984 Amateur Microwave SETI program organized by
Dr. Kent Cullers, which used Silicon Valley Hams with their satellite
TV dishes (TVROs).
Of this list of sixty three observing programs, only three were or
are concerned with Optical SETI, and these optical programs are listed
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below. Optical SETI observing programs currently amount to less than
5 percent of all SETI programs to date. In actuality, the ratio is
nearer 3 percent because Shvartsman's two programs can be considered as
one. This supports the author's contention that Optical SETI has
suffered benign neglect.
Date: 1973 - 1974
Observer(s): Shvartsman et al. "MANIA"
Site: Special Astrophysical Observatory
(former Soviet Union)
Instrument Size (m): 0.6
Search Wavelength (nm): 550
Frequency Resolution (Hz): df = 100 kHz (dWl = 10^-7 nm)
Objects: 21 Peculiar Objects
Reference: 48
Comments: Optical search for short pulses of length
3 X 10^-7 to 300 seconds, and narrow
laser lines. Prototype for later system
on 6 m telescope.
Date: 1978 to Present
Observer(s): Shvartsman et al. "MANIA"
Site: Special Astrophysical Observatory
(former Soviet Union)
Instrument Size (m): 6
Search Wavelength (nm): 550
Frequency Resolution (Hz): df = 100 kHz (dWl = 10^-7 nm)
Objects: 93 Objects
Flux Limits: < 3 X 10^-4 of the optical flux is
variable in any object observed.
Total Hours: 250
Reference: 54 and 58
Comments: Have searched 30 Radio Objects with
Continuous Optical Spectra to date,
looking for optical pulses from
potential Kardashev type II or III
civilizations.
Date: 1990 to Present
Observer(s): Betz
Site: Mt. Wilson
Instrument Size (m): 1.65 m element of Townes IR
Interferometer
Search Wavelength (um): 10.6
Frequency Resolution (Hz): 3.5 MHz (35 m/s)
Objects: 100 nearby solar-type stars
Flux Limits: 1 MW transmitter out to 20 psc
Total Hours: Continuing
Reference: 57
Comments: Search for IR beacons at CO2 laser
frequency using narrowband acousto-
optical spectrometer.
Continued
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