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Detectability of Extraterrestrial Technological Activities

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Author Topic: Detectability of Extraterrestrial Technological Activities  (Read 340 times)
Jennifer Murdoch
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« Reply #15 on: February 04, 2010, 01:21:12 pm »

       Where PHImin is  the  sensitivity  of  the search system in [W m-2].
       For the NASA HRMS Target Search PHImin  =  10exp  (-27)  and for the
       NASA HRMS Sky Survey PHImin w 10exp(-23) (f)exp(1/2), where f is the
       frequency in GHz.  Table 3 shows the distances where the Arecibo and
       BMEWS transmissions could  be  detected  by  a  similar   NASA  HRMS
       spectrometer.

         TABLE 3: HRMS Sensitivity for Earth's Most Powerful Transmissions:

       ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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Jennifer Murdoch
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« Reply #16 on: February 04, 2010, 01:21:26 pm »

     ARECIBO PLANETARY RADAR

        (1) TARGETED SEARCH                   MAXIMUM RANGE (light years)

              Unswitched
                 With CW detector               4217
                 With pulse detector            2371
              Switched
                 With CW detector               94
                 With pulse detector            290

        (2) SKY SURVEY

              Unswitched
                 CW detector                    77
              Switched
                 CW detector                    9


                                              BMEWS

        (1) TARGETED SEARCH
              Pulse transmit CW detector        6
              Pulse transmit pulse detector    19

        (2) SKY SURVEY
              Pulse transmit CW detector        0.7

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Jennifer Murdoch
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« Reply #17 on: February 04, 2010, 01:21:40 pm »

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

       All these calculations assumed that the transmitting civilization is
       at the same level of technological evolution as ours on Earth.

       Von Hoerner (1961) classified the possible nature of the ETC signals
       into three general  possibilities:  Local communication on the other
       planet, interstellar communication  with  certain distinct partners,
       and a desire  to attract the attention of unknown  future  partners.
       Thus he named  them  as  local  broadcast,  long-distance calls, and
       contacting signals (beacons).  In  most of the past fifty SETI radio
       projects, the strategy  was  with  the  hypothesis  that  there  are
       several civilizations transmitting omnidirectional beacon signals.

       Unfortunately, no one has been able to show any positive evidence
       of this kind of beacon signal.

       Another possibility is   the   radio   detection   of   interstellar
       communications between an ETC planet  and  possible  space vehicles.
       Vallee and Simard-Normandin (1985) carried out a search for these

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Jennifer Murdoch
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« Reply #18 on: February 04, 2010, 01:21:57 pm »

       kind of signals  near  the  galactic  center.   Because  one  of the
       characteristics of artificial transmitters (television, radar, etc.)
       is the highly  polarized  signal   (Sullivan  et  al,  1978),  these
       researchers made seven observing runs of roughly three  days each in
       a program to  scan  for  strongly  polarized  radio  signals  at the
       wavelength of lambda=2.82 cm.

       Radar Warning Signals

       Assuming that there is a certain  number  N  of civilizations in the
       galaxy at or  beyond  our  own  level  of  technical  facility,  and
       considering that each  civilization is on or near a planet of a Main
       Sequence star where  the planetoid  and  comet  impact  hazards  are
       considered as serious   as   here,  Lemarchand  and   Sagan   (1993)
       considered the possibility  for detecting some of these "intelligent
       activities" developed to  warn  of   these   potentially   dangerous
       impacts.

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Jennifer Murdoch
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« Reply #19 on: February 04, 2010, 01:22:14 pm »

Because line-of-sight radar astrometric measurements have much finer
       intrinsic fractional precision  than  their  optical  plane-of-sight
       counterparts, they are   potentially   valuable   for  refining  the
       knowledge of planetoid and comet  orbits.   Radar  is  an  essential
       astrometric tool, yielding both a direct range to  a  nearby  object
       and the radial  velocity  (with  respect  to  the observer) from the
       Doppler shifted echo (Yeomans et  al,  1987,  Ostro et al, 1991, and
       Yeomans et al, 1992).

       Since in our  solar  system, most of Earth's nearby  planetoids  are
       discovered as a  result  of their rapid motion across the sky, radar
       observations are therefore   often    immediately    possible    and
       appropriate.

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Jennifer Murdoch
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« Reply #20 on: February 04, 2010, 01:22:24 pm »

A single radar   detection  yields  astronomy  with   a   fractional
       precision that is  several hundred times better than that of optical
       astrometry.

       The inclusion of radar with the optical  data  in the orbit solution
       can quickly and  dramatically  reduce future ephemeris  uncertainty.
       It provides both impact parameter and impact ellipse estimates.

       This kind of radar research gives a clearer picture of the object to
       be intercepted and  the  orientation  of  asymmetric bodies prior to
       interception.  This is  particularly   important  for  eccentric  or
       multiple objects.

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Jennifer Murdoch
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« Reply #21 on: February 04, 2010, 01:22:37 pm »

 Radar is also the unique tool capable for making  a  survey  of such
       small objects at  all  angles  with respect to the central star.  It
       can also measure reflectivity and polarization to obtain physical
       characteristics and composition.

       For this case,  we  can assume that  each  of  the  extraterrestrial
       civilizations in the  galaxy  maintains  as good a  radar  planetoid
       and/or comet detection and analysis facility as is needed, either on
       the surface of  their  planet, in orbit, or on one of their possible
       moons.

       The threshold for the Equivalent Isotropic  Radiated Power (EIRP) of
       the radar signal  could  be  roughly estimated by the  size  of  the
       object (D) that they want to detect (according to the impact hazard)

                                      Page 8
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Jennifer Murdoch
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« Reply #22 on: February 04, 2010, 01:22:50 pm »

       and the distance  to  the  inhabited  planet  (R),  in order to have
       enough time to avoid the collision.

       One of the  most  important  issues   for   the   success   of  SETI
       observations on Earth is the ability of an observer to detect an ETC
       signal.  This factor is proportional to the received  spectral  flux
       density of the radiation.  That is, the power per unit area per unit
       frequency interval.  The  flux  density  will be proportional to the
       EIRP divided by the spectral bandwidth  of  the  transmitting  radar
       signals B.

       The EIRP is  defined  as  the product of the transmitted  power  and
       directive antenna gain  in  the  direction of the receiver as EIRP =
       PT.G, where PT is the transmitting  power  and  G  the antenna gain.
       This quantity has units of [W/Hz].

       According to the kind of object that the ETC wants to detect (nearby
       planetoids, comets, spacecraft, etc.), the distance  from  the radar
       system and the  selected  wavelength,  a  galactic civilization that
       wants to finish a full-sky survey  in only one year, will arise from
       a modest "Type 0" (w10exp13 W/Hz, Rw0.4 A.U., Dw5000 m, and lambdaw1
       m) to the  transition  from "Type I" to "Type II" (w2x10exp24  W/Hz,
       Rw0.4 A.U., Dw10 m, lambdaw1 mm).
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Jennifer Murdoch
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« Reply #23 on: February 04, 2010, 01:23:04 pm »

  Lemarchand and Sagan (1993) also presented a detailed description of
       the expected signal  characteristics,  as well as the most favorable
       positions in the sky to find one of  these  signals.  They also have
       compared the capability of detection of these transmissions  by each
       present and near future SETI projects.

       Infrared Waves

       There have been  some proposals to search in the infrared region for
       beacon signals beamed at us (Lawton, 1971, and Townes, 1983).
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Jennifer Murdoch
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« Reply #24 on: February 04, 2010, 01:23:14 pm »

       Basically, the higher  gain  available   from  antennas  at  shorter
       wavelengths (up to 10exp14 Hz) compensates for the higher quantum
       noise in the   receiver   and  wider  noise  bandwidth   at   higher
       frequencies.

       One concludes that  for  the  same  transmitter  powers and directed
       transmission which takes advantage of the high gain, the detectable
       signal-to-noise ratio is comparable at 10 micro-m and 21 cm.  Since
       non-thermal carbon dioxide (CO2) emissions have been detected in the
       atmospheres of both Venus and Mars (Demming and Mumma, 1983), Rather
       (1991) suggested the possibility that an advanced society could
       construct transmitters of enormous  power  by orbiting large mirrors
       to create a high-gain maser from the natural amplification  provided
       by the inverted atmospheric lines.
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Jennifer Murdoch
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« Reply #25 on: February 04, 2010, 01:23:25 pm »

An observation program  around three hundred nearby solar-type stars
       has just begun  (Tarter,  1992)   by   Albert  Betz  (University  of
       Colorado) and Charles Townes (University of California at Berkeley).

       These observations are currently being made on one  of  the two 1.7-
       meter elements of an IR interferometer at Mount Wilson observatory.

       On average, 21  hours  of  observing time per month is available for
       searching for evidence of technological signals.

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Jennifer Murdoch
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« Reply #26 on: February 04, 2010, 01:23:38 pm »

Dyson (1959, 1966)   proposed   the   search   for  huge  artificial
       biospheres created around a star by an intelligent species as part
       of its technological growth and expansion within a planetary system.

       This giant structure would most  likely  be  formed  by  a  swarm of
       artificial habitats and   mini-planets   capable   of   intercepting
       essentially all the radiant energy from the parent star.

       According to Dyson  (1966),  the mass of a planet like Jupiter could
       be used to  construct an immense  shell  which  could  surround  the
       central star, having a radius of one Astronomical Unit  (A.U.).  The
       volume of such a sphere would be 4cr2S, where r is the radius of the
       sphere (1 A.U.)  and  S the thickness.  He imagined a shell or layer
       of rigidly built objects Dw10exp6 kilometers in diameter arranged to
       move in orbits  around the star.   The  minimum  number  of  objects
       required to form  a  complete  spherical  shell  [2]  is  about  N=4
       PIrexp2/Dexp2w2x10exp5 objects.
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Jennifer Murdoch
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« Reply #27 on: February 04, 2010, 01:23:50 pm »

This kind of  object,  known  as  a  "Dyson Sphere", would be a very
       powerful source of infrared radiation.   Dyson predicted the peak of
       the radiation at ten micrometers.

       The Dyson Sphere is certainly a grand, far-reaching  concept.  There
       have been some  investigations to find them in the IRAS database (V.
       I. Slysh, 1984;  Jugaku  and  Nishimura,  1991;  and  Kardashev  and
       Zhuravlev, 1992).

       ==================================================================
           2 - The concept of this extraterrestrial construct was first
           described in the science fiction novel STAR MAKER by Olaf
           Stapledon in 1937.
       ==================================================================

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« Reply #28 on: February 04, 2010, 01:24:03 pm »

Optical Waves

       In the radio domain, there have been several proposals  to  use  the
       visible region of  the  spectrum  for  interstellar  communications.
       Since the first proposal by Schwartz  and  Townes  (1961), intensive
       research has been  performed  on  the  possible use  of  lasers  for
       interstellar communication.

       Ross (1979) examined  the  great advantages of using short pulses in
       the nanosecond regime at high energy  per  pulse  at  very  low duty
       cycle.

       This proposal was  experimentally explored by Shvartsman  (1987) and
       Beskin (1993), using a Multichannel Analyzer of Nanosecond Intensity
       Alterations (MANIA), from  the  six-meter telescope in Russia.  This
       equipment allows photon arrival  times  to  be  determined  with  an
       accuracy of 5x10exp(-8)  seconds,  the  dead time being  3x10exp(-7)
       seconds and the  maximum  intensity  of  the incoming photon flux is
       2x10exp4 counts/seconds.
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Jennifer Murdoch
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« Reply #29 on: February 04, 2010, 01:24:13 pm »

In 1993, MANIA  was  used  from  the  2.15-meter  telescope  of  the
       Complejo Astronomico El  Leoncito  in  Argentina, to  examine  fifty
       nearby solar-type stars for the presence of laser pulses (Lemarchand
       et al, 1993).

       Other interesting proposals and analysis of the advantages of lasers

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