It would be desirable to conduct the analysis of cosmic radio waves along the following lines: examination of the shape of the radio spectrum as a whole for envelopes and carrier waves; inspection of the fine structure of the spectrum; recordings of rapid variability of the carrier and envelope spectra; establishment of the carrier and envelope distribution functions; determination of how the polarization (especially circular polarization) depends on the carrier frequency and on time; investigation of recordings obtained by analog and digital detection of carriers and envelopes at different frequencies and bands for both.

The data obtained in this manner would be used to identify sources suspected of being artificial. The methods and criteria for identification should include an analysis of all data from the standpoint both of astrophysics (comparison with known and possible natural astrophysical objects) and cybernetics and information theory (comparison of the statistical properties and structure of the signal with known or anticipated types of communication).

3. INSTRUMENTATION PROJECTS FOR SEEKING RADIO SIGNALS FROM EXTRATERRESTRIAL CIVILIZATIONS

To ensure that the avenues of research described above will be carried out, two instrumentation projects, CETI 1 and CETI 2, are proposed, as follows.

CETI 1 Project (1975-1985)

1. A ground-based system continuously monitoring the entire sky, comprising eight stations with nondirectional antennas supported by detection equipment capable of covering the whole optimum wavelength range.

2. A satellite system continuously monitoring the entire sky, comprising two space stations with nondirectional antennas and fully covering the optimum wavelength range.

3. A system of low-directivity antennas of 1-3° beamwidth for a continuous survey of nearby galaxies (subsection 1.5). These antennas might conveniently be located at the same stations where the sky is continuously monitored by nondirectional antennas.

CETI 2 Project (1980-1990)

1. A satellite system continuously monitoring the entire sky and equipped with antennas of large effective area.

2. A system of two widely spaced stations having large (effective area ≈ 1 km2) semirotatable antennas for synchronized reception, searches for signals from specific objects, and analysis of selected sources.

These instrumentation complexes could be used not only for CETI work but for a variety of important astrophysical problems.

In addition, individual parts of the program could be carried out with other radio telescopes in conjunction with the plans of radio-astronomy institutions (sky surveys, investigations of peculiar sources, and so on).

PART III

DECODING OF SIGNALS

One of the most important problems in need of solution for CETI purposes is to work out deciphering techniques specifically applicable to extraterrestrial communications (in the absence of any a priori information as to the language, method of encoding, and character os the signals). Within the present program a leading role should be assigned to logically formal deciphering techniques, comprising algorithms that can be implemented only by computer, and enabling a given linguistic entity to be designated according to a maximum of special "estimator" functions computed from counts made on the test being analyzed. The decoding procedure for signals from extraterrestrial civilizations that is to be developed as part of this program may be broken down into several steps.

1. Preliminary analysis of signals. In this step the alphabet of the elementary signals (messages) would be established.

2. Determination of type of text language organization. Three types of organization are presumably possible: pictorial (image transmission), linguistic (analogous to the structure of languages on the earth), and formalized (as with logical computer languages or algorithms).

3. Disclosure of grammatical system of the language. The properties of the test explained by the internal structure of the language would be ascertained at this stage, that is, the parametrization of the frames and alphabetic gradations used to express model languages. The grammar of a humanoid language would be determined, or for formalized systems, the axioms and rules of construction and derivation.

4. Disclosure of the semantics of texts under investigation.

5. Development of methods for translating the decoded language into familiar languages. This step would, in particular, encompass techniques for automatic compilation of bilingual dictionaries and structural correspondence lexicons.

The development of signal decoding techniques is closely related to research on image recognition, automatic classification and encoding (for example, some of the algorithms worked out in the decipherment analysis might be applied to study the structure of branches of the national economy), and work in the area of computer translation and automated abstracting.

PART IV

CONCLUSION

Even in their initial stage investigations of the CETI problem can be of important cognitive and applied value, and can serve as a source of useful information and a stimulus in many fields of science and technology.

This working program, which includes experimental and theoretical projects of immediate concern, is provisionally directed toward the next 10-15 years. It should form part of a more complete program taking the long view, and it also offers a basis for developing specialized, detailed programs in particular areas of research that fall within the scope of the CETI problem.

Continual revision and improvement should be made in the program as data are accumulated in all fields pertaining to CETI and as individual search programs are conducted.

REFERENCES

1Project Cyclops: A Design Study of a System for Detecting Extraterrestrial intelligent Life (NASA-CR-114445), Stanford Univ. and NASA Ames Res. Cen., Moffett Field, Calif. (1972).

2G. M. Tovmasyan, ed., Extraterrestrial Civilizations (Proc. Byurkan conf., May 1964), Armenian Acad. Sci. Press (1965) [Israel Program Sci. Transl., No. 1823 (1967)].

3C. Sagan, ed., Communication with Extraterrestrial Intelligence (CETI) (Proc. Byurakan conf., Sept. 1971), MIT Press (1973).

*S. A. Kaplan, ed., Extraterrestrial Civilizations: Problems of Interstellar Communication, Nauka, Moscow (1969) [NASA TT F-631 (1971)].

12. SEARCHES TO DATE

In addition to on-going radioastronomical observations, there have been several deliberate attempts to detect signals of extraterrestrial intelligent origin, all with negative results. In most cases, only a few select objects have been observed, at a few discrete frequencies using relatively wide bandwidths and at only moderate to low sensitivities. Although most laudable, these observations require enormous equivalent isotropic radiated power on the part of other civilizations to be detectable.

13. THE MAINTENANCE OF ARCHIVES

Rational search by humankind through a hyperspace of the size and complexity contemplated here requires systematic compaction and storage of the results as they come in. Uncommon care should be exercised in deciding what data to discard. In the near future, a plan should be prepared for a relatively long-lasting storage procedure, one providing easy access to the stored data, not only to colleagues in the search, but also to others who have an interest for any variety of reasons. Its construction will require careful thought, some experience, and recognition that this data bank has enormous growth potential. Probably, such a plan would itself grow through a number of stages in response to comments following dissemination of a preliminary plan.

It is attractive to suppose some appropriate journal would publish the plan and its development, and perhaps continue with periodic reports of the results to date in summary form, with clear information on how to gain the full details. The initial publication should be co-authored by representatives of several of the groups in the field. The Byurakan-founded international CETI committee could easily serve to invite such attention.

The magnitude of the permanent data storage problem presented by an extensive, state-ofthe-art SETI installation is worth illustration. Consider just the preposed receiver - 300 MHz instantaneous bandwidth; 1 Hz frequency resolution (bin width); 6 polarization channels; and 16 bits per output bin per second; 100 sec per target direction (for 100 unit observations). Thus there will be approximately 3X1012 bits to be disposed of every 100 sec. A large fraction of this torrent of data is redundant, since it is just plain noise. Sorting and compacting routines are an economic necessity for all recognizable spectral structures 2 or 3 sigma above the mean noise level. Then, the remainder of the data must be discarded.

What should be saved for future reference? Here is a partial list:

1. Housekeeping data when, by whom, with what installation; circumstances of the observation; essential system parameters, etc.

2. Identified (interfering) coherent signals - general characteristics (frequency, drift rates, bandwidth, etc.).

3. Unidentified coherent signals - general characteristics and estimated nature.

4. Astrophysical data continuum radiation as a function of frequency; a wealth of (primarily) interstellar line profiles; variable or intermittent radiations (pulsars, etc.); etc.

5. Pattern recognition and compaction algorithms in operation.

6. Comments by observers.