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D. Kent Cullers

NASA Ames Research Center

Mail Stop 244-11

Moffett Field, CA 95035-1000



Electromagnetic SETI searches since 1960 have used a variety of search strategies. They have sampled 22 octaves in frequency with widely different sensitivities and sky coverages. Searches used a variety of detection bandwidths and data processing techniques, and consequently, the signals to which they were best matched differed greatly. Since the methods of extraterrestrial signaling are unknown, one cannot be certain of the relative merit of SETI searches. However, under plausible assumptions about the distribution of signal parameters, it is possible to evaluate all prior and proposed searches.

If frequency and space are assumed to be uniformly populated with signals, the probability of detecting a signal increases with frequency coverage, sky coverage, and sensitivity. If number of signal types is also considered, search merit depends upon the assumed distribution of signal parameters. Increases in computing power allows simultaneous matching to more signal types, thus enhancing the probability of search success or search merit. The approach presented here assesses search merit under assumptions of either uniform or logarithmic distribution of signaling parameters such as pulse length. Under both assumptions, NASA's radio search is the most powerful to date. This is due to its high sensitivity, obtained at the cost of large computational load, and extensive frequency and sky coverage for many signal types.

It may be possible to construct optical searches in the future which will have comparable merit. Such searches, though less sensitive with present technology, cover very large amounts of frequency compared to all radio searches conducted so far. Certainly, such searches will explore a new electromagnetic domain.


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