EIRP (Equivalent / Effective Isotropic Radiated Power) is the standard metric used in radio SETI and technosignature searches to express transmitter detectability. It is the power that a hypothetical isotropic (omnidirectional) transmitter would need to radiate to produce the signal a search could detect at a given distance. A survey’s EIRP upper limit therefore states the weakest beacon that survey could have ruled out — lower limits mean a more sensitive search.
Why it matters
- EIRP lets searches with different telescopes, frequencies, distances, and integration times be compared on a common footing, since raw flux limits alone don’t capture how far away or how powerful a putative transmitter is.
- For reference scale: a planetary-radar transmitter like Arecibo had an EIRP of roughly 10¹³ W; a Kardashev Type I civilization commanding its planet’s power budget could in principle exceed 10¹⁷ W.
Vault appearances
- The Sardinia Radio Telescope high-frequency survey set an EIRP limit of 1.8×10¹⁹ W over ~5×10⁵ stars toward the Galactic Center (src-sardinia-technosignature-search-2026-05).
- By contrast, the ATLAS constrained transmitter power to as low as ~2.9×10⁻³ W — vastly tighter because the target was astronomically close.