SETI & Technosignatures

Rotational Doppler Cartography Of Technosignatures On Unresolved Planets

By Keith Cowing

Status Report

astro-ph.EP

March 3, 2026

Filed under astro-ph.EP, astronomy, civilization, Doppler drift, Intelligence, radio, SETI, Technosignature

Rotational Doppler Cartography Of Technosignatures On Unresolved Planets — Reconstructed distribution of radio sources on Earth with noise (SNR of 5). Here Earth’s rotation axis is perpendicular to the line of sight as in Fig. 3. Comparing this reconstruction to Fig. 1 shows matching high-population regions. However, because identical signals from a given latitude could originate in either hemisphere, the reconstructed source map is symmetric about the equator, in other words, each actual transmitter appears twice, once in each hemisphere at the same latitude and longitude. In fact, most of the bright spots in the southern hemisphere originate from radio sources located in the northern hemisphere and do not actually exist. The regions that appear bright in the northern hemisphere are, from west to east, the U.S. West Coast, Mexico, Colombia and Venezuela, the U.S. East Coast, Western Europe, the area straddling the Sahara Desert around 20◦ N latitude, West Asia, India, Indonesia, eastern China, and Japan; in the southern hemisphere, the only such region is Brazil. — astro-ph.EP

The discovery of many Earth-like planets has renewed interest in whether life and technological civilizations exist elsewhere.

The Search for Extraterrestrial Intelligence (SETI) seeks evidence for technological civilizations via technosignatures across the electromagnetic spectrum. Here, focusing on artificial radio emissions with extremely narrowband signals, we model Earth as a distant, unresolved source and simulate its narrowband transmissions as observed with current and forthcoming radio facilities.

Planetary rotation induces small but coherent Doppler drifts (maximum fractional shift of order 10−6) that imprint a characteristic, time-varying pattern on the spectrum.

We develop a forward-inverse framework that exploits this modulation: adopting a population-weighted model for terrestrial transmitters, we compute time-resolved spectra and then apply a new inversion method that reconstructs the underlying transmitter distribution from the temporal pattern of fractional frequency offsets.

In noise-added tests, the method recovers the low-order spherical-harmonic structure of the map and retrieves major population centers despite the north-south degeneracy of unresolved observations. The recovered distribution is expected to correlate with continents, climate zones, and population density. This approach moves SETI beyond mere detection, enabling quantitative cartography of a civilization’s activity and inference of host-planet properties through sustained, time-resolved spectroscopy.

Keitaro Takahashi

Comments: 14 pages, 7 figures, accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2603.01032 [astro-ph.EP] (or arXiv:2603.01032v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2603.01032
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Submission history
From: Keitaro Takahashi
[v1] Sun, 1 Mar 2026 10:17:53 UTC (10,871 KB)
https://arxiv.org/abs/2603.01032

Astrobiology, SETI, Technosignature, Astronomy,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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