Reference

Glossary

A working glossary of the terms, units, and designations used across the Laboratories' catalog, publications, and field records.

Baseline: The separation between two recording stations. A long baseline is what lets the Laboratories treat a coincident detection as real: a signal recorded at two widely separated points in the same instant cannot be a fault local to either one.

Calder Ridge carrier: The informal name for FA-0447, a persistent narrow-band signal near 18.633 kHz first logged at the station in 1971 and recurring, on no schedule the Laboratories can account for, ever since. Source undetermined.
Carrier: A persistent, narrow-band signal that holds a stable frequency over time. Most carriers resolve to a known transmitter. A carrier that matches none is what the catalog exists to record.
Class I / II / III: The Laboratories' behavioral taxonomy for detections. Class I: strong, structured, does not repeat. Class II: recurs and holds a stable form. Class III: unresolved -- coincident across stations, or otherwise resistant to every ordinary explanation.
Coincidence: The arrival of the same signal at two or more separated stations in the same instant. The strongest evidence the Laboratories can offer that a detection is genuinely anomalous, and the hardest to explain away.

Distributed Analysis Initiative (DAI): The Laboratories' volunteer distributed-computing program, in which contributed idle computer time performs the bulk of the analysis. Also called the Field Array.

ELF / VLF: Extremely low frequency (roughly 3 to 30 Hz) and very low frequency (roughly 3 to 30 kHz). The bands in which most of the Laboratories' longest-standing detections lie.

FA-####: A Persistent Signal Catalog designation. The number is assigned in order of cataloguing, not of significance.
False-alarm rate: The conservative statistical threshold a candidate must clear to enter the catalog. Set deliberately high; the Laboratories would rather miss a real signal than admit a false one.
Field record: The continuous, archived recording made by an instrument. The Laboratories keep every field record in full, indefinitely, because a recording made before it could be understood may be understood later.

Ground resonance: Persistent low-frequency and sub-audible resonance in the solid earth, the subject of the Terrestrial Resonance Program. Distinct from seismic events; ground resonance persists.

Hydrophone: An underwater microphone. The Laboratories' hydrophone array extends their listening into the deep sound channel, where a low-frequency source can be heard across an ocean basin.

Infrasound: Sound below the threshold of human hearing, under about 20 Hz. Large natural events -- eruptions, bolides -- radiate infrasound that circles the globe.

Narrow-band: Occupying a very small range of frequency. Natural sources are usually broadband; a signal confined to a hair's width of the spectrum is, more often than not, made by something.
Night Watch: The Laboratories' public instrument for browsing the night sky alongside the catalogued celestial detections.
Noise floor: The background level beneath which a signal cannot be recovered. The entire purpose of the Calder Ridge site is to keep it low.

Persistent Signal Catalog (PSC): The Laboratories' standing record of anomalous detections, both their own and the most-studied events in the published literature, classified by behavior.

Quiet zone: A designated area kept free of radio-frequency interference so that faint signals can be recovered. The Calder Ridge tract functions as a private quiet zone; the surrounding low-population region keeps the background exceptionally low.

Recurrence: The return of a catalogued signal. Recurrence is what turns a curiosity into a subject: a signal that comes back can be studied in a way a single event never can.

Sferics: Broadband radio impulses radiated by lightning discharges. A constant feature of the record, and a constant source of candidates that must be rejected.
Sound channel (SOFAR): A layer in the deep ocean that acts as a waveguide, trapping low-frequency sound and carrying it enormous distances with little loss.
Spectrogram: A plot of a signal's frequency content over time. A persistent narrow-band detection appears on one as a single horizontal line that does not fade.

Time standard: The shared, GPS-disciplined clock that stamps every recording. Without a common time standard to better than a fraction of a microsecond, coincidence analysis across stations would be meaningless.