Quarterly Hydrophone Catalog Update — North Pacific Sector, Q1 FY26
Standard catalog update. Bloop-class events down 4%. One new persistent source (MAR-26-013) noted for review.
FROM:
ASD-4 Cataloging Cell (J. Reyes, lead)
TO:
Distribution List ASD-Q (incl. NEW-3, PAC-2, ABYSS-1)
RE:
Quarterly Hydrophone Catalog Update, North Pacific Sector, Q1 FY26 (01 Jan – 31 Mar 2026).
Summary
Catalog ingest for Q1 FY26 is complete. Of 41,118 candidate events flagged by the auto-classifier across the Pacific SOSUS-equivalent grid and the IUSS littoral overlay, 38,902 were resolved to known taxonomic, geologic, or anthropogenic sources within the standard 14-day review SLA.
Of the remaining 2,216 unresolved events:
| Class | Count | Δ vs. Q4 FY25 |
|---|---|---|
| Bloop-class (broadband, >50 s, sub-20 Hz fundamental) | 71 | −4.1% |
| Slow-Down-class (descending glide, ≥7 min) | 12 | −16.7% |
| Upsweep-class (cyclic, harmonic) | 311 | +1.0% |
| Train-class (regular pulse, 0.8–1.4 Hz) | 1,802 | +0.3% |
| Unclassed persistent | 20 | +1 |
Items for analyst review
Nineteen of the twenty unclassed-persistent sources are previously catalogued and continue to behave within their established envelopes. They are not addressed further in this product.
MAR-26-013 is new this quarter. Bearing estimates from the Mariana western array place the source within the Challenger Deep bathymetric basin, ±2.1 km, depth indeterminate. The signal is a low-amplitude narrowband tone at 7.04 Hz, duty-cycled approximately 11 minutes on / 49 minutes off, with no observed drift in frequency or interval across 412 observation hours.
The 60-minute period is noted. The auto-classifier flagged it against the standing watch list for “regularity exceeding natural-source baseline” and routed it here rather than to Geophysics.
The signal does not match any catalogued cetacean, anthropogenic, or tectonic source. It does not match any entry in the legacy Bennewitz acoustic annex (cross-checked 04 Apr). It is not co-located with any declared seabed asset, friendly or otherwise.
[REDACTED — SECTION 4.2.b, sub (iii): co-bearing correlations with non-acoustic collection]
Per standing instruction, MAR-26-013 is logged as PERSISTENT — UNCLASSED — MONITOR and added to the Q2 reacquisition tasking. No further action is requested of the analyst at this time. If the signal ceases, or if the duty cycle shifts by more than 90 seconds in either phase, ASD-4 will issue an out-of-cycle bulletin.
J. Reyes, Lead Analyst Cataloging Cell, ASD-4 14 April 2026
Distribution: standard. Retain per ASD records schedule (7 yr).
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