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# Resonance — SLS-402 (Program MURRELET)

**Public name:** Resonance  **Tracking #:** SLS-402  **Codename:** MURRELET
**Category:** Sensors & Payloads  **Fiscal Year:** FY2025
**Contract award:** 08 December 2024

## Summary

Resonance is the passive acoustic sensing payload — listen-only detection,
classification, and bearing on surface and subsurface contacts. MURRELET is the
"clean" PNW-bird codename (chosen over reused military names), and the payload is
designed to ride either a UUV (SALMON, ROCKFISH) or a moored node. It hears
propeller cavitation long before a radar would paint the contact.

## Notional Capabilities

- Large-aperture coherent hydrophone array; 360° azimuth directional sensing
- Propeller-cavitation and machinery-line detection/classification
- Distributed "PADAL-style" tracking across multiple low-power nodes
- On-board narrowband/broadband processing with false-alarm suppression
- Tracks handed up to ALDER (SLS-305) for fusion with radar/ESM/EO-IR

## Program References

- Makris, N.C., et al., "Fish Population and Behavior Revealed by Instantaneous
  Continental Shelf-Scale Imaging," *Science*, 311:660–663, 2006.
  [doi:10.1126/science.1121756](https://doi.org/10.1126/science.1121756)
- Salish Littoral Systems, *MURRELET: Coherent Hydrophone Arrays for Passive
  Wide-Area Vessel Tracking*, SLS Technical Report TR-402, 2025.
- "Development of Underwater Acoustic Arrays for Passive Detection of Sound
  Sources," *IEEE Journal of Oceanic Engineering*.
  [IEEE 4065747](https://ieeexplore.ieee.org/document/4065747)
- SLS Acoustics Group, *Cavitation-Based Detection and False-Alarm Suppression
  for Autonomous Acoustic Payloads*, SLS White Paper WP-RESONANCE-01, 2025.

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