Overview
ISO 17208-2:2019 - "Underwater acoustics - Quantities and procedures for description and measurement of underwater sound from ships - Part 2" defines methods to convert deep-water radiated noise level (RNL) measurements into an equivalent monopole source level. The standard provides procedures for direct calculation from deep-water measurements with a specified hydrophone geometry and prescribes reporting of the nominal source depth and broadside aspect source level. The conversion accounts for surface reflections (the Lloyd’s mirror effect) and is intended to supply monopole source data for long-range sound propagation models and environmental assessments.
Key technical topics and requirements
- Scope: Conversion of RNL (measured per ISO 17208-1) to an equivalent monopole source level for broadside only, with the nominal source depth reported alongside the value.
- Measurement geometry: Deep-water measurements use three vertically arranged hydrophones positioned to sample depression angles of 15°, 30° and 45° at the closest point of approach (CPA). CPA distance is 100 m or one ship length, whichever is greater (per ISO 17208-1).
- Nominal source depth: Defined as 0.7 × ship draft; this single depth is used for the monopole conversion and must be reported.
- Conversion method: Uses an averaged RNL correction (ΔL) derived from formulas that incorporate the Lloyd’s mirror effect (surface pressure-release reflection). Annex A provides derivation and alternative formulations; Annex B covers corrections for deviations from ISO 17208-1 geometry.
- Frequency bands: One-third-octave bands (base 10) as per IEC 61260-1 are used for spectral calculations.
- Uncertainty: Combined expanded uncertainties for RNL (from ISO 17208-1) are provided as typical values:
- Low frequency (10–100 Hz): ≈ 5 dB
- Mid frequency (125 Hz–16 kHz): ≈ 3 dB
- High frequency (>20 kHz): ≈ 4 dB
Additional uncertainties arise from the conversion formula and the monopole approximation.
Practical applications and users
ISO 17208-2:2019 is used by:
- Marine acoustics laboratories and field measurement teams performing deep-water ship noise surveys
- Environmental consultants and researchers assessing underwater noise impacts on marine life
- Shipping companies and classification societies compiling noise inventories or demonstrating compliance with guidance from IMO/MEPC
- Modelers who require monopole source input for long-range propagation and impact modelling
Typical applications:
- Converting ship radiated noise measurements to source levels for propagation modelling
- Environmental impact assessments for shipping routes and port operations
- Creation of standardized ship noise databases for regulatory or research use
Related standards
- ISO 17208-1:2016 - Requirements for precision measurements in deep water (measurement procedure and RNL definition)
- ISO 18405 - Underwater acoustics terminology
- IEC 61260-1 - One-third-octave and fractional-octave band specifications
Keywords: ISO 17208-2:2019, underwater acoustics, radiated noise level, monopole source level, deep water measurements, Lloyd’s mirror, hydrophone geometry, nominal source depth, measurement uncertainty.
Open preview (PDF)Underwater acoustics — Quantities and procedures for description and measurement of underwater sound from ships — Part 2: Determination of source levels from deep water measurements
