Ocean Sound Range 2D: Frequency-Dependent Attenuation

Sound Source Preset

Source Parameters

Frequency 20 Hz

Source level SL 188 dB

Listener range 50 km

Propagation geometry

Live Readouts

Absorption α

0.0 dB/km

Transmission loss

0 dB

Received level RL

0 dB

Detected?

—

Max detection range (RL = 70 dB noise floor)

— km

How it works

Sound weakens with range r for two independent reasons. Geometric spreading loss spreads the same acoustic energy over an ever-larger wavefront:

Spherical (deep water):   TL_spread = 20·log10(r)
Cylindrical (SOFAR duct): TL_spread = 10·log10(r)   (r in metres)

Seawater also absorbs acoustic energy — viscosity plus the relaxation of dissolved boric acid and MgSO₄ molecules turns sound into heat, far more strongly at high frequency. Thorp's empirical formula gives the absorption coefficient α (dB per km) from frequency f in kHz:

α(f) = 0.11·f²/(1+f²) + 44·f²/(4100+f²) + 2.75×10⁻⁴·f² + 0.003

Total transmission loss and received level at range r (km):

TL(r) = TL_spread(r) + α(f)·r
RL(r) = SL − TL(r)

The bottom chart plots RL(r) for four real sources plus your custom frequency, on a shared log-range axis against the ambient ocean noise floor (~70 dB re 1 µPa). Low-frequency curves stay flat for a very long way — a 20 Hz blue-whale call has α of only ~0.001 dB/km — while the 110 kHz dolphin click's curve dives almost immediately, since its α runs above 30 dB/km.

Top panel — a 2D range cross-section: the source pulses expanding wavefronts rightward along a logarithmic range axis, fading in brightness exactly as fast as the computed transmission loss dictates.
Bottom panel — live RL-vs-range curves for all four presets, with your current custom frequency highlighted and the noise floor drawn as a dashed line.
Geometry toggle — cylindrical spreading (SOFAR channel or shallow duct) loses only 10·log10(r), roughly doubling range versus open-ocean spherical spreading.

Outgoing wavefront pulse Listener buoy — detected Listener buoy — below noise floor