range2tl

Compute underwater sound transmission loss from range

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Syntax

tl = range2tl(rng,freq,depth)

Description

tl = range2tl(rng,freq,depth) returns the transmission loss, tl, for a sound wave of frequency freq arriving from a source at distance rng. The channel depth is depth. The transmission loss is due to geometrical spreading and frequency-dependent absorption. This function is the inverse of tl2range.

example

Examples

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Open Live Script

Find the transmission loss (in dB) for a sonar operating at 2 kHz in a channel that is 200 m deep. The sound path is 1000.0 m long.

rng = 1000.0;
freq = 2000.0;
depth = 200;
tl = range2tl(rng,freq,depth)
tl = 
50.1261

Input Arguments

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Distance from sound source to receiver, specified as a positive scalar. Units are in meters.

Example: 10e3

Data Types: double

Frequency of sound, specified as a positive scalar. Units are in Hz.

Example: 1e3

Data Types: double

Channel depth, specified as a positive scalar. The transition range from spherical to cylindrical spreading loss is one-half the channel depth. Units are in meters. The average depth of the ocean is 2000 m.

Example: 2000

Data Types: double

Output Arguments

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Transmission loss, returned as a positive scalar. Units are in dB.

Data Types: double

Algorithms

  • The range2tl and tl2range functions model three sources of transmission loss in an underwater sound channel.

    • Absorption due to relaxation effects for boric acid and magnesium sulfate. Absorption is an important mechanism for frequency-based attenuation – the higher the frequency, the greater the absorption. Relaxation effects depend on seawater salinity (S). alkalinity (pH), and temperature (T). The model assumes constant seawater salinity of 35 ppt (parts per thousand), pH of 8, and water temperature of 10°C throughout the sound channel.

    • Wave damping and intensity loss caused by shear and bulk viscosity of pure water.

    • Geometric spreading loss. For ranges less than or equal to the transition range, the transmission loss is due to spherical spreading. For ranges greater than the transition range, the transmission loss is due to cylindrical spreading. Spherical spreading loss occurs when there are no boundaries (such as the water surface or sea floor) to reflect the acoustic energy. All of the acoustic energy spreads out isotropically in all directions from the source. The loss in intensity is proportional to the surface area of a sphere – the intensity decreases as the inverse square of the range for spherical spreading, TL = 20log(R), where R is the range. Alternatively, cylindrical spreading occurs when there are boundaries in the water column such as the water surface or bottom surface. The loss in intensity is proportional to the surface area of the cylinder – the intensity decreases as the inverse of the range TL = 10log(R), The transition range depends on the location of the source and the water depth. If the source is located halfway between the surface and bottom, it is reasonable to set the transition range to one-half the water columns depth. At this range, the surface of the sphere will just touch the bottom floor and the top surface. A good value for the transition range is 1000 m, since the average ocean depth is about 2000 m.

  • The transmission loss model used is valid for frequencies up to and including 2.0 MHz.

References

[1] Ainslie M. A. and J.G. McColm. "A simplified formula for viscous and chemical absorption in sea water." Journal of the Acoustical Society of America, Vol. 103, Number 3, 1998, pp. 1671--1672.

[2] Urick, Robert J. Principles of Underwater Sound, 3rd ed. Los Altos, CA:Peninsula Publishing, 1983.

Extended Capabilities

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Version History

Introduced in R2017b

See Also

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