Atmosphere

The atmosphere module contains functions and classes related to atmospheric acoustics and is based on acoustics.standards.iso_9613_1_1993.

Atmosphere class

class acoustics.atmosphere.Atmosphere(temperature=293.15, pressure=101.325, relative_humidity=0.0, reference_temperature=293.15, reference_pressure=101.325, triple_temperature=273.16)

Class describing atmospheric conditions.

REF_PRESSURE = 101.325

International Standard Atmosphere in kilopascal

REF_TEMP = 293.15

Reference temperature

TRIPLE_TEMP = 273.16

Triple point isotherm temperature.

__init__(temperature=293.15, pressure=101.325, relative_humidity=0.0, reference_temperature=293.15, reference_pressure=101.325, triple_temperature=273.16)

Parameters:

• temperature – Temperature in kelvin
• pressure – Pressure
• relative_humidity – Relative humidity
• reference_temperature – Reference temperature.
• reference_pressure – Reference pressure.
• triple_temperature – Triple temperature.

attenuation_coefficient(frequency)

Attenuation coefficient \(\alpha\) describing atmospheric absorption in dB/m as function of frequency.

Parameters:frequency – Frequencies to be considered.

The attenuation coefficient is calculated using acoustics.standards.iso_9613_1_1993.attenuation_coefficient().

frequency_response(distance, frequencies, inverse=False)

Frequency response.

Parameters:

• distance – Distance between source and receiver.
• frequencies – Frequencies for which to compute the response.
• inverse – Whether the attenuation should be undone.

impulse_response(distance, fs, ntaps=None, inverse=False)

Impulse response of sound travelling through atmosphere for a given distance sampled at fs.

Parameters:

• atmosphere – Atmosphere.
• distance – Distance between source and receiver.
• fs – Sample frequency
• ntaps – Amount of taps.
• inverse – Whether the attenuation should be undone.

See also

impulse_response()

molar_concentration_water_vapour

Molar concentration of water vapour \(h\).

The molar concentration of water vapour is calculated using acoustics.standards.iso_9613_1_1993.molar_concentration_water_vapour().

plot_attenuation_coefficient(frequency)

Plot the attenuation coefficient \(\alpha\) as function of frequency and write the figure to filename.

Parameters:

• filename – Filename
• frequency – Frequencies

Note

The attenuation coefficient is plotted in dB/km!

pressure = None

Ambient pressure \(p_a\).

reference_pressure = None

Reference pressure.

reference_temperature = None

Reference temperature.

relative_humidity = None

Relative humidity

relaxation_frequency_nitrogen

Resonance frequency of nitrogen \(f_{r,N}\).

The resonance frequency is calculated using acoustics.standards.iso_9613_1_1993.relaxation_frequency_nitrogen().

relaxation_frequency_oxygen

Resonance frequency of oxygen \(f_{r,O}\).

The resonance frequency is calculated using acoustics.standards.iso_9613_1_1993.relaxation_frequency_oxygen().

saturation_pressure

Saturation pressure \(p_{sat}\).

The saturation pressure is calculated using acoustics.standards.iso_9613_1_1993.saturation_pressure().

soundspeed

Speed of sound \(c\).

The speed of sound is calculated using acoustics.standards.iso_9613_1_1993.soundspeed().

temperature = None

Ambient temperature \(T\).

triple_temperature = None

Triple temperature.

From ISO 9613-1 1993

Constants

iso_9613_1_1993.SOUNDSPEED = 343.2

iso_9613_1_1993.REFERENCE_TEMPERATURE = 293.15

iso_9613_1_1993.REFERENCE_PRESSURE = 101.325

iso_9613_1_1993.TRIPLE_TEMPERATURE = 273.16

Functions

acoustics.standards.iso_9613_1_1993.soundspeed(temperature, reference_temperature=293.15)

Speed of sound \(c\).

Parameters:

• temperature – Ambient temperature \(T_0\)
• reference_temperature – Reference temperature \(T\)

The speed of sound is calculated using

\[c = 343.2 \left( \frac{T}{T_0} \right)\]

acoustics.standards.iso_9613_1_1993.saturation_pressure(temperature, reference_pressure=101.325, triple_temperature=273.16)

Saturation vapour pressure \(p_{sat}\).

Parameters:

• temperature – Ambient temperature \(T\)
• reference_pressure – Reference pressure \(p_r\)
• triple_temperature – Triple point temperature water \(T_{01}\)

The saturation vapour pressure is calculated using

\[p_{sat} = 10^C \cdot p_r\]

with exponent \(C\) given by

\[C = -6.8346 \cdot \left( \frac{T_{01}}{T} \right)^{1.261} + 4.6151\]

acoustics.standards.iso_9613_1_1993.molar_concentration_water_vapour(relative_humidity, saturation_pressure, pressure)

Molar concentration of water vapour \(h\).

Parameters:

• relative_humidity – Relative humidity \(h_r\)
• saturation_pressure – Saturation pressure \(p_{sat}\)
• pressure – Ambient pressure \(p\)

The molar concentration of water vapour is calculated using

\[h = h_r \frac{p_{sat}}{p_a}\]

acoustics.standards.iso_9613_1_1993.relaxation_frequency_nitrogen(pressure, temperature, h, reference_pressure=101.325, reference_temperature=293.15)

Relaxation frequency of nitrogen \(f_{r,N}\).

Parameters:

• pressure – Ambient pressure \(p_a\)
• temperature – Ambient temperature \(T\)
• h – Molar concentration of water vapour \(h\)
• reference_pressure – Reference pressure \(p_{ref}\)
• reference_temperature – Reference temperature \(T_{ref}\)

The relaxation frequency of nitrogen is calculated using

\[f_{r,N} = \frac{p_a}{p_r} \left( \frac{T}{T_0} \right)^{-1/2} \cdot \left( 9 + 280 h \exp{\left\{ -4.170 \left[ \left(\frac{T}{T_0} \right)^{-1/3} -1 \right] \right\} } \right)\]

acoustics.standards.iso_9613_1_1993.relaxation_frequency_oxygen(pressure, h, reference_pressure=101.325)

Relaxation frequency of oxygen \(f_{r,O}\).

Parameters:

• pressure – Ambient pressure \(p_a\)
• reference_pressure – Reference pressure \(p_r\)
• h – Molar concentration of water vapour \(h\)

The relaxation frequency of oxygen is calculated using

\[f_{r,O} = \frac{p_a}{p_r} \left( 24 + 4.04 \cdot 10^4 h \frac{0.02 + h}{0.391 + h} \right)\]

acoustics.standards.iso_9613_1_1993.attenuation_coefficient(pressure, temperature, reference_pressure, reference_temperature, relaxation_frequency_nitrogen, relaxation_frequency_oxygen, frequency)

Attenuation coefficient \(\alpha\) describing atmospheric absorption in dB/m for the specified frequency.

Parameters:

• pressure – Ambient pressure \(T\)
• temperature – Ambient temperature \(T\)
• reference_pressure – Reference pressure \(p_{ref}\)
• reference_temperature – Reference temperature \(T_{ref}\)
• relaxation_frequency_nitrogen – Relaxation frequency of nitrogen \(f_{r,N}\).
• relaxation_frequency_oxygen – Relaxation frequency of oxygen \(f_{r,O}\).
• frequency – Frequencies to calculate \(\alpha\) for.