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gaspl

RF signal attenuation due to atmosphere gaseous absorption

Description

L = gaspl(range,freq,T,P,den) returns the signal attenuation, L, due to atmosphere gaseous absorption.

  • range represents the signal path length.

  • freq represents the signal carrier frequency.

  • T represents the ambient temperature.

  • P represents the atmospheric pressure.

  • den represents the atmospheric water vapor density.

The gaspl function applies the International Telecommunication Union (ITU) atmospheric gas attenuation model [1] to calculate path loss for signals primarily due to oxygen and water vapor. The model computes attenuation as a function of ambient temperature, pressure, water vapor density, and signal frequency.

The function requires that the signal path is contained entirely in a homogeneous environment – temperature T, atmospheric pressure P, and water vapor density den do not vary along the signal path. You can account for the variation of atmospheric parameters with height using the tropopl and atmositu functions in the Radar Toolbox.

The attenuation model applies only for frequencies at 1–1000 GHz.

example

Examples

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Compute the attenuation spectrum from 1 to 1000 GHz for an atmospheric pressure of 101.300 kPa and a temperature of 15C. Plot the spectrum for a water vapor density of 7.5 g/m3 and then plot the spectrum for dry air (zero water vapor density).

Set the attenuation frequencies.

freq = [1:1000]*1e9;

Assume a 1 km path distance.

R = 1000.0;

Compute the attenuation for air containing water vapor.

T = 15;
P = 101300.0;
W = 7.5;
L = gaspl(R,freq,T,P,W);

Compute the attenuation for dry air.

L0 = gaspl(R,freq,T,P,0.0);

Plot the attenuations.

semilogy(freq/1e9,L)
hold on
semilogy(freq/1e9,L0)
grid
xlabel('Frequency (GHz)')
ylabel('Specific Attenuation (dB)')
hold off

Figure contains an axes object. The axes object with xlabel Frequency (GHz), ylabel Specific Attenuation (dB) contains 2 objects of type line.

First, plot the specific attenuation of atmospheric gases for frequencies from 1 GHz to 1000 GHz. Assume a sea-level dry air pressure of 101.325e5 kPa and a water vapor density of 7.5 g/m3. The air temperature is 20C. Specific attenuation is defined as dB loss per kilometer. Then, plot the actual attenuation at 10 GHz for a span of ranges.

Plot Specific Atmospheric Gas Attenuation

Set the atmosphere temperature, pressure, water vapor density.

T = 20.0;
Patm = 101.325e3;
rho_wv = 7.5;

Set the propagation distance, speed of light, and frequencies.

km = 1000.0;
c = physconst('LightSpeed');
freqs = [1:1000]*1e9;

Compute and plot the atmospheric gas loss.

loss = gaspl(km,freqs,T,Patm,rho_wv);
semilogy(freqs/1e9,loss)
grid on
xlabel('Frequency (GHz)')
ylabel('Specific Attenuation (dB/km)')

Figure contains an axes object. The axes object with xlabel Frequency (GHz), ylabel Specific Attenuation (dB/km) contains an object of type line.

Plot Actual Atmospheric and Free Space Attenuation

Compute both free space loss and atmospheric gas loss at 10 GHz for ranges from 1 to 100 km. The frequency corresponds to an X-band radar. Then, plot the free space loss and the total (atmospheric + free space) loss.

ranges = [1:100]*1000;
freq_xband = 10e9;
loss_gas = gaspl(ranges,freq_xband,T,Patm,rho_wv);
lambda = c/freq_xband;
loss_fsp = fspl(ranges,lambda);
semilogx(ranges/1000,loss_gas + loss_fsp.',ranges/1000,loss_fsp)
legend('Atmospheric + Free Space Loss','Free Space Loss','Location','SouthEast')
xlabel('Range (km)')
ylabel('Loss (dB)')

Figure contains an axes object. The axes object with xlabel Range (km), ylabel Loss (dB) contains 2 objects of type line. These objects represent Atmospheric + Free Space Loss, Free Space Loss.

Input Arguments

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Signal path length, in meters, used to compute attenuation, specified as a nonnegative real-valued scalar or vector. You can specify multiple path lengths simultaneously.

Example: [13000.0,14000.0]

Signal frequency in Hz, specified as a positive real-valued scalar, or as an N-by-1 nonnegative real-valued vector or 1-by-N nonnegative real-valued vector. You can specify multiple frequencies simultaneously. Frequencies must lie in the range 1–1000 GHz.

Example: [1.4e9,2.0e9]

Ambient temperature in °C, specified as a real-valued scalar.

Example: -10.0

Dry air pressure in Pa, specified as a positive real-valued scalar. One standard atmosphere at sea level is 101325 Pa.

Example: 101300.0

Water vapor density or absolute humidity, in g/m3, specified as a nonnegative real-valued scalar. The maximum water vapor density of air at 30° C is approximately 30.0 g/m3. The maximum water vapor density of air at 0°C is approximately 5.0 g/m3.

Example: 4.0

Output Arguments

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Signal attenuation in dB, returned as a real-valued M-by-N matrix. Each matrix row represents a different path where M is the number of paths. Each column represents a different frequency where N is the number of frequencies.

More About

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References

[1] Radiocommunication Sector of International Telecommunication Union. Recommendation ITU-R P.676-10: Attenuation by atmospheric gases 2013.

Extended Capabilities

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