Specific attenuation due to atmospheric gases, calculated at
1 GHz intervals, including line centers.
Zenith attenuation due to atmospheric gases, calculated at 1
GHz intervals, including line centers.
Specific attenuation in the range 50-70 GHz at the altitudes
indicated, calculated at intervals of 10 MHz, including line centres (0 km, 5 km,
10 km, 15 km and 20 km).
 Here is the official document by the International
Telecommunications Union (ITU) that contains very detailed data.
ITU-R P.676-13 (08/2022)
Electromagnetic waves are absorbed in the atmosphere according to wavelength.
Two compounds are responsible for the majority of signal absorption: oxygen (O2)
and water vapor (H2O).
The first peak occurs at 22 GHz due to water, and the second at 60 GHz due to
oxygen (see graph at bottom of page). The actual amount of water vapor and oxygen
in the atmosphere normally declines with an increase in altitude because of the
decrease in pressure, so these graphs apply from sea level to around 1 km altitude.
Total attenuation through the atmosphere at any frequency through unobstructed
atmosphere is the sum of free space path loss,
attenuation caused by oxygen absorption and attenuation caused by water vapor absorption.
Rain attenuation, when present adds an additional element. For a chart of sunlight
power density in the visible light and infrared / ultraviolet region of the electromagnetic
spectrum, click here.
AttenTotal = AttenFreeSpacePathLoss + AttenOxygen
+ AttenWaterVapor + AttenRain
The ITU (International Telecommunications Union) publishes a document (ITU-R P.676-13) entitled
"Attenuation by Atmospheric Gases and Related Effects," which contains some complicated
equations and graphs generated from those equations showing atmospheric attenuation.
Three of those are shown at the right side of this page. Unfortunately, the ITU
does not offer a spreadsheet with the data points in a plottable format.
Fortunately (for you), I went to the trouble of extracting the maximum and minimum
attenuation versus frequency points from the "Specific attenuation due to atmospheric
gases, calculated at 1 GHz intervals, including line centres," graph. The original
graph is imported as the background image of an Excel spreadsheet chart, and then
all of the frequency / attenuation coordinates were visually read off the chart
and entered into a data table. Those points were then plotted as shown below.
Atmospheric Attenuation (Specific Absorption) Chart
The above chart was also generated from frequency / attenuation data points picked
off a published graph, and were entered into Excel and plotted.
Posted July 3, 2023
(updated from original post
on 11/20/2013)
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