Atmospheric Radar Wave Absorption

This Demonstration computes radar wave absorption (dB/km) at microwave frequencies in the range 0.1 GHz to 100 GHz, at elevations above ground level from 0 to 30000 m in steps of 5000 m. These computations are performed assuming a standard atmosphere of temperature, pressure, and water vapor density as a function of altitude. Absorption of propagating radar waves is greatest at 22 GHz and 60 GHz due to absorption by water vapor molecules (22 GHz) and by oxygen molecules (60 GHz). For a fixed frequency, absorption is less at higher elevations than at lower elevations.

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DETAILS

The computations in this Demonstration are based on [1]. The two molecules that absorb radar energy in the 0.1 GHz to 100 GHz range are water vapor and oxygen. Water vapor is resonant at 22 GHz, oxygen at 60 GHz, but there are closely spaced resonances over the 50 to 70 GHz band. Of the two, oxygen is the greater absorber. There is an additional oxygen resonance at 120 GHz but its effect is not significant at frequencies below 100 GHz.
Reference
[1] L. V. Blake, Radar Range-Performance Analysis, Silver Spring, MD: Munro Publishing Company, 1991.

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