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Atmospheric Absorption
Figure 1: Atmospheric absorption
Atmospheric absorption losses consist of an atmospheric basic absorption as well as a strongly weather-dependent auxiliary absorption by fog and rain. The electromagnetic waves are weakened when penetrating air and water vapor layers. In this process mainly water vapor and diatomic oxygen are involved. A part of the electromagnetic energy is converted into heat, another part becomes scattered due to the molecular dipole function.
The diagram shows that the absorption increase as the rates of humidity rises. Furthermore, absorption increases with higher transmitter frequency.
Also, one can see that all frequencies are not equally suitable for all radar applications (e.g., a high frequency is not suitable for long range radars). The very strong absorption at about 75 gigahertz's caused by the oxygen molecules practice the radar-based Pre-Safe Brake Assist Plus developed by Mercedes. The maximum range of the radar is limited on the desired measure by this and mutual disturbing influences therefore are to avoided.
In summary atmospheric absorption losses are always present and cannot be avoided.
Figure 1: Atmospheric absorption
