The three most common causes of refraction are water vapor, changes in air temperature, and
changes in air pressure. In an outdoor environment, RF signals typically refract slightly back
down toward the earth’s surface. However, changes in the atmosphere may cause the signal to
bend away from the earth. In long-distance outdoor wireless bridge links, refraction can be an
issue. An RF signal may also refract through certain types of glass and other materials that are
found in an indoor environment. Figure 2.12 show several examples of refraction.