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Nobeltec InSight Radar (IR2)
Operations Manual
Radar Horizon
The radio waves used for radar are called microwaves, and like light, they travel
in straight lines. Because light is generally refracted toward the ground surface,
we are able to see farther than the physical horizon. This is called the optical
horizon as compared to the physical horizon. Otherwise, microwaves have similar
characteristics to light, and this is called a radar horizon. Since microwaves are
longer than light in terms of wavelength, the radar horizon is farther than the optical
horizon by about 6% and the physical horizon by about 15%. The radar horizon
changes according to the radar transceiver height and target height.
Radar Horizon and Mother Nature
As temperature and humidity change in the air, the refractive index of radar radio
waves change, consequently causing the detectable range of the radar to vary. This
gives us a variation of detectable range due to a change in ambient conditions
Sub-refraction
When cold air flows over the warm surface, the radar waves are curved upwards.
This phenomenon is called sub-refraction. As a result, the detectable range of the
radar is reduced. This is likely to occur in polar regions, or in warm currents where
cold air from the polar regions flow into the sea.
Super-refraction
When the air being warmed up inland flows in the cold sea, radio waves are curved
downward. This is called super-refraction. In this case, the range of the radar
increases. This phenomenon is apt to be produced in the warm coastal regions,
and becomes noticeable as the temperature difference becomes larger.
Understanding Radar
