How Does Doppler Radar Work

A Doppler radar is an instrument, used to measure the velocity and direction of a moving object. The radar was invented for the first time in 1904 by Christian Hülsmeyer, while detecting a distant ship in a foggy climate. However, one major drawback of the radar was the inability to estimate the distance of the object. In the early 1940s, the modern version of Doppler radars were discovered.

There are many types of Doppler radars such as Continuous Wave, Coherent Pulsed, etc. The basic principle behind the working of a Doppler radar is to measure the radial velocity of the echoes, that are generated from the target areas. Doppler radars are used in several aspects of life, some of which are, satellite sounding, weather forecasting, traffic surveillance, military services, air traffic control and radiology. Following is a brief discussion on how a Doppler radar works.

How Does Doppler Radar Work

While speaking about the working of a Doppler radar, there are two basic phenomena that are being used, viz., the Doppler effect and the radar. The Doppler effect, discovered by Christian Doppler, an Austrian scientist, in 1942, is the process by which the wave frequency for an observer changes with respect to the direction of movement of the waves source.

In case of waves, that travel in a medium (for example, sound waves), the overall Doppler effect depends on the motion of the source, medium and the observer. In case of waves without a medium (for example, light), only the velocity difference between the observer and the source is taken into consideration.

Radars, on the other hand, are systems that make use of transmitters for generating electromagnetic waves, either microwaves or radio waves. These waves after landing on objects, are reflected back in the same direction of the transmitter. The transmitter then, perceives the reflected waves. Though the reflected signals are generally weaker than the generated waves, they can be amplified and/or displayed by means of sophisticated machines. Thus, radars can detect objects (either stationary or moving), which are located in far-off areas.

Doppler radars are the best equipments used for detecting rainfall and/or forecasting weather of a particular area. While detecting rainfall, the Doppler radar sends out radio waves from the antenna, which are reflected back to the transmitter. The frequency of the reflected radio waves depends on whether the object(s) (for example, cloud, raindrops, hailstones) is moving away from the antenna or towards the antenna. In the former case, the frequency will be low; whereas, in the latter case, the frequency will be high.

Whatever may be the outcome of the reflected frequency, all weather radars are installed with equipments that effectively convert the radio waves into pictures, displaying the position, intensity of precipitation and even, a change in wind direction. The location of the objects are calculated by determining the time required for the waves to bounce back in the transmitter. This way, the Doppler radar is able to predict the possibility of rain or in short, weather.