Have you ever been scared by a radar gun being pointed at you by traffic police officers even as you speed? Have you been fascinated by the variation of sound waves’ frequency when a vehicle sounding a siren approaches, passes you by and then recedes? Either way, these fascinating phenomena where you detect differences in wave frequency of moving objects form the basis for understanding how a Doppler radar works.
Radar is any system that sends radio waves, shows the location, and returns to be detected by this same machine. The differences in variations between observed and emitted frequencies help determine an object’s location, speed, direction, and distance. A useful application of radars is in the detection and tracking of aircraft. Doppler radars are also excellent in the tracking of submerged objects underwater in submarines by using sound waves.
A simple comprehension of the Doppler effect and its applications is crucial in understanding how the Doppler radar works. And that’s the goal this article aims to achieve.
The meaning of Doppler radar
A Doppler radar is a unique type of radar that utilizes the Doppler effect to determine an object’s location, speed, and direction from a distance. The Doppler radar achieves this by sending microwave signals to the target object at a distance. The rate at which the direction and velocity of this moving object will alter the return signal’s frequency will provide accurate and precise measurements of the object’s radius in relation to the radar.
In layman’s terms, a Doppler radar is simply a radar used to determine a target object’s speed from a distance.
In part because of its everyday use by weather forecasters on television in weather reporting, the term “Doppler Radar” has been mistakenly very similar to the type of radar used in weather forecasts. Most modern climate uses the pulse-Doppler process to monitor rainfall movements, but it is merely part of processing their data. Therefore, while these radars use a particular type of Doppler radar, the term is extensive in its meaning and use.
What is the Doppler effect?
Whereas it might not be easy to figure out how different radars work, the simple comprehension of the Doppler effect would understand how Doppler radar works easier.
The Doppler effect was named in 1842 after an Austrian physicist Christian Doppler. The Doppler effect is the difference between the optical frequency and the spectator wave’s output frequency to the wavelength.
Examples of Doppler effect at work:
- The Doppler effect is often heard as an approaching car sounds a siren, passes by, and recedes from the onlooker. The frequency obtained is higher (compared to the output frequency) when the car is approaching, the same as the moment it’s passing by, and lower the further it moves away from the onlooker.
- This frequency variation depends on the direction of the target object concerning the viewer; it is high when the wave source moves directly or away from the viewer and decreases with an increasing angle between the direction of movement and the direction of the waves until the source moves to the right level for the observer, there is no change.
- Additionally, try to imagine yourself throwing a tennis ball every second at your buddy at the same rate. Your buddy is likely to have an easy time catching the balls because of constant frequency. However, when you start jogging towards your friend as you throw balls simultaneously and at the frequency of one ball every second, your friend will get overwhelmed because he catches the balls more frequently. It’s because the balls are less spaced out.
On the contrary, when you start moving away from him, he’ll catch balls less frequently because they’re more spaced out; thus, the frequency decreases. While from your perspective, the frequency of throws is constant, the relative velocity difference between you and your friend gives rise to the Doppler effect.
How exactly does the Doppler radar work?
As mentioned earlier, the Doppler radar is a unique radar used to determine the speed, direction, and location of an object using radio waves.
Doppler radar operates using the information that the waves generated by the object will be compressed in close proximity as it approaches you or spaced out the further it moves away from you. That is the same reason why the police siren sounds become low-pitched as their cargoes farther away from you. As the sound waves are emitted, as the car moves farther away from you, the waves’ distance increases and thus are spaced farther out.
However, as the car approaches you, it tends to catch up with the previous sound waves it produced. The closer to you it gets, the more it squashes the sound waves together. Compressed sound waves have a higher frequency. And higher frequency sound waves have a higher pitch. On the other hand, sound waves that are spread out farther have are low-pitched.
Therefore, the closer a car gets to an onlooker, the more the sound waves are compressed, thus the higher the pitch of the siren. On the contrary, the farther away from the cargoes from the same onlooker, the farther out the sounds waves are spread. Thus, the low-pitched the siren gets. The Doppler radar operates just the same way as the police car siren.
Doppler radar uses
- If you’ve ever wondered what speed cameras on highways are for, this article might save you from the legal ramifications of a speeding ticket. Regardless of how fast you accelerate past a speed camera, it’ll take a picture of your car, and you’ll get a speeding ticket. Its purpose is to send out radio waves to speeding vehicles to calculate their speeds.
- Additionally, if you’ve gotten scared by traffic police officers pointing a radar gun in your direction, it works the same way. The signals that are returned to the radar gun help them determine whether you’re driving within the speed limit.
- Moreover, the Doppler radar is crucial in the tracking of aircraft in aviation.
- Last but not least, the usage of a Doppler radar in metrology cannot be overemphasized. Here, they use the pulse-Doppler technique to figure out all precipitation processes.
The bottom line
In conclusion, a Doppler radar works the same way a police car siren does. Its objective is to figure out the speed, direction, and location of a target object from a distance. It achieves this purpose by sending microwave signals to a specific object at a distance. By analyzing the frequency at which the object has altered these returned wave signals in motion, we can tell the object’s velocity.
The Doppler radar applications cannot be exhausted across the aviation, metrological, and medical industries, to mention a few.