As we know, it's a disturbing time when Israel and Palestine are undergoing a serious conflict. There have been severe airstrikes and rocket launching attacks. And science plays a vital role in reducing the powerful effects of these attacks and saving many lives. One of the safety measures used by Israel is the Iron Dome, which most have already heard and read about. And being a science student and enthusiast, I thought to share my understanding of the basic science behind the working of this Iron dome.
For those who are not familiar, let me start with a question,
What is an Iron dome?
The iron dome is an effective short-ranged multi-effective air defense system developed by Rafael Advanced Defense Systems, Israel. The system has been designed to counter attacks, short-range rockets and 155mm artillery shell threats with ranges of up to 70km. It can be operated in all weather conditions, including fog, dust storms, low clouds and rain. It has tested a success rate of 90% after intercepting more than 2,000 incoming targets.
Source: https://www.army-technology.com/projects/iron-dome/
How does a RADAR works?
A Radar works using a principle of the Doppler effect. The Doppler effect is the difference in the frequency of a wave leaving a source that reaches an observer due to the relative motion of the source with respect to the observer. To understand it better, we can consider the scenario shown in the picture below.
We have a source (in the picture, the source is a firetruck), which is producing a wave (say sound wave produced by the siren in the fire truck), initially at rest. In this case, the observer will receive a wave with a constant frequency (let's call this frequency f_0). This can be understood from the example of the fire truck, which is at rest initially, producing a sound wave that an observer with a constant pitch hears. Once it starts moving towards the observer (say observer A in the picture), the observer receives the wave, which will have a higher frequency than f_0, or we can say the observer hears the siren with a high pitch. As the truck approaches Observer A, the siren's pitch, keeps increasing until the fire truck reaches Observer A. Once the truck passes the Observer, the pitch gradually decreases.
In such a scenario, the frequency of a wave measured by an observer depends on the velocity of the source (i.e. it depends on how fast the source is moving and the direction of the motion). Suppose we know the speed and frequency of the emitted and received wave, the velocity of the observer and the wave in the medium. In that case, we can calculate the velocity of the moving target relative to the observer.
Basically, two cases show the change in frequency according to the Doppler effect.
- When the target approaches or moves closer to the radar, the wavelength decreases. Thereby increasing the frequency of the signal.
- While in case the target moves away from the radar, an increase in wavelength is noticed, so a decrease in frequency exists.
Then we can find the velocity of the target along the line-of-sight V_r using the equation,
were f_d is the Doppler shifted frequency of the wave that we collect using an antenna. Then the relative velocity in case of moving target is given as:
were \theta is the angular target velocity vector, i.e, the angle between the radar ray and the velocity of the target.
Radar and Iron dome
So the above principle of Radar is used in the Iron dome. The radar in the system is EL/M-2084. This radar can detect and track aircraft and ballistic targets and provide fire control guidance for missile interception or artillery air defense. And this efficiently works in all weathers pretty well. So the apparent doubt will be how does a radar work if there are other echoes from land, sea, rain, snow etc. Hence, the next section is on factors affecting radar efficiency.
Source: https://www.bbc.com/news/world-middle-east-20385306
Source: Theodor A Postol via The NYT (The Indian Express)
Increasing Radar efficiency
The unwanted backscattered signals or echoes from insignificant objects like raindrops, land, sea, birds, etc., are generally called radar clutter. Due to clutter, detecting targets by the radar system in the environment becomes difficult. Hence, a significant part of radar design is devoted to minimising the effects of clutter without reducing the echoes from desired targets. The Doppler effect is usual in the case of moving objects; hence, echoes from the stationary objects can be differentiated easily. Now the question is, what about a raindrop also in motion. Here, we need to compare the object's size to a raindrop. Suppose we want to detect a missile or an aircraft with a relatively larger average cross-section than a raindrop. In that case, we can use a lower frequency wave in the microwave region (in a way, the wavelength should be larger than the raindrop). Because raindrops are more or less spherical (symmetrical) and aircraft are asymmetrical, circular polarisation can enhance aircraft detection in the rain. With circular polarisation, the electric field rotates at the radar frequency. Because of this, the electromagnetic energy reflected by the rain and the aircraft will be affected differently, making it easier to distinguish between the two. (In fair weather, most radars use linear polarisation; i.e., the direction of the electric field is fixed.)
Conclusion
So the discussion above is just the basic principle based on which Iron Dome works. Many technical details have been skipped. But the point is that such basic science principles joined with technologies can create wonders. The atomic bomb, used during a war, is a contribution of science. At the same time, science can provide safety systems like the Iron Dome to save lives. Hence, it depends on how we make use of science.
References
- https://www.britannica.com/technology/radar/Factors-affecting-radar-performance
- https://indianexpress.com/article/explained/explained-how-israels-iron-dome-intercepts-rockets-7312743/
- https://www.army-technology.com/projects/iron-dome/
- https://www.bbc.com/news/world-middle-east-20385306
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