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Module 1.4: How does RADAR work

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How does RADAR work?

Radar works by transmitting an electromagnetic signal and then waiting for reflections from that transmission to be received. The Radar will accurately measure the ‘time delay’ between sending the transmission and receiving the reflection. As the speed of light is constant in air (and electromagnetic waves travel at the speed of light) the Radar can accurately calculate the range (distance) between it and any object causing a reflection.

Simple example

In the simplified example below, you will see a Radar mounted on a ship. This would transmit a signal which travels away from the ship equally in all directions simultaneously until encountering two ‘targets’, one is a land mass (represented by a cliff face) and the second is another vessel (represented by a fishing boat).

In both cases, some of the energy is reflected back. The reflected energy travels back to the ship where it is collected by the Radar and displayed as a response on a screen.

The display is simply a graph of amplitude (size) of the received signal against time delay; the signal is represented by the green line. This type of display is known as an A-Scan, or Amplitude Scan.

By chance, this example shows both targets at equal distances from the ship resulting in the reflections having the same arrival time, this is why only one response is shown.

How does RADAR work?

Radar works by transmitting an electromagnetic signal and then waiting for reflections from that transmission to be received. The Radar will accurately measure the ‘time delay’ between sending the transmission and receiving the reflection. As the speed of light is constant in air (and electromagnetic waves travel at the speed of light) the Radar can accurately calculate the range (distance) between it and any object causing a reflection.

Simple example

In the simplified example below, you will see a Radar mounted on a ship. This would transmit a signal which travels away from the ship equally in all directions simultaneously until encountering two ‘targets’, one is a land mass (represented by a cliff face) and the second is another vessel (represented by a fishing boat).

In both cases, some of the energy is reflected back. The reflected energy travels back to the ship where it is collected by the Radar and displayed as a response on a screen.

The display is simply a graph of amplitude (size) of the received signal against time delay; the signal is represented by the green line. This type of display is known as an A-Scan, or Amplitude Scan.

By chance, this example shows both targets at equal distances from the ship resulting in the reflections having the same arrival time, this is why only one response is shown.

The Radar in this example has identified an object at a given range, but it is unable to determine exactly where the object is or differentiate between the two different targets. That makes this Radar limited as a useful application.

Note: this is a highly simplified example and does not accurately represent how Radar works in real world situations.

Heading: Making Radar useful

What would be required in this example is a modification to the Radar so it could provide the missing information (in this situation it would be to differentiate between the two separate targets and determine where they are with respect to the Radar). It is possible to do that by narrowing the beam, and then moving the antenna so that the Radar transmits in different directions individually.

This allows it to look in a particular direction to see if there is anything there: if yes, how far away is it? And then move to the next position. This information is represented on a PPI or ‘Plan Position Indicator’.

The PPI is a circular display which positions the Radar in the centre and the targets represented as responses with a direction (angle in degrees) and a range (in meters or kilometres).

The Radar would now be considered useful as we have overcome the two primary disadvantages from the first example by making some simple changes to the design. It can now be used to detect and range objects.

Note: Again, this is a simplified example and not exactly representative of real life, but it gives a good idea how a radar works.

The Radar is not able to identify targets but it is able provide some information about them from their size. Low lying land (for example) might look very different to the cliffs.

To start looking at how a basic knowledge of radar introduces and relates to the concepts of Ground Penetrating Radar (GPR), please visit KB GPR Training Module 2.1: Introduction to GPR.

Our Most Common Questions

Frequently Asked Questions

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What can a Ground Penetrating Radar survey detect?

With GPR, you can detect a wide range of objects below ground level, including both metallic and non-metallic objects such as plastic pipework. GPR will also identify and map any voids below the surface, such as air pockets or mine shafts, as well as any other irregularities including concrete and previously excavated or back-filled areas.

Will GPR compromise safety on my site?

GPR equipment emits an electromagnetic pulse into the ground and records the reflected signals from subsurface structures and voids. It is entirely non-destructive and will not break the ground’s surface or affect any objects below. What’s more, it doesn’t emit any harmful levels of radiation, nor are there any other by-products created throughout the process. This means it’s entirely safe to use by its operators, and on sites of any type, including those open to the public.

Is a GPR survey 100% accurate?

While GPR is one of the most effective methods of non-destructive testing available, it can never be 100% accurate. One factor that can adversely affect the accuracy levels include the type of soil being surveyed. Clay soils and soils that contain high levels of salt or minerals can obstruct the GPR reading. Another factor is the experience of the equipment’s operator: interpreting the data collected can be complex, which is why it’s beneficial to commission surveys from an expert firm.

Is GPR equipment difficult to use?

The equipment itself is not difficult to use, but the interpretation of the data recorded tends to be complicated. The results of a GPR survey aren’t automatically translated into an easy-to-understand picture of what lies below the surface; instead, it’s a series of lines and waves and it can take both training and years of practice to master the art of correctly reading the output. Often, it is the experience of the equipment’s operator that plays the most significant role in the accuracy of the results GPR can achieve.

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