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RADAR

Nature of Target

Material of the target:

Different materials respond differently to radar pulses, in general all good conductors of electricity are in general good material for radar reflection.

Thus we have:

Surfaces that absorb and then re-radiate the energy on the same frequency – metal.

Surfaces that absorb and then re-radiate the energy on a different frequency

Surfaces which absorb and re-radiate very little energy, the balance energy is used to raise the temperature of the material – vegetation (microwave cooker)

Surfaces that are semi-transparent to radar energy – GRP/fibre glass boats

Thus we have steel, which is a very good reflector material, and wood that is a poor reflector material. As mentioned fibre glass hulls are extremely poor material for reflection.

Surface texture of the target:

Specular reflection, is a term used to describe reflection as would happen in an orderly way, the way a mirror/mirror like surface reflects light. Scattering is kept to a minimum.

Diffuse reflection is the opposite of specular reflection; here the reflection is not orderly since the roughness of the reflecting surface sends the reflected beam in a myriad of directions. Though the laws of physics are maintained the minute irregularities of the surface send the beam in different directions.

A perfectly smooth surface is smooth depending on the person feeling the surface. A child may feel a surface extremely rough which when felt by a workman’s hand would feel smooth.

The same occurs in nature, the smoothness of a surface is dependent on the wavelength of the light striking the surface and thus reflecting off the surface and entering our eyes.

Thus a surface, which has irregularities on the surface when a light beam is reflected from it, will appear to be smooth to a radar wave – which has a wavelength much longer than light waves.

So even though the light reflection would be diffuse from this rough surface, the radar beam would be specular.

This so because the wavelength of light is about 0.001 mm, in comparison to radar pulses which have a wave length of either 30 mm or 100 mm.

Thus a target the aspect of which is poor would if the surface were rough to radar waves appear to be a fairly good reflector.

Aspect of the target:

The aspect of the target is the angle, which the radar beam makes with the plane of the reflector.

Thus if the beam strikes the plane of the reflector at 90°, the aspect is said to be 90°. The reflection at an aspect of 90 will be the best and the reflection deteriotes as the aspect changes to any other angle.