Radar system works on the echoes received from the target in the range of RADAR. In real world these targets are determined in the presence of noise other than the receiver noise. RADARs have to deal with more than receiver noise when detecting targets since they can also receive echoes from the natural environment such as land, sea and weather. These echoes are called clutter. Clutters may also originate from multipath echoes from the valid targets due to reflections from ground and atmospheric ducting.

Basic types of clutter are:

1. Surface clutter: Echoes from the sea or land are surface clutter. Echoes from land masses are stationary and from the sea has movement and causes Doppler shift so can be removed using signal processing techniques.
2. Volume clutter: Echoes from weather and chaff are volume clutter. In the air volume clutter is produced due to rain or snow.
3. Point clutter: Birds, tall buildings and windmills are point clutter. Birds and insects produce clutter which may be very difficult to remove because the characteristics are much like aircraft.

Properties of the Surface clutter can be defined by grazing angle of radar such as low, medium and high angles.

For low angle the maximum echoes come from spatially localized or discrete vertical features associated with the high regions of the visible landscape such as tree, building, fences etc.

When sea clutter is considered, nature of echoes from sea depends upon the shape of the sea surface. Echoes are obtained from those parts of the sea whose scale sizes (roughness) are comparable in dimension to the radar wavelength.