When a radar beam is emitted from a source/transmitter, it impacts the objects in the line of sight of the beam. The objects reflect signals back, that are captured by the radar's receiver, which trace/map the various objects including moving targets (MTI). The return signals are from radar are known as returns. The return signals are comprised of returns from aircraft, ships, ground, etc. The return signals that are not wanted by the radar are classified as noise and clutter. The clutter is specific to the type of radar. The signals from atmosphere are useful signals to a weather radar, signals from moving objects are useful for defence/military activities and so on.

Types of Clutters

Surface Clutter: Return signals from ground/land and sea are known as surface clutter.

Volume Clutter: Return signals from weather and chaff are known as volume clutter.

Point Clutter: Return signals from tall buildings, birds and insects are point clutter.

References

[1] Signal to Noise Ratio

[2] Radar Tutorial

[3] Aerospace and Defence