Phase noise, coherency, and clutter suppression

Clutter is an unwanted radar return from nonmeteorological targets. Typically, these clutter targets are stationary, hard targets such as building, mountains, towers, etc. Other clutter returns, sea clutter, aircraft, birds, ships, and anomalous propagation are not from stationary products and thus are more difficult to characterize. Clutter suppression is a feature of modern weather radar. The clutter filter consists of a high pass filter, eliminating the returns with low radial velocity (ideally zero velocity) characteristic of stationary clutter. The clutter filter is typically specified as the type of filter (Finite Impulse Response, FIR, or Infinite Impulse Response, IIR), the delay inherent in the filter (number of poles or points), the rejection depth of the clutter (50 dB), and their width (0.05fPRF). Table I summarizes the filter specifications from a number of weather radar signal processors.