Rain Filter / FTC Control

[Brian - Raymarine]

Mr. Kelly,

The "Rain Control" in our radar products is actually an integration function working in the same way that FTC works, by clipping the leading edge of small signal returns to reduce the clutter caused by rain. However, do to the nature of X-band radar, rain is basically an impenetrable target, so attempts to "eliminate' it vary with the density of the precipitation (commercial vessels overcome this with S-band radars, whose wavelengths provide transparency to rain). While the sea clutter control can aid in reducing rain clutter, it operates in the time domain by attenuating rather than integrating; however, it will have some effectiveness to attenuate rain clutter depending on severity and range. I have, in general, found that our rain clutter algorithm works quite well under light rain conditions, but heavy squalls are a different challenge.