Raymarine C Series Reference Manual page 137

Chapter 6: Using the Radar 123
Rain or snow clutter
The radar can see echoes from rain or snow. Returns from storm areas and rain squalls
consist of countless small echoes that continuously change size, intensity and position.
These returns sometimes appear as large hazy areas, depending on the intensity of the
rainfall or snow in the storm cell.
Interference
When two or more radar-equipped vessels are operating within range of each other
mutual radar interference can occur. This usually appears as a spiral of small dots from
the display centre This type of interference is most noticeable at long ranges.