JRC JMA-5212-4/6 User Manual page 326

[III] Coping with sea clutter and rain and snow clutter
When the weather is bad and the ocean is rough, the use of an S band radar is effective because the radar is
not influenced by sea clutter so much and attenuation due to rain drops is small. When an X band radar is
used, reducing the pulse width will reduce the influence by spurious waves, and also the spurious wave
rejection function effectively works; therefore, the use of short pulse is effective when the weather is bad.
By using image processing functions PROCl 1 to 3, it is expected that spurious waves are further
suppressed. Since optimal settings for those items can be automatically made by using the function mode,
it is recommended that STORM or RAIN be used by selecting the function mode when the weather is bad.
For details of the function mode, see Section 3.10 "USE FUNCTION SWITCH [FUNC]".
However, these functions may make some targets invisible, particularly targets with higher speeds.
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