Rain Filter / FTC Control

[Ian Kelly]

We are using a 48" Super HD array with e127/125 series MFDs. We are finding the Rain filter ineffective other than possibly a small effect on the inner 1/3 of the screen around the boat, and there does not seem to be an FTC control. We are typically operating in Harbour preset mode with a range of .75 to 3.0 miles and have found the only way to paint a useful picture in rain/snow is to manually reduce the gain, with the related risk of loosing targets. In the e-series MFD manual there is reference to an FTC control for the non-HD digital radomes but not the HD or Super HD radomes or open arrays. Is there a way to penetrate rain showers in the outer 1/3 of the screen, as an FTC control would do, without reducing gain?
Thanks,
Ian

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum Ian,

How is the performance of the system when operating in the absence of precipitation. Is this a ground station application or one in which the equipment is installed onboard a vessel. Should the equipment be installed onboard a vessel, are the symptoms reported associated a vessel is tied to a dock or positioned within relatively close proximity to hard objects which would produce strong returns (i.e. buildings, ships, etc.)?

[Ian Kelly]

The performance is excellent when there is no precip. We normally operate in harbor preset with auto gain and have seen no need for manual gain except in precip. The unit is mounted on a marine SAR vessel about 8ft above the water. The symptoms occur within 0.5 to 3NM of shore and in open water, and become less of an issue in narrower channels when we are ranged in.

Thanks

Ian

[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.

[Ian Kelly]

Interesting - it sounds like our radar is probably operating normally and manual gain reduction may be the best option when the "Rain Control" is ineffective. Am I reading this correctly? Thanks for your advice on this.
Ian

[Brian - Raymarine]

That would be a true statement depending on the radar cross section of targets you would like to view. Rain clutter is most effective at shorter ranges (i.e. < 1.5nm) as the RCS of hard targets will provide greater signal strength.

[Brian - Raymarine]

Image of effectiveness of rain clutter control - dual radar setup: