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Modern Radar Performance for Drifting Obstacle Avoidance

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Alberto Fioretti
(@alby)
New Member
Joined: 5 years ago
Posts: 4
Topic starter  

Hi Ben,

Much has already been said about the new and enhanced features of solid state radars as aid to navigation (e.g. the Doppler assisted Target Analyzer of the Furuno DRS4D-NXT). 
Users report what I would call "fantastic" sightings of birds miles away from their boats  or even of floating tyres feet away from their bows. 
Unfortunately these reports do not qualify the context in which the sighting has taken place (i.e.  sea state, weather etc.) so they do not provide any reliable information on radar performance.
 
 My specific interest  stems from a plan that I have to cruise in the Arctic. Would these new radars perform better than my old magnetron radar at detecting ice growlers ?  (the NOAA defines growlers as: " small fragments of ice... extending less than three feet above the sea surface and occupying an area of about 215 square feet.")
 
I understand that you have been using the Furuno DRS4D-NXT for several years now.
Could you please comment on its capability to spot small drifting objects on the basis of your experience with it. ?
 
Thanks
 
Alby

   
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Jason Philbrook
(@jasonphilbrook)
Eminent Member
Joined: 6 years ago
Posts: 22
 

I think you should ask specifically for any first hand experience at detecting the growlers. Maybe Furuno has some contacts in geographic areas where that is likely.

From a general RF microwave background, ice has been pretty RF transparent though water is not.. Ice coatings on microwave dish radomes has not been a big issue, though slush and water affect signal greatly. I suspect ice will behave differently than most manmade objects in the water in terms of radar visibility.


   
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Ben Ellison
(@ben-ellison)
Estimable Member Admin
Joined: 6 years ago
Posts: 173
 

Hi Alby and sorry for the delay. My high regard for the Furuno DRS4D-NXT remains solid even now that I've had a little experience with all four current Doppler radomes --  https://panbo.com/navico-halo24-raymarine-quantum2-gizmo-goes-all-doppler-radar/ . In fact, I purchased the test unit from Furuno to be the boat's main (and testing reference) radar.

But I think that Jason just brought up an interesting point about ice and RF, and I have no personal experience with radar and growlers. The NXT does have good close range small target detection, especially in flatter sea conditions, and I suspect that the amazing automatic target acquisition -- very much like ARPA, though they don't call it that -- would work well with big ice, but I have not been in growler/berg situations.

At any rate, I will ask Furuno about it. Also have you considered a marine thermal camera? The cost has come way down since I wrote about this old schooner which appreciated their FLIR in the NW Passage:

https://panbo.com/nordwind-1939-gearing-up-for-the-northwest-passage/

Also, while probably not relevant to your situation, you may be interested in the FICE 100:

  https://www.furuno.com/en/merchant/iceradar/


   
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Alberto Fioretti
(@alby)
New Member
Joined: 5 years ago
Posts: 4
Topic starter  

Hi Ben,

             thanks a lot for your reply and thanks to Jason for mentioning the RF transparency of ice. Following his comment I browsed through the Internet and here is a relevant exerpt  from a  paper I have found ( https://lindzey.github.io/blog/2015/07/27/a-brief-introduction-to-ice-penetrating-radar/ ):

"...I've been working with ice-penetrating radar data for years, and I still think it's so flipping cool that we can see through kilometers of ice using radar. This is possible because ice is mostly transparent to electromagnetic energy at radar frequencies. We see reflections at the air/ice interface, within the ice where its properties change, and at the ice/rock (or ice/water) interface...".

Perhaps floating ice could appear on a radar screen because of the reflections at the air/ice and/or ice/water interface. Engineers at Furuno should have a pretty clear idea of whether that is possible as they have the experience gained in designing the rather extreme ice radar for the merchant navy. 

Thermal cameras would be good to have but a device in the same price range as the DRS4D-NXT would have to be a handheld device such as the Ocean Scout 240. Its specs promise that one would be able to see a small boat at night or in reduced visibility at about half a nautical mile, not bad at all if proven to be true. Fixed installation thermal cameras can perform better than that, but their price is several times that of the DRS4D-NXT  and they need more than twice the power. 

All in all, before thinking of a thermal camera (a portable one would be a very nice complement to radar) I feel that I should ascertain whether  the DRS4D-NXT can be of any use with ice. 

It goes without saying that if you could penetrate Furuno beyond the salesmen and reach the engineers that would be great indeed !

Cheers

 

 

 


   
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Alberto Fioretti
(@alby)
New Member
Joined: 5 years ago
Posts: 4
Topic starter  

Hi Ben,

            I come back again because I have come across a product  that reveals an interesting fact about radar performance with ice. This product can be applied to a  wider range of applications than simply detecting ice bits. In fact (according to its manufacturers) it can detect  a variety of small floating objects that could cause damage to hulls, rudders and props.   

The most interesting and revealing thing about it is that it is an add-on to any modern X-Band radar; stated in a different way it takes the output signal from the radar and uses digital signal processing (DSP) to extract the weak returns from small floating objects. This is very interesting in two respects:

1) It would seem to confirm that even if ice is essentially transparent at X-band frequencies, it probably produces weak returns from the ice-water and ice-air interfaces;

2) these returns are likely to go unnoticed on a standard radar screen but because they are nevertheless there, hidden in the noise, any modern X-band radar equipped with the advanced processing capability this product claims to have would show the small targets.

The specific product is very sophisticated, has lots of features and is clearly aimed at professional applications and possibly the very high end of the recreational crafts market. Yet it tells us that the limitations of a good recreational radar such as the DRS4D-NXT for what concerns detecting the presence of ice do not stem from any fundamental physical relationship between RF frequency and ice (i.e. its transparency) but rather derive from the limitations of its DSP capability.  For your info the link to the product is as follows:

https://rutter.ca/wp-content/themes/RutterWebsite/pdfs/sigmaS6SmallTargetSurveillanceSystemDescription.pd

In conclusion, if it is true that the DRS4D-NXT can detect birds then it can pick up weak returns and the question of it being capable of detecting ice and in what conditions remains an open question.

If you have access to the right person in Furuno then we could find out.

Cheers,

Alby


   
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Ben Stein
(@ben-stein)
Estimable Member Admin
Joined: 6 years ago
Posts: 158
 

Hi all,

I reached out to Furuno to understand their thoughts on detecting ice.  Below is what I got back from one of their guys who is consistently very knowledgable on their products and the practical applications of them.  He spent 8 years in the fishing business and quite a few years in Alaska, Washington, Oregon and in Russia.  He mentioned he spent some time in -55-60 degree air temps in the North Bering Sea, so definitely plenty of time around ice. 

 

A conventional radar high enough off the water – like an 800-foot Russian ship with the radar 125-150’ off the water – will see pack ice and polynyas (open areas of ice) just fine.  The more elevation above water, the better chance the radar has of both horizon and detection. But there are limits.

With regards to our Furuno DRS series radar of any generation, these radars would be capable of seeing ice when the ice presented a clear enough cross-section for conventional radar detection.  With that said – that doesn’t happen a lot of the time with “flat” ice, or ice that barely sticks out of the water. 

Furuno offers both ice and oil detection radars that operate differently than navigation radars, but actually use the same scanner info.  Navigation radars are built to eliminate clutter to enhance the image of “real” targets on the water – the stuff you don’t want to hit when you’re navigating (hence “navigation radar”). 

Our FICE (ice) and FOIL (oil) radar processors actually magnify clutter and use scan to scan correlation to composite images in order for vessel transiting ice to be able to tell where open channels are, whether they are naturally occurring or old tracks & trails from icebreakers.  This technology is similar in nature to the Rutter citation from your commenter, although of course we like to think we do it better….

It’s worth noting that both the US Coast Guard and Canadian Coast Guard use our FICE radars for ice navigation.

It’s easy to go down the ice-detection “rabbit hole” as it tends to devolve into a discussion of who can see bergs, “growler” ice, pack ice, shard ice, bergy bits, etc.  It’s like asking an Eskimo for how many types of snow there are, or an Oregonian how many kinds of rain there are. 

In short summary – all radars should be able to see ice if the ice appends above the surface significantly enough to present a detectable cross-section to the radar.  But just like the discussion of deadhead logs, submerged shipping containers and other stuff bobbing up and down in the water – if it doesn’t stick up consistently, it’s not going to be detected reliably on the radar screen.

Hope that helps some.  

He also provided the attached PDF of an August, 2018 article from Yachting on Furuno's FICE.  

Best,
Ben

Publisher, Panbo.com


   
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Alberto Fioretti
(@alby)
New Member
Joined: 5 years ago
Posts: 4
Topic starter  

Hi Ben,

           great !   Thanks a lot.  Your contact is clearly very knowledgeable and has given us a  very detailed and  informative account of what to expect  of a radar when dealing with ice.

Cheers,

Alberto

 


   
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