NASA AIS - is it a RADAR?

[francis39]

There have been lots of comments about whether it is or isn't a "real" radar. Some have argued it can't be because they have found lots of dictonary references which suggest (amongst other things):

Definition: [n] measuring instrument in which the echo of a pulse of microwave radiation is used to detect and locate distant objects...

Radio waves are sent out and reflected back from an object...

A method of detecting distant objects and determining their position, velocity, or other characteristics by analysis of very high frequency radio waves reflected from their surfaces...

device for finding range and direction by ultrahigh frequency point-to-point radio waves which reflect back to their source and reveal position and nature of objects sought.

The reason they all think that NASA's AIS radar is not real is because they see the words "echo", "reflected", "microwave", "very high frequency", "ultra-high", etc. If those were really essential pre-requisites of a RADAR, then the pre-war Chain Home Radar systems would be disqualified (too low frequency).

The word RADAR, despite the assertions of the dictionaries they quoted, is far wider than that narrow interpretation. I have referred to the radar "Bible" - the Radar Handbook by M.I. Skolnik, amongst others.

For example, I find that there are plenty of passive radars that don't transmit at all (try Googling "passive radar"). There are plenty of radars that do not transmit pulses (Google "FM Continuous-Wave" or "FMCW radar").

Surely no-one asserts that the radar guns (!) the Police use aren't radars because they don't provide direction or range information. I doubt whether magistrates would accept it as a valid defence!

The Secondary Surveillance radars used by air traffic controllers very closely resemble in function the operation of the AIS system, which free-runs (as do SSRs when they "squitter" - look that up, too!).

So, on balance, I think the choice by NASA of the word RADAR for their AIS unit is fair. And they did need to distinguish it from the sister unit - their AIS Engine - which has no display at all. So shouldn't we be discussing the latter's lack of pistons?

 

[Robin]

You can call it what you like as long as people understand that it doesn't give the same information by a long way as does what is known as a conventional Radar set. That it only shows vessels that are fitted with AIS transmitters.

It will not show:-

Land
Buoys
Leisure vessels of any size
Fishing vessels
Coasters less than 300 tons

Someone else said about this if it quacks like a duck it is a duck. Well this one is more like an ostrich head in sand about to be hit in the a**e by a fishing boat.

Useful addition to but no replacement for radar in the conventional sense, USE WITH CARE!

All IMHO of course /forums/images/graemlins/smile.gif

 

[Anonymous]

It doesn't really matter what the origins of a word are - are you going to reclaim 'gay' to have as its primary meaning 'happy or jolly'? What really matters is what the word means to (educated) people today. To all mariners, marine radar is an apparatus that transmits pulses on designated frequencies and, from the return 'echo', deduces the range and azimuth of the 'target'. An 'AIS radar' would imply a radar that also has the capabilities of AIS. These are available, but not at a price that most yachties would afford - yet.

So, if the forthcoming NASA offering is an 'AIS radar' then what shall we call a 'genuine' radar that also displays AIS? An 'AIS radar radar'?

 

[jonjo]

Re: RADAR everywhere

Great so I already have multiple radar devices on my boat.

When I pick up a torch and scan around for a buoy nearby I am sending out a beam of EMF energy and can receive the reflected response on my eyeballs.

A better analogy with AIS would be my navigation lights. They send out continuous information about the orientation of my boat using the EMF spectrum. Any eyeballs in the area can then interpret where my boat is heading.

 

[Talbot]

The analogy with IFF is very fair, as that is exactly what AIS is - a secondary system originally designed to back up real radar with additional data. The designation SSR stands for Secondary surveillance radar. Thus it would be more appropriate to call the NASA system - AIS SSR.

I am much more concerned with the problem alluded to in one of the earlier posts, that people will buy this sytem thinking that they were getting a radar and SSR system. As it is, I consider the designation to be deliberatly misleading, and after 30+ years in the marine radar business I would have no hesitation in stating this in front of an appropriate authority. I really recommend that you re-think this designation.

 

[Ships_Cat]

I agree with the strong possibility of confusion in the pleasure market.

I am not quite so sure it warrants in any way the term radar through comparison with SSR, however. In the case of SSR the ground station interrogates a transponder on the aircraft and both the transmitted and recieved signals are used for azimuth and distance fixing. As has has been said transponders in Mode S transmit unsolicited information ("squitter") but essentially position fixing still depends on interrogation from the ground "radar".

AIS does not work like that (limiting ourselves to the ship to ship case). The ship station just transmits and is also never interrogated by another ship. It may come to pass that in the future such interrogation may take place between ships as it may now in the shore to ship case, but as I understand it the subject equipment does not do that.

If AIS is to be called a "radar" then, for example, if you make a voice transmission of your position on VHF and plot it on something (or even maybe not do that) then you to deserve the title of "Radar" (like in the film MASH, I assume /forums/images/graemlins/smile.gif).

In fact, simple position requests using VHF DSC are much more deserving of being called "radar" than AIS is, but I doubt whether it will come to pass that DSC VHF's will ever be called such.

Given the low sophistication of many pleasure users as far as the terminology is concerned it seems even more troublesome to call any AIS a radar, it will surely lead to confusion.

John

 

[Talbot]

I used the analogy with SSR because of the supplement to data, rather than a strict comparison of techniques, but then you could hardly compare Mode 1 IFF with Mode 4. From a functionality viewpoint, the comparison is correct. I was trying to remove any question of technique cause 99% of readers will not be interested, and 0.5% proabably already understand, which leaves 0.5% unsattisfied /forums/images/graemlins/smile.gif

 

[Anonymous]

[ QUOTE ]
Given the low sophistication of many pleasure users as far as the terminology is concerned it seems even more troublesome to call any AIS a radar, it will surely lead to confusion

[/ QUOTE ]I propose "AIS Polar display", or "Polar AIS". Actually, in due course, radars will be mostly cartesian. All LCD radars could as easily be cartesian as polar even today.

 

[Ships_Cat]

Hi Mark

No, I wasn't trying to be picky with your post. Frank made the direct comparison with SSR, especially with respect to "squitter".

As you say, many will not know about SSR (and IFF), but perhaps seeing the claimed comparison challenged they may see that the claim is challengable (if that makes sense - erk /forums/images/graemlins/frown.gif)

John

 

[ShipsWoofy]

This is said without trying to upset any posters or insult anyone contemplating buying the NASA AIS RADAR.

Isn't this dumbing down a bit petty? Arguing over whether it is an IFF (Information Friend or Foe) or in fact RADAR, passive RADAR or none of the above. For all it matters NASA could call the unit AIS magic box.

Do people really believe anyone is going to buy this unit as a replacement to a RADAR? No one is going to part with the best part of £250 without asking questions or completing some research into the product first.

This is quite a specialist bit of kit, those who desire will already know what AIS is and will have a use for such a system. To suggest a normal bod will walk into a chandlers and see the word radar and hurriedly buy one and fit it and then be upset as they realise it is not a primary RADAR.

Give people a little more credit, this is a great system on paper and will be of great use to those frequenting busy shipping areas, but those that do that will already be aware of the dangers with respect to playing chicken with ships.

We cannot in life reduce everything to the lowest common denominator, the system is another piece of information to a skippers arsenal, if the skipper is really that confused by the information available from this set, then maybe, it is more dangerous to have it fitted than not. But I suggest those who will fit them, will be quite intelligent enough to use it safely. Those who have never heard of AIS will either pick it from here, see it in action a friends boat or never require one as sometimes ignorance it bliss.

People have been traversing busy shipping areas for years without anything but a compass and cup of coffee.

Please give the masses some credit.

End of Rant

 

[Anonymous]

[ QUOTE ]
Do people really believe anyone is going to buy this unit as a replacement to a RADAR? No one is going to part with the best part of £250 without asking questions or completing some research into the product first....Give people a little more credit, ....We cannot in life reduce everything to the lowest common denominator.......Please give the masses some credit

[/ QUOTE ]I can't speak for anyone else but it had never crossed my mind that anyone fit to take a vessel to sea would be confused about the capability of their gear. This is a new class of equipment and unless a proper name can be ageed for it it will make life difficult for us when we read books, articles, sales information or are just talking to other friends/yachtsmen. The whole point about language is to be able to communicate. If the term 'radar' is used to mean 'a style of display' rather than the fundamental apparatus then the term 'radar' will become useless without qualification. 'AIS radar', 'AIS radar radar', and what will we call proper radar? 'Traditional radar'?

No, my objections have nothing to do with safety or people who are foolish enough to purchase a product without research, my objection is that NASA are taking an important and common term and making the word practically useless unless it is further qualified. We ought to tell 'em that though the product sounds good, they will have to come up with a better name. I wonder why they should want to call it 'radar' when it clearly isn't? Is it like the old margarine vs butter war?

 

[Talbot]

[quoteI can't speak for anyone else but it had never crossed my mind that anyone fit to take a vessel to sea would be confused about the capability of their gear.

[/ QUOTE ]
I was not concerned about the vast majority of people who as you rightlly say are fit to take their vessel to sea. My worry is purely about that small number of people who are manifestly totally incompetent, but still buy boats and then put RNLI lives at risk.
As to definition of competency, surely if you are REALLY competent with the use of a radar, there is actually no need at all for a piece of kit like AIS. I have certainly managed for more years than i care to relate, without thinking that I needed anything extra.

 

[Ships_Cat]

I don't know what it is like in the UK but I have come to wonder how much looking and understanding some do when buying.

I do some marine litigation stuff from time to time. It never fails to impress me how seemingly many people buy whole second hand boats (not just the bits on them like radars) which are piles of junk and then only work that out after they have had them for a year or so - then they look for someone to sue so it does not look like their fault that their boat is now scrap.

Have even been involved with some cases where the aggreived ones bought second hand boats that were piles of junk and it turned out that they had not even looked at the boat nor had any pre-purchase survey before handing the cash over /forums/images/graemlins/crazy.gif.

So when it comes to AIS, radar, etc I can imagine more than a few not having a clue as to the differences.

John

 

[Birdseye]

Ships cat is correct - just sold my boat to someone who bought without survey. As it happens its a good boat so he should be OK.

Given the large number of people who have claimed that they didnt understand the pension they were sold (and pensions are pretty simple things) I have no doubt that people will buy the Nasa product thinking it is a full radar and not being willing to make the small mental effort to understand how it works and what it does. This forum has a fair number of people who dont understand simple basic technical matters.

To my mind its the punters problem. But some Trading Standards guy is likely to take the issue up, get himself some publicity etc.

 

[Robin]

I don't usually disagree with big black dogs but I have to say I have talked to people (and seen posts on the forums) that quite plainly do misunderstand what AIS can, or more importantly cannot, do.

Notably:-

I have heard people say that AIS sets send out information to other sets. True BUT leisure sets are receive only so your info is NOT available to others, they cannot see you any better because you have an AIS receiver on board.

I have heard several people liken it to the Air Traffic Control System - Wrong, not everything out there is transmitting data and there is no transponder to be interrogated. You only get data IF it is sent and IF the vessel has the equipment and IF they decide (for security or other reasons) not to switch it off.

I have heard people say they are only worried about big ships, everything else is likely to be slower and easier to miss. Good luck, that is really Ostrich mentality!

IMO if you are worried enough to want to buy something to help, buy RADAR (the proper one), even if secondhand (same price as AIS?) if it is power consumption that is the concern, run the engine with the RADAR on. Then consider AIS as an addition to not a replacement for proper radar.

With sincere apologies to all out there (Woofy especially included) who are grannies that know how to suck eggs!

 

[Strathglass]

NO


It is a Complex RDF set.
It is much like an old RDF radio but instead of picking up individual low frequency radio signals with a morse identity it picks up transmitted signals from individual ships with their unique identity and presents them in a in a radar type format on the NASA display.

There is a limitations of this type of set.

Unless there is a transmission from the obstruction then as far as the NASA device is concerned it does not exist.

In other words it will not detect - rocks, the shore or vessels with no transmitters fitted (small craft?) or switched off (faulty)

I imagine it is still a very usefull device but unlike a radar set it does not generate it's own signal and will only display and quantify signals transmitted by other vessels.

Iain

 

[paulsmith]

If you look on the AISlive.com website it gives ship positions at various ports around the Uk and around the world, however coverage is limited to areas around the approaches to ie Milford Haven including the inner Harbour but does not appear to cover the Bristol Channel Approaches Say around Lundy Where I sail. Does this mean the NASA kit would also not work in the areas not covered on the IAS website?

 

[Piers]

AIS transmits a ship's info on a VHF frequecy. If you are within receiving distance, your AIS receiver will detect the information.

AISlive depends upon land receivers in the areas shown on their websites, and is therefore limited to those areas. But that's only for their website, and does not effect what you receive.

 

[Thistle]

No! AISlive relies on link-ups with port AIS installations ... and only some ports have paid the 2500 Euros to link their systems. NASA - and other - AIS receivers should work anywhere but rely on there being AIS transmitters within range.

Remember that AIS - like GPS, sextants, compasses, charts and eyeballs - are simply aids to navigation. They provide inormation which may be inaccurate or incomplete. The skipper must decide what information to rely on and then make (and be responsible for) all navigational decisions for their vessel.

 

[fireball]

What would be the effective range of AIS receiving once out in - for example - the channel? VHF is (theoretically) line of sight - so say 30Nm range (big boat antennas are higher than ours) so if mid way in the channel should be able to receive boats from both coasts and have a few minutes warning on those in the seperation zone?.... if they are transmitting ...