AIS "radar" information please

Re: AIS \"radar\" information please

Whilst the product is still relatively new then sensible owners will realise that it isn't a RADAR in the terms that they understand.
We have already had queries and misunderstandings about how the AIS DISPLAY works on here.

It will not take long for ppl (and likely to be the newer ones to the game) to forget that it the Leisure AIS Display/Engine is a receiver only and will look at the name of the product for a quick description - and potentially believe it is more capable than it is. A system is normally only really tested when used in anger - which is not the time to realise that it doesn't do as expected.
 
Re: AIS \"radar\" information please

Sorry, but you miss the point. SSR transmissions are linked to the primary radar - in fact using a colocated antenna which rotates with the primary dish, sending out interrogation signals which return the ID and flight level at the same time that the primary is painting the target range and bearing

In other words, SSR is part of the radar equipment and merely enhances the target detail. Which is why it's called SSR

AIS works on a completely different principle. The only thing they have in common is that both can fail or be switched off.

So can my (radar) bilge pump!
 
Re: AIS \"radar\" information please

What are you going to actually say to the ship(s) when you call them? Let me start the call off.......

"Big Ship, Big Ship, this is Little Yacht, Little Yacht calling on Ch16 (or the DSC equivalent of all that)". "Little Yacht, this is Big Ship, go ahead, over" ...they select a working frequency then..."Little Yacht this is Big Ship, how can I help, over?" "Big Ship,.......". What are you going to say at this stage? If they are a collision risk, haven't you already sorted that out? If they are not a collision risk and you don't need urgent assistance, what are you going to talk about?

This suggested use of AIS - i.e. being able to call ships via DSC - always puzzles me. Why would I ever WANT to call a big ship? What would I ask them to do? Alter course for me?
 
Re: AIS \"radar\" information please

Hi John,[ QUOTE ]
Understand the question but question the relativity. Does anyone really care what it is called - .....

[/ QUOTE ] While I have views about the uses (and abuses) of the AIS system used in yachts, I am asking a semantic question. "Who in the world is responsible for defining the term "radar""? Can I call a pair of binoculars with compass a 'radar'; after all, light is an em wave and I can estimate range! Can I call a dog a cat? To whom do we defer on these matters - the IMO, the RYA, Raymarine or the Battersea Dogs' Home? Whether or not AIS is a good bit of kit does not come into it, I am simply asking who has the 'right' to decide that one thing is a radar and another thing isn't? Ofcom have a view as they include it in the licence details but do they define 'radar'? And do they have the 'right' to define it? Maybe it doesn't matter much to anyone, but I matters to me - you can't have anarchy in a language when it is used for technical things.

David
 
Re: AIS \"radar\" information please

I understand how Secondary and Primary Radar operate. I worked for two years on a radar control and monitoring sytem for the CAA in the early 80s.

My point is that both SSR and AIS are secondary in that they rely on the monitored station transmitting data to the monitoring station - how that transmission is triggered and how the recieving station paints the target is a separate issue. AIS does the painting based on the data transmitted (GPS position), SSR paints on the basis of the synchronised primary radar signal bouncing back. Both use RAdio and signal Detection to to achieve this And both use Ranging - calculated from the received signal - so both are RAdio Detecting And Ranging - RADAR.

I can't imagine that you bilge pump uses radio waves or signal processing for its operation so it definitely isn't RADAR.

Ed
 
Re: AIS \"radar\" information please

An interesting torture of the acronym RADAR

Radar uses measured radio bearings and ranges, not calculated (unless you want to count the primitive speed of light)

AIS simply receives messages which include positions etc from which ranges are subsequently calculated

Radar detects all reflecting objects. AIS detects only the ships which have it fitted and switched on

SSR only replies to the interrogating primary radar base. AIS broadcasts to all

I can only hope you weren't working at the sharp end of the CAA
 
Re: AIS \"radar\" information please

EdEssery is completely wrong and Tome is maybe a little bit wrong (unless I misunderstand him and looking at his last post I think I do in that Tome is referring to the ground station Tx as "primary"). I have worked alot with both primary and secondary radars for both civilian and military use around the world (although not for a few years).

SSR indeed depends on interrogation of the transponder but position in azumith and distance are determined (in a complex way) by the TX interrogation to response propagation time and the shape of the SSR's antenna pattern. Primary radar does not come into it, SSR depends on the interrogation transmission and can (and often does) operate without a co-located primary radar.

The transponder includes identity, flight level, etc (Mode S can provide GPS position as well) but that is the only bit that is similar to AIS but even in that SSR is still quite different in that AIS transmits all the time (usually) and determines its own transmission slot, whereas a SSR transponder only transmits when interrogated and position (except flight level) is determined by propagation similarly to primary RADAR in all except both the aircraft and the ground station provide the propagating rf and the reflection is active instead of passive.

For aviation the surveillence method that is equivalent to AIS is Automatic Dependent Surveillance-Broadcast (ADS-B) where the aircraft continuously tx position, speed , identity, altitude, etc which is only just being implemented - it is NOT being called RADAR by anyone (perhaps cos there is no one in those circles silly enuff to call it RADAR).

SSR is properly called RADAR. If it is to be correct that AIS is also properly called a RADAR then anything that continually announces its position, identity, etc in its own time slot MUST also be called a RADAR - which would be silly cos then if I sailed along continually announcing my position speed, etc on VHF then I too could be called Radar (but as he is actually a character in MASH it would be a doubly stupid thing to call me).

I'm sure that won't end the argument as some will never be convinced /forums/images/graemlins/crazy.gif.

John
 
Re: AIS \"radar\" information please

Bloody hell John, I was trying to keep it simple though I take your point about co-location not being necessary for SSR

You also know very well that Mode S is military only so doesn't come into this

My bilge pump is an inductive load, and when it switches on it radiates nasty RF briefly so I still cannot see why I shouldn't call it RADAR
 
Re: AIS \"radar\" information please

you really must not get into an argument about electronic matters with tome. you will be wrong and you will end up on the receiving end of some personal abuse /forums/images/graemlins/smile.gif /forums/images/graemlins/ooo.gif
 
Re: AIS \"radar\" information please

Baffle them with science I say /forums/images/graemlins/smile.gif.

Mode S is approved by ICAO for civilian use and as far as I know is being implemented (I think Eurocontrol are supposed to have both elementary and enhanced surveillance Mode S operational sometime next year) - but Mode S civilian is after my time /forums/images/graemlins/smile.gif.

Also, I may not have been clear, SSR does not need a primary radar at all to work and is entirely independant of primary radar (primary radars are usually in higher air traffic density areas only). Not sure if that is what you meant or not, but probably was and add only to avoid confusion as I was not entirely clear on that.

Is your "radar" a Rule one by any chance or some other make?

John
 
Re: AIS \"radar\" information please

So are we agreed that AIS is an information system and not a radar? /forums/images/graemlins/smile.gif
 
Re: AIS \"radar\" information please

could you imagine the confusion if ships AIS's became transponders - interegated by each receiver??!
 
Re: AIS \"radar\" information please

It could easily be done but it would take a huge amount of extra bandwidth and the equipment would be far more complicated and expensive. It would also be pointless and do nothing that the passive receivers already do.
 
Re: AIS \"radar\" information please

Within the UK Flight Information Region, Mode S has been required for all aircraft flying IFR within specified Mode S airspace since March last year. There's a 2 year transition period to allow everyone to catch up though.

Is it (or AIS) radar? Who knows? Who cares? I know what it does. I know its limitations. It works.

Angus, the Jellycopter pilot. Wobbling a speciality.
 
Re: AIS \"radar\" information please

John,

Thanks for that. I was trying to keep it relatively simple. My point is that dissing AIS because Nasa have chosen to give it the title "Radar" is semantically an incorrect thing to do.

It is quite a while since I worked in this area. I was interested to read what you say about ADS-B and googled it, coming up with this link from the FAA which says:

"As an simplified example, consider an air-traffic control secondary radar. The radar measures the range and bearing of an aircraft. The bearing is measured by the position of the rotating radar antenna when it receives a reply to its interrogation from the aircraft, and the range by the time it takes for the radar to receive the reply. The beam of the antenna gets wider as the aircraft get farther from the antenna, thus making the measured position information less accurate. An ADS-B based system, on the other hand, would listen for position reports broadcast by the aircraft. These position reports are based on accurate navigation systems, such as satellite navigation systems (e.g. GPS). The accuracy of the system is now determined by the accuracy of the navigation system, not measurement errors. The accuracy is unaffected by the range to the aircraft. With the radar, detecting aircraft velocity changes requires tracking the received data. Changes can only be detected over a period of several position updates. With ADS-B, velocity changes are broadcast almost instantaneously as part of the State Vector report. These improvements in surveillance accuracy can be used to support a wide variety of applications and increase airport and airspace capacity while also improving safety."

From this we can infer that ADS-B is an advance on SSR. SSR is an advance on Primary radar but does not replace it, although as you infer it is used as the the main source of data for Air Traffic Controllers (backed up by Primary). I guess ADS-B will take over from SSR in due course.

Similarly I expect AIS will become more prevalent than Radar in the leisure boating industry. It has a lower cost of entry, a lower demand on watchkeeping time and the above statements on ADS-B advantages apply to AIS equally. Some people will continue to use Radar either as the primary detection mechanism or in addition to AIS. Each to his own....

Personally I'm going with GPS and AIS.

Ed
 
Re: AIS \"radar\" information please

Thanks for that Jellycopterman /forums/images/graemlins/smile.gif.

Your post prompted me to look at the NATS internet site to see if I could find more on that but the site seems to be just full of fine words with nothing at all that I could find describing plans, developments, existing facilities and systems, etc /forums/images/graemlins/frown.gif.

John
 
Re: AIS \"radar\" information please

Noone has been "dissing" AIS - well I don't think they have - there is just concern over the chosen name - AIS Radar ... as the general view from the users on the forum is that it is misleading to include the term RADAR in the name as it implies the unit does more than just receive, process and display data. That said - I believe general consensus is that AIS receivers are an excellent compliment to Radar and are useful for non-radar users - so long as the limitations of AIS are understood.

The major disadvantage to AIS is that the receiver is entirely passive and waits to receive signals from transmitters - it has no way of confirming that information - where as trad RADAR, as you know, is active - and is only reliant on reflections of a signal it sent.

There are plenty of leisure boaters who still do NOT realise that vital difference and may get a shock in poor vis when a non-AIS transmitting vessel is seen too late.
 
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