AIS RADAR - again!

[bedouin]

[ QUOTE ]

Both sustems require a level of operator skill in interpreting the data. As part of my job includes responsibility for running Merchant Navy Navigation Radar and Simulator Training I would suggest that the RYA 1 day Radar course is an absolute minimum for anyone who operates a leisure radar set, and this should be backed up with operating the set in clear weather to gain confidence in interpreting the display.


[/ QUOTE ]
Would you go as far as saying that a RADAR can be worse than useless or potentially dangerous with an untrained/inexperienced operator, or where undermanning means that insufficient attention can be paid to the display?

 

[srm]

First of all a caveat, I have not used the NASA AIS receiver, on the other hand I am familliar with both relative and true motion radar plots.

If the AIS receiver is giving true motion vectors (based on course and speed over the ground from the transmitter's GPS) risk of collision is not easy to spot. A ship on a collision course will usually have a vector that points away from your vessel (other than head on or overtaking situations).

In order to see if there is a risk of collision you also need to display the true vector for your own vessel to the same scale. Vectors are drawn for a specified time interval (I prefer 20 minutes but that is a choice). If two ships are on a collision course and will try to occupy the same spot in 20 minutes time their two vectors will touch at the end. If however the collision will occur in say 35 minutes the two vectors will not touch, but point towards each other, you would have to extend the time of the vectors to confirm risk of collision or a crossing situation.

If own ship remains in the centre of the screen on the AIS display and you plot the other ship's apparent track on the screen a vessel on a collision course will appear to follow a line towards the centre. This is because own ship remaining in the centre of the screen is a relative motion display.

The comments above assumes both vessels are experiencing the same tide or current. If they are in different streams you have no way of simply predicting risk of collision with vectors or relative plots. It also assumes that both vessels will maintain course and speed as this is a prediction based on past performance.

Hope this helps, diagrams would have made the explanation easier.

Sean

 

[srm]

QUOTE
"Would you go as far as saying that a RADAR can be worse than useless or potentially dangerous with an untrained/inexperienced operator, or where undermanning means that insufficient attention can be paid to the display? "

Good question, but not useless if used with care. The first time I tried steering a vessel at night by radar the skipper had to interveen before I ran it aground. There was a lot of publicity about a yacht that was run down a year or so back while crossing the channel due to misinterpretation of its radar display.

On the other hand practice in daylight and good visibility relating the display to the real world soon builds up experience.

If navigating by radar in poor vis the navigator needs to pay full attention to the screen, you can not glance at it occasionally and expect to interpret it. On unstabilised ships head up (small boat radar) My technique is to put an ebl on a target and see if the target runs down it towards me at the centre. If it does, there is a serious risk of close quarters or collision.

Sorry must go, could write more.

Sean.

 

[jonjo]

[ QUOTE ]
Only if all vessels are experiencing an identical current rate & direction

[/ QUOTE ]
I do not know what the debate is about any more. Vectors generated from RADAR or AIS will be unreliable if one vessel is going to experience a change in tidal set as the vessels close.

Having read your reply and reread your original post a few times I now think you are criticizing the presentation of information on the NASA screen and not doubting that collisions can be predicted from AIS broadcasts.

Is it possible that NASA rotate the target tails to account for the predicted course of the host vessel?

 

[crossbones]

You have not fully understood the user instructions.
The trails left by ships on nasas ais radar are relative to the users position. It is accurate to say that,if neither party change velocity,then a collision will ocur if a ship "points" towards the user. These trails do not erase on changing range.
The unit also provides absolute data available from the targets gps. It is a clever bit of kit.
The "tracks" you mention is an entirely different feature on the unit where time lapse pictures can be built up. By the very nature of this facility it would make no sense to change range in the middle of a run.
On this site I feel people should not make adverse comments on products they haven't tried.

 

[roger]

Re: AIS live availability limited

The aislive.com site displays an increasing number of sea areas with the commercial ship traffic on them - but not for long. The service goes subscription only on about May 3rd. If you want to have a look I suggest you register now. They say they plan to have a free service with 1 hour delay after that date.
I find it fascinating if not very useful to see traffic entering Kobe port in Japan for example.

 

[Oldhand]

I'm getting very bored with this, I strongly suggest all who are not or have not been very regular users of radar read at least chapters 3 & 5 of "Radar Navigation and Maneuvering Board Manual" which can be downloaded at:

http://pollux.nss.nima.mil/pubs/pubs_j_show_sections.html?dpath=RNM&ptid=10&rid=244

When that has been fully absorbed, everyone will be in a much better situation to discuss NASA's AIS "Radar" as a stand alone collision avoidance tool and to better understand how to use radar. For those who think because I haven't used this particular piece of equipment I am not fit to comment on it, I have been studying live AIS plots with trails, prediction vectors and instant updating for some 2 months and can't see why the NASA equipment should improve on what I have been watching.

 

[ClassicPlastic]

Well, it seems to me that Robin was spot on! Francis, consider yourself 'radar' identified!

We now need to optimise our web-radars to identify the target name under which this spin-meister will reappear!

Using radar itself is difficult enough - using a 'radar' that only sees some traffic - and then, God forbid, attempting to correlate a sighted target with the AIS target at night in a busy shipping lane - is a recipe for disaster.

I've done some more thinking, and have concluded that this might be a useful add-on to a primary radar, in order to identify particular vessels, and corrrelate RTF-derived knowledge, for example (You've heard 'BIG SHIP' saying that they're dropping anchor, you see a target in the anchorage, and then identify it as BIG SHIP by AIS).

BUT... I wouldn't wish to be on a boat on which this kit was being used, other than in this manner.

 

[Graham_Wright]

Have you told Nasa this?
Their advertisement still refers to transponders.

 

[Graham_Wright]

The AIS principles are well described here;-www.gpc.se/aisusa/uscgais.htm.

Fascinating that they use the words "broadcast" and "transponder" in the same sentence!

 

[jonjo]

[ QUOTE ]
the NASA AIS will not calculate collision vectors but merely displays your track as determined by your COG ...

[/ QUOTE ]
Since my first reply to you others have raised additional points about the NASA product, I now think it is computing collision vectors internally but this information is simplified in the display by twiddling the target tails.

 

[francis39]

[ QUOTE ]
Well, it seems to me that Robin was spot on! Francis, consider yourself 'radar' identified!


[/ QUOTE ] Its a fair cop, Guv! I have to confess to having some connection with NASA! I met them last year when my wife and I were visiting the White Cliffs National Trust site. NASA were there testing their prototype AIS radar. I had a very long chat with them. As a retired radar engineer (mostly airborne, millimetric FMCW, not marine, I’m afraid.) I found we had much in common. Much of my understanding of AIS came from that long (to my wife’s exasperation!) chat, supplemented by later researches on the Web.

I have no boat, but I have a friend who has. He advises (and I’m sure you’ve all heard this before) that it’s like standing under a cold shower, washing £50 notes down the drain as fast as he can go. Accordingly, he doesn’t recommend me getting a boat now I’m retired. He has got an AIS radar, though, following my glowing reports of the White Cliffs chat with NASA, and he asked me to respond to some of the dotty stuff being put onto this forum - I’m beginning to wish I’d kept my counsel. I’m no navigator, either, and I have resisted (wisely, it seems) responding to some of the other daft threads, such as the one about diesel fuel’s “life”, as only one example.

If anyone wonders whether contributors have manufacturers’ allegiances, I think they should consider whether those who most vitriolically condemn NASA’s radar might be disappointed competitors who are trying to damage NASA, either out of envy or simple irritation that they didn’t think of the idea first. I hope NASA do well with this one, because they seem to be a successful all-British company, and as such, as taxpayers, are helping to pay my old age pension! I shall in future keep quiet.

 

[BrendanS]

I for one have no connection with NASA or any other marine company. I still think Nasa's choice of the word Radar for this product is extremely bad and ill advised marketing, and hope they dump it (the term Radar at least)before it hopelessly confuses more people.