Messages on AIS

[joha]

Good evening all.

Have just been reading the users manual for the Vesper Watchmate 850 and it has a bit about recieving messages ie weather. Does this work in the UK or across the channel?

Reghards

J

 

[RobbieW]

I think this refers to a Binary Message option available to 'competent authorities' allowing either addressed or broadcast messages over AIS. I havent read of this being implemented in Europe for broadcast type messages like weather. It apparently has been implemented in the St Lawrence Seaway for lock heights etc.

That messages can be sent using AIS surprised the hell out me. Going along minding my own business when the plotter squeaked, it was a specific message - a little confusing as the name on the stern had been changed but the transponder not updated, eventually worked out it was intended for me

 

[prv]

I think this refers to a Binary Message option available to 'competent authorities' allowing either addressed or broadcast messages over AIS.

If you read up on the AIS protocol (yeah, just what we all do for fun ) there's all kinds of weird and wonderful capabilities designed in that I don't think are actually used.

Pete

 

[AngusMcDoon]

More AIS dullness than you'd imagine possible right here...

http://gpsd.berlios.de/AIVDM.txt

 

[RobbieW]

Some other, more readable, stuff here. This appears to be a 2008 paper that, with a bit of further searching, starts to show some implementations around the UK coast - one of which is connected with the London Olympic site, again to do with lock water heights.

 

[VicMallows]

Fascinating. Thanks for bringing it to our attention. Does sound strangely reminiscent of SMS on mobile phones .... which was originally thought to be an insignificant background service which had no real commercial potential.

 

[Amphitrite]

Hi,

AIS has the capability to transmit both text messages (free SMS-like text with AIS Class A and restricted, pre-defined content for AIS Class B for leisure craft) and binary messages which follow a certain content table. Some message are used on the St. Lawrence (weather, water level, lock information) and in inland AIS, for example Austria on the Danube.
However, there is also a set of weather messages and afaik some buoys of the Irish coast in the Irish sea transmit them, as well as stations all around Sweden. They contain synoptic information regarding with direction, speed, gusts, wave height, water temp etc, if all sensors are connected.

Holger

 

[joha]

Thanks guys. Suprised the hell out of me too, as I had never heard of this before and could be quite useful.

J

 

[testmonkey]

looking at AIS log files from last week's sail I see these entries, what do they mean?

$PSRT,SBAS,02,03*2B
$PSRT,SER,,,3D36*33
$PSRT,ALM,01*44
$PSRT,GER,02*57
$PSRT,SBAS,02,03*2B
$PSRT,STXT,00,MAYDAY MAYDAY *22

Was someone in distress? Nothing like that heard over VHF...

 

[RobbieW]

Closest match I could find was from this blog. Looks like its a proprietary ($P), and unpublished, protocol (SRT) which carries information from a common AIS component to whatever devices are attached to the AIS board via NMEA. Presumably if the devices dont recognise the protocol header they discard the message but its still there in the log.

 

[ianj99]

With ever more static locations such as light houses and light buoys being fitted with AIS transmitters, it strikes me that AIS is being set up to act as a sort of backup for the GPS network if it is ever disabled or partially disabled due to satellites being knocked out by solar flares / mass ejections...

Obviously its only a 'better than nothing' option for use within range of land rather than any serious substitute for GPS or proper chart work.

There's probably a lot of untapped potential in the system.

 

[yesod]

With ever more static locations such as light houses and light buoys being fitted with AIS transmitters, it strikes me that AIS is being set up to act as a sort of backup for the GPS network if it is ever disabled or partially disabled due to satellites being knocked out by solar flares / mass ejections...

i'm not sure that ais will work without gps, given it relies on the gps system to co-ordinate transmissions slots (sotdma).

 

[RobbieW]

Virtual buoyage

Another idea I came across whilst looking at some of this stuff is that of virtual buoyage. An AIS location that doesnt physically exist, initially perhaps as a quick response to an obstruction. Long term you could see the attraction of buoyage that required no physical onsite maintenance

 

[ianj99]

Another idea I came across whilst looking at some of this stuff is that of virtual buoyage. An AIS location that doesnt physically exist, initially perhaps as a quick response to an obstruction. Long term you could see the attraction of buoyage that required no physical onsite maintenance

True for moving objects, but not for the static ones I mentioned, so you can use them to establish a fix, assuming several were in range.

What would be the point in outfitting these unmanned locations with AIS gear otherwise?

 

[yesod]

True for moving objects, but not for the static ones I mentioned, so you can use them to establish a fix, assuming several were in range.

how on earth do you think ais works????

 

[RobbieW]

True for moving objects, but not for the static ones I mentioned, so you can use them to establish a fix, assuming several were in range.

What would be the point in outfitting these unmanned locations with AIS gear otherwise?

I may be being slow today, but about the only reasons I can think of to fit the gear to fixed locations are:
i) its cheaper because an off the shelf transponder may be used

or
ii) they are in locations without good VHF coverage from other land stations.

For virtual bouyage it would be possible to have an AIS transmission with fixed position and MMSI data that could be broadcast from anywhere within range of the position you wanted to mark.

 

[ianj99]

how on earth do you think ais works????

You've missed my point.

I am aware that gps is needed for moving objects but I see no reason why a static object cannot have a means of retaining it's (unchanging) location in memory and therefore can continue to transmit this when the gps signal is lost. ...

As far as I know, all gps units retain their last known position if the signal is lost...

Try marinetraffic.com to see which static transponders are listed. (They are also used as part of the VTS)

 

[yesod]

I am aware that gps is needed for moving objects but I see no reason why a static object cannot have a means of retaining it's (unchanging) location in memory and therefore can continue to transmit this when the gps signal is lost. ...

yes, i understand that. the point i can't understand is how you propose to

....use them to establish a fix, assuming several were in range.

 

[testmonkey]

You've missed my point.

I am aware that gps is needed for moving objects but I see no reason why a static object cannot have a means of retaining it's (unchanging) location in memory and therefore can continue to transmit this when the gps signal is lost. ...

As far as I know, all gps units retain their last known position if the signal is lost...

Try marinetraffic.com to see which static transponders are listed. (They are also used as part of the VTS)

AIS transponders need GPS as UTC timing source for the SOTDMA (Self Organized Time Division Multiple Access) protocol to avoid collision of transmissions...

 

[ianj99]

Oh well not such a good idea after all, though I did think it possible using the same basic principle as employed in tracking mobile phone locations using the cellular network.