AIS through satellites.

[GILow]

Yep, I won’t argue. Ballast Head royally sucks right now. Still stuck here with wind, rain and monster waves between us and home. Delayed by five days now.

[JPA Cate]

Maybe quarantining due to Covid19?

[wholybee]

Class B AIS has less power, and is much less reliable for Satellite reception. Also, the complete AIS transmission with all the details happens much less frequently with Class B (maybe 6 minutes I don't remember) than just the position and MMSI. So it is likely that when a Satellite receives a signal from a Class B, it will not know all the details, and have to be given as an unknown vessel.

[GILow]

Originally Posted by wholybee

Class B AIS has less power, and is much less reliable for Satellite reception. Also, the complete AIS transmission with all the details happens much less frequently with Class B (maybe 6 minutes I don't remember) than just the position and MMSI. So it is likely that when a Satellite receives a signal from a Class B, it will not know all the details, and have to be given as an unknown vessel.

Yes, you are right about the power and frequency bit, however the unknown vessel bit is about whether or not you choose to pay Marine Traffic for their satellite data service.

In my case I am more concerned with.why my satellite cover is so poor. I am still not sure if it is a product of my AIS system, my antenna placement or my geographical location.

[GILow]

Originally Posted by JPA Cate

Maybe quarantining due to Covid19?

Happy to say it is not an issue here in South Australia. I was a little worried about how the island locals would respond to us but I didn't need to be.

[sy_gilana]

Hi, let me chime in here a bit.
Those sats were not designed to do AIS, but one day, a techie was fiddling with the software controlled radios on board the birds, and found a string of data at the frequencies used by ais. He got the strings decoded, and reported it to Management, who saw some $$$ on an underutilized radio and a new business was born. All MRCC's get this info for free.



Class B Sometimes gets through. Class A usually gets through.

Now to antennas. go to this page

Quadrifilar helicoidal antenna - Javascript on-line calculator
and work on 162 Mhz


This will get your signal up there and to ships. The radiation diagram will almost be spherical.

[StuM]

Originally Posted by sy_gilana

Hi, let me chime in here a bit.
Those sats were not designed to do AIS, but one day, a techie was fiddling with the software controlled radios on board the birds, and found a string of data at the frequencies used by ais. He got the strings decoded, and reported it to Management, who saw some $$$ on an underutilized radio and a new business was born.

Where did you get that idea from?

https://ro.uow.edu.au/cgi/viewconten...text=lawpapers
2. SATELLITE AIS. In 2003, at the fourth International Academy ofAstronautics (IAA) Symposium on Small Satellites for Earth Observation, a paper from the Norewegian Defence Research Establishment, Forsvarets Forsknlnginstitutt(FFI), was presented that focused on new possible roles of small satellites in maritime surveillance (Wahl and Høye, 2003a, 2003b). The authors presented the possibility of using a space-based AIS receiver to assist in vessel tracking by providing timely reports with vessel identification and additional information. The paper noted that developments in micro-satellite technology could pave the way for these satellites to carry passive sensors for ship detection, including Synthetic Aperture Radar (SAR)imagery and reception of AIS messages from ships.

The Norwegian Defence Research Establishment et al developed the concept for monitoring Norwegian waters and launched the first AIS satellite (AISSat-1) in 2010.

Subsequently a number of companies have spent a great deal of money launching constellations of dedicated SAIS satellites.

All MRCC's get this info for free.

I think that you will find that governments pay for the data from those commercial entities and use it for many different purposes. The government may provide it to the MRCCs "for free", but it's not provided for free by the satellite operators.

[El Pinguino]

Originally Posted by sy_gilana

.....

Class B Sometimes gets through. Class A usually gets through.
.......

I would beg to differ.... and suggest the majority of Class B transmissions are received by satellites...

Some years ago I took a 14 day trial subscription with marinetraffic.. it was very educational and worth doing...
Its a bit tricky as you have to give your c/c details and if you forget to cancel before the fortnight is up you are hit with a full 12 month charge...

Way to go is to sign up for the trial and then cancel straight away... you still get the 14 days...

Anyway... all the Class B pleasure craft ( you have to make the not too bold assumption that the vast majority of pleasure craft are operating class B - this is checkable after signing up for the trial) that were coming up 'unknown' then come up with all their details.

Go to an area where you have a fair idea of the amount of traffic to be expected... in my case the eastern South Pacific.... filter (the icon top left in the pic below) for pleasure craft and click your way through them..

Reduced numbers on the move just now due to Covid and the season for americas to FP passages being just about done..

However.... look below... vvv

[GILow]

Meanwhile, it appears our neighbour, Caspian Harmony, set sail this morning. And a quick look at Marine Traffic suggests a number of boats had delayed their transit of the Great Australian Bight for the weather. Either that or they’ve taken up badly organised line dancing...

[El Pinguino]

Another interesting ( or maybe not ) thing... ships can show up twice... look over at Leeuwin and you have an 18 hour old terrestial position for Tantabiddi (Class B ).. you can also see her down the track a bit with an 28 minute old position near Walpole.. I bet she shows up again off Albany....

[GILow]

Originally Posted by El Pinguino

Another interesting ( or maybe not ) thing... ships can show up twice... look over at Leeuwin and you have an 18 hour old terrestial position for Tantabiddi (Class B ).. you can also see her down the track a bit with an 28 minute old position near Walpole.. I bet she shows up again off Albany....

Ummmm... are you still on the free trial of satellite data? Because I only see a generic unknown yacht off Walpole.

Either way, that’s an impressive trip in a 5 meter boat!

[El Pinguino]

Esp a 5 metre boat with a 3 metre beam... I suspect finger trouble...

I can still see a last terrestrial position 19hxxm ago off Leeuwin ( about 34º58', 115º11' ).

I think ships 'drop off the plot' when no new info is received trestrally for 24 hours...

My 14 day freebie expired long time ago....

[GILow]

Originally Posted by El Pinguino

Esp a 5 metre boat with a 3 metre beam... I suspect finger trouble...

I can still see a last terrestrial position 19hxxm ago off Leeuwin ( about 34º58', 115º11' ).

I think ships 'drop off the plot' when no new info is received trestrally for 24 hours...

My 14 day freebie expired long time ago....

So... just to be clear, you see an unidentified sailing boat south of Walpole? Right?

And yeah, 15 meters x 3 meters is more likely.

Which reminds me... I’ve been meaning to let zenith_adelaide know his AIS data is a little odd for a monohull. Particularly as Mr O’Kelf designed relatively slim boats..

[El Pinguino]

State of confusion = situation normal...

Yes, I am assuming the unidentified one is Tantabiddi... low traffic area.... only two AIS PVs around...

[GILow]

Originally Posted by El Pinguino

State of confusion = situation normal...

Yes, I am assuming the unidentified one is Tantabiddi... low traffic area.... only two AIS PVs around...

That’s two more than the Gulf St Vincent at the moment. Which means everyone else was smarter than us.

Going to try and make a run for it tonight, around midnight. Fingers crossed we will reappear on AIS, but it will end my satellite cover experiment.