AIS Marine Tracking Bight path openings

[VK2KRR]

VK5AKK Phil up to around 1900 km this morning with numerous spots and one south of Perth.

VK5AKK 11.12.12

[VK2KRR]

A very nice past 24 hour map from Phil VK5AKK.

VK5AKK past 24 hr map 11.12.12

[VK2KRR]

Also nice 24 hr map from VK5ZEA, some spots north east of Perth and good spread across the Bight.

VK5ZEA 24 hr map 11.12.12

[9A4CU]

Great coverage ! What sort of antenna has he got in Port Lincoln?

[VK5AKK]

I believe Michael's AIS Rx is using a folded dipole through a cavity filter at the crowded repeater site of VK5REX.
Not sure of the altitude of Winter Hill, around 250m ASL with great views over Port Lincoln and surrounds.
Rex VK7MO had success from this spot working 843km to VK3 on 10 gig SSB.
Cheers
Phil

[VK2KRR]

I think this thread is probably right for this mornings opening from Phil VK5AKK atop the Adelaide hills, who did get right across the Bight, but not only did his marine tracking station hear signals near Perth, but also right up to the oceans of the north west corner of VK6, out to approx 3300 km.

So without getting further into it at this stage, here are the maps and stats from this morning, will post more info shortly -

VK5AKK past 3 hour map

VK5AKK past 24 hour map

VK5AKK stats page

[VK2KRR]

While I would usually suggest that such paths as what it appears that Phil has discovered, are NOT possible, due to the nature of the deep inland areas that this signal path would have taken to get from the northern most spots; I cant fault anything with this and it appears to be legitimate (not a software or web error). So now looking further into all possible data sources for weather conditions etc.

Looks like there is no access the the University of Wyoming upper air sounds page any longer, so at this point I cant run the data through the AREPS program. Ive requested the raw data through BoM though.

Looking at other info for this morning, the Hepburn charts do show some interesting, unstable propagation areas moving well inland into VK6. While not fully along all these path areas at once, the fact that there is 'colour' showing up on the map inland in VK6 is quite unusual in itself. The Hepburn charts are a guide/prediction only.

I think this first one is 1800 utc on Boxing day morning, but the older prediction. But with this I wanted to show that approx 50% of VK6 inland is covered in some coloured area, albeit with unstable marking around them -

Older Hepb 1800utc boxing day

The latter 1800 utc boxing day map, still with extensive unstable areas across VK6 -

Hepb 1800 boxing day

BoM 5am MSLP map -
A possibility the low pressure trough having something to do with it (and the unstable condx)

5am MSLP map

[VK2KRR]

Next up some satellite cloud images.

Notice where the cloud line is on these, and ive drawn approximate signal path area on them also -
Firstly 5am -

5am Satellite

Also 10am to show the cloud retracted back north -

10am Satellite

Have seen signals skirting below cloud mass before in these situations. In the boxing day duct 2003, and also duct 02.01.06 when I had a path to VK6JR. Cloud & MSLP shown here -

Cloud 02.01.06

I'd say this is all the data I will be able to find on the opening unless the BoM have some vertical radiosonde data.

[VK2KRR]

Last night about 11pm Phil Vk5AKK's marine tracking station showing spots right out to 2950 km west Brilliant.

VK5AKK 28.12.12 pm

This morning 29.12.12 early AM, I had 3 vessels at Esperance WA @ 2298 km, and also numerous spots in the waters west of Adelaide.

VK2KRR 29.12.12 am

[VK6ADF]

Just adding a little bit of info to what Leigh has been posting. At 2305 on 26/12/2012 VK5RAC-1 APRS digipeater was gated by VK6MF-5 in Manjimup.

[VK3HZ]

As a possible explanation for Phil's results, the AIS network includes Repeater stations. I have no idea of their locations, but perhaps there is one around Perth that was relaying the reports from the ships up the west coast? No doubt Phil had good propagation to the west (he worked 3 VK6's) but perhaps his AIS Rx was only directly hearing across the Bight to about Perth.

[VK5AKK]

Greetings David,
I have never heard of an AIS repeater. After all the system was designed for ships on the high seas to see each other locally, so no repeaters neaded.
There are however stations with multiple remote receivers feeding back info from a remote site and uploading it with their home data.
For example if a station had their home Rx and another Rx 500km away at a busy harbour, their stats would show a minimum Rx distance of around 500Km, never anything less.
As an example have a look at station 396. He must have at least six remote receivers feeding back to his station.
I have one antenna, one receiver and upload my data to one site.
Hope this helps.
Cheers
Phil

[VK3HZ]

Hi Phil,

Forgive me but I'm a perpetual skeptic. I'm wanting to believe that you had coverage all the way up the west coast, but it's a difficult thing to explain unless an Es cloud conveniently drifted northwards.

The reason I mention repeaters is that they are described in Wikipedia. Google found this (among many): http://www.alltekmarine.com/products_de ... d=6&gid=16

Also, there's an AMSA site in Fremantle that lists both Rx and Tx capabilities: http://web.acma.gov.au/pls/radcom/assig ... ID=2224270

I'll do a bit more digging when I get the time.

Regards,
Dave.

[VK2KRR]

Hi Dave, Phil,

I am not aware of any RF repeater stations in the AIS system around Australia at all. There are however a number of maritime safety base stations. These base stations usually TX information in regards to virtual aids to navigation. The safety base near Drysdale on the SW side of Port Phillip Bay, I pick up regularly here. It transmits the required data for the aids to navigation so they show on the ship displays and they can then navigate safely.

I doubt there would be a repeater station around Perth, as there is not any receive stations located there in any case to hear the signal, there is only 1 at Fremantle and then VK6APK and VK6ADF north and south. Note there are no ships visible in the Swan River up near Perth. Im sure of the the stations mentioned here could answer the question if there is such a station there.

For Phil to have these spots logged with the marine tracking server against his station number, he would have to have been the station that got them to the server first, no other station can log them once the first reaches the server. I would think that the delay of a signal having to go into and back out of a repeater would delay the reception enough to where others would have the signals logged who heard them directly.

If you were to compare to say VK6APK there were numerous signals being heard from north - south. As you see with Phils (5AKK) map he only has around 20 spots logged in scattered area up the coast.

I must admit I was real skeptical at first also, but to me it appears that the low pressure trough that sometimes assists VK6APK to hear signals up to near Christmas Island is what may have assisted Phils reception. The trough was quite a way inland and the sothern end appeared to have shifted to a SE direction and then follow back up north. This possibly linked up to the existing tropo already in the Bight. Thus giving Phil similar access to the more northern areas, similar to what VK6APK would hear near Bunbury.

Better data could be had if Phil had shipplotter set up as he would see all of the data he heard saved to his computer, not just what is logged with the server.
Phil has heard signals north of Perth before, just not this far north. But this is the one and only time this has happened so far north.

I tend to believe it happened. If it happens again we can then gain more data to compare it with to work out how/why. Phil hears signals near Perth reasonably often in these openings so we'll wait and see.

[VK3HZ]

Hi Leigh,

You're probably right. However, when looking for anomalous propagation with ADS-B, I've spotted aircraft a number of times that weren't in the "right" place, including a 767 which "landed" 1km to the east of the Melbourne Airport runway! So sometimes the position reports are not what they at first seem (the skeptic, again ).

According to the Wikipedia AIS description, "... With the help of repeater stations, the coverage for both ship and VTS stations can be improved considerably. ..."
So, it seems repeaters are used to enhance ship-to-ship propagation in areas where there may be obstructions - say when rounding a headland.
The transmission protocol is packetised, so it seems the repeaters use store-and-forward. No idea if the receiving station would notice any difference from a direct signal.

And from the AMS submission to the ACMA on the five-year spectrum outlook: "... Currently, AMSA has 35 licensed AIS base stations/repeaters in operation around the Australian coast, and has 5 more pending applications. In addition, there are currently some 25 non-AMSA base stations/repeaters/receivers ...". So they are around. It may be that the repeat function is not explicitly identified on the map because, for the users for which AIS was designed, it's not of any relevance.

Regards,
Dave.

[VK6ADF]

Hi Leigh,

I've spotted aircraft a number of times that weren't in the "right" place, including a 767 which "landed" 1km to the east of the Melbourne Airport runway! So sometimes the position reports are not what they at first seem (the skeptic, again ).

Yes the position reports sometimes do need to be taken with the proverbial grain of salt. I have seen a Oil Tanker being shown in Mt Isa (the ship variety not a road variety). With shipping it would be easy with such short transmissions to maybe miss a bit and display the wrong location, for one ship but I would doubt for many at the same time. I sometimes wonder if it is pings from a meteor being received when just one or two loggings are recorded. If it occurs over a period of time with several reports being received I am happy enough to say it's a proper detection in my own mind.

A few lighthouses around here issue AIS signals. I am guessing that they might be some of those base stations/repeaters/receivers mentioned.
AMSA Aircraft also have AIS fitted so that takes care of at least 6 licenses. Maybe the rescue boats also would come from that pool of licenses as well so that takes care of a few more, perhaps.

Sending the data direct from your PC to Marine Traffic you don't really know what is being received till it finally gets processed and displayed on their webpage and if the logging has already been detected by another then I don't think it shows up on your stats map immediately anyhow. Using other software you get to actually see on screen what is being received, from where, live, and then that software sends the data to Marine Traffic.

[9A4CU]

I do not think that repeaters are improving pictures of AIS reception .If you check daily reception of particular station you can see during poor condition how far station can get data from ship.If repeaters play game here,why we can not see improvments in coverage during poor condition?
I would like to mention VK6APK just because he is the only one from VK6 who send feed to Fleetmon.com
When condition are good his antenna is receiving all the way almost to Cocos isl. but in poor propagation his reception is around Bunbury or maybe bit of Fremantle or south.Where about is repeater to improve picture of reception? I do not think they installed repeaters 20 meters ASL!Repeater coverage should be much better during poor conditions but it does not show it.
Anyway, if someone else would like to improve AIS picture of VK6 or any other area and send feed to Fleetmon just add this
remote IP 193.189.247.193 port 33000 . At least they have better chart than MT,reckon!

This is reception of VK6APK.

[VK2KRR]

Dave,

Yes, you may also be right yourself, its hard to say. I'll try find out some more info if such a repeater station may exist today if I get a chance.

I know there are repeater stations available designed for AIS, I just have not heard of their operation in Australia.
As Phil VK5AKK mentioned, im not sure why they would need to extend AIS coverage where ships use the service for collision avoidance. Because 162 MHz will get over most/all nearby structures, some of the ships required to use the service are HUGE, their antenna heights would have to be at least 60ft above the water in some cases (cargo ships/tankers) and usually hear at least 20 km under normal conditions.

I can only think a repeater would be used to extend coverage to an RX station with poor or no coverage of the the coastline ?

[VK2KRR]

I have just found out the story on Phil's big 3300 km reception. Unfortunately it appears it didn't actually happen via direct radio path.
I'll give u all the run down on it shortly.

[VK2KRR]

This afternoon I got in contact by telephone with Mark, the person who runs the Fremantle AIS station.

I explained to him what had happened, that Phil had seemed to have logged some spots right up the NW corner of WA over 3000 km. Virtually straight away he said "yep, that was my fault sorry".

I asked him what the story was and he explained that what happened was that he hooked up an older marine tracking receiver that he used in a previous location a while back. This just happened to still have the old port numbers in it that he was allocated a few years ago, which now just so happen to be the same port numbers as what Phil VK5AKK was issued with for his station 146.

Realising that nothing was being logged to his own station, he realised that they were being sent to he older original port, now allocated to Phil, and so he changed his port sending destination and its running as per normal.

So, what he is saying is that there is no repeater station, Phil did not receive these spot RF signals in any way shape or form. But what happened was when the Fremantle station began hearing further north west that morning the data received at the Fremantle station was actually logged to Phils port number accidently and then fixed a short time later.

So there you have it, a simple explanation really.

This does highlight the importance of running your data into the Shipplotter program (or similar) directly on your computer before its sent to the marine traffic server. With Shipplotter you see and log everything that is heard to your computer hard drive. I know Phil (and others) dont want to have to run a computer all the time, but if Phil was running Shipplotter, these spots up the coast would not have shown up on Shipplotter and only been seen on MArine traffic maps, and we would know instantly that something was not right.

In any case we are all learning more and more every day and this is just part of the learning curve.