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Author Topic: AIS SART INFO from Jotron  (Read 18087 times)
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Glenn Dunstan
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« on: April 18, 2009, 13:27:44 »

Very interesting info from Jotron on their new AIS SART.



Innovative, is the correct word to use to describe Jotron AS and the
Company’s new AIS-SART.

From January 1st 2010, after several years of product development and standardization work
through international organizations, the AIS-SART will be adopted into the GMDSS regulations as
an alternative to the Radar-SART.

The unique and innovative feature of the AIS-SART is the combination of its physical size and
technical capability. The housing of the AIS-SART is identical to Jotron´s Radar-SART, type Tron
SART20, - that is a total height of 251 mm and a weight of only 450g.

Technically, the AIS-SART is based on the following principals; the unit will be programmed from
the manufacturer with a unique ID code and receives its position via an internal GPS antenna. This
data is combined and transmitted using the international AIS channels (AIS A and AIS B) in the
maritime VHF band.

How does it work?

The transmitter sends out a specified pattern. Every
minute, a sequence of 8 messages is transmitted, each
message is transmitted in a 26 ms time slot. 4 messages
are transmitted on channel A and 4 on channel B. All 8
messages are transmitted within a total time frame of
14 seconds. This time frame is defined to maximize the
probability that one of the transmissions hits a wave top.
It is only necessary to receive one of the 8 messages
from time to time to accurately locate the AIS-SART.


How do you know that this is an AIS-SART distress signal?
Anybody who can receive and detect an AIS signal will
also detect an AISSART.

The transmissionsignal from an AIS-SART
consists of an MMSI like ID code, where the first three digits
will be “970”. The ID code consists of a total of 9 digits and
the AIS-SART uses the remaining 6 digits to indicate a
manufacturer code (2 digits) in addition to the unit’s unique serial number (4 digits).

In addition to the ID code that appears on the AIS and connected equipment, an AIS-SART will also be visualized
on an electronic chart, connected to the AIS transponder onboard. An AIS-SART will be shown as a circle with a builtin
cross.

AIS-SART test results

As part of the process to define an international standard
for AIS-SART, 3 different tests have been conducted
by IEC / IALA. Jotron´s AIS-SART has been used as a test
object in all tests.

The initial test was done during the summer of 2008 in Oban, Scotland. The purpose of this test was to search for
the AIS-SART using a ship, and to determine the required output power of the unit. The results showed that it was
possible to detect a precise location from the AIS-SART at distances up to 8 – 10 Nm (Nautical Miles). Similar results
were obtained using the radar-SART, with the main difference being that the AIS-SART simplifies the search considerably
because the position is plotted directly on the vessels electronic map system, because the AIS is a fully digital
system. In addition, only one transmission of 26 ms is required to accurately get the position on the map, while the
radar-SART requires continuous updates.

The second test was performed in Oban in September 2008. This test was to determine the obtainable range from a
SAR helicopter. This test was done with a helicopter from the Maritime and Coastguard Agency (MCA), UK. Again, the
results were as expected and the signals were picked up at distances between 26 and 40 Nm at flights levels varying
from 300 up to 2500 feet.

The last test was performed outside Key West, Florida in January 2009. This test was performed by the US Coast
Guard (USCG), using a C-130 SAR (Search and Rescue) aircraft. The aircraft flew at different flight levels at 1000,
5000, 10000 and 20000 feet and recorded the maximum range that could be obtained. A search for a 406 EPIRB
and a radar-SART was performed at the same time to verify and compare the results that could be obtained with the
results from an AIS-SART. The AIS-SART´s were deployed at different heights above sea level to account for different
operating scenarios from a man over board unit to a SART mounted on top of a larger life-boat.

The ranges obtained ranged from 40 Nm up to 132 Nm from the AIS-SART mounted on a 1m pole.

These range tests, together with previous tests performed from both helicopters and ships, show that the AIS-SART
has a much superior performance compared with other locating transmitters (121.5, radar-SART). It can be located
at a far greater distance, with GPS precision, using standard equipment (AIS) that automatically positions the persons
in distress on a map. There is no doubt that the AIS-SART will contribute to a more effective and less time consuming
search and rescue operations in the future, with the result that more people in distress will be saved!

The interest in Jotron´s new AIS-SART has been overwhelming, both from the market and authorities all over the
world. Jotron expects to have a type approved AIS-SART during the summer of 2009. Furthermore, the AIS-SART will
be implemented in an appendix to the European Marine Equipment Directive (MED), probably in the summer of 2010.
In the meantime, authorities can issue national certificates to allow installation of the AIS-SART as soon as there are
type approved products available.

For more information, please contact Jan Erik Sæter, janerik.saeter@jotron.com
Jotron AS
April 2009

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Peter Leonard
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« Reply #1 on: April 21, 2009, 18:03:29 »

Hello Everybody,
 
Iro the AIS-SART, the test results look very encouraging and on that basis the equipment certainly will be of immense value to the GMDSS, however, an immediate comment is, why use an "MMSI like" ID instead of the vessel's actual MMSI? Using the "MMSI like" ID, to be able to identify the vessel with certainty one would have to be privy to the manufacturer's information iro serial numbers, etc, whereas using the actual MMSI, identification would prove so much easier. Disregarding the various sub-categories of info one may obtain from the MMSI format (such as whether or not it is a lifeboat, etc), in a real-life situation no deck officer is going to waste time looking up the format table to find out what the sub-category is! All he/she is really interested in is whether or not the transmission is from the vessel they are looking for. Provision is already made for MMSI numbers to be used on the VHF band in DSC units, so why not extend the use to AIS-SART's as well.
 
Perhaps I have missed something along the line,  Huh  if so I would appreciate being edificated. Shocked
 
Before I forget, thanks to Farokhi for circulating this on the old e-mail list. I have not yet got used to the new forum but will master the ins & outs eventually.
 
Cheers all
 
Peter

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Glenn Dunstan
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« Reply #2 on: April 22, 2009, 08:48:06 »

Good point, Peter.

Why not use the parent vessel's MMSI?

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Otto
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« Reply #3 on: May 01, 2009, 07:46:22 »

The reason for the special ID is:
The AIS messages is limited to an "ID" field of 9 digits, there is no extra bits for an extension to the ID. Because of this it would not have been possible to distinguish the AIS-SART from the main AIS onboard, or to distinguish various AIS-SARTs from each other if the ships MMSI was used. A ship may carry several AIS-SARTs that will be activated simultanously - it is neccessary for the AIS system that all these transmitters have different IDs - otherwise the AIS-SART symbol would have "bumped" around on the electronic chart according to the position of the AIS-SART that transmitted last.

Otto Holm / Jotron
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Glenn Dunstan
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« Reply #4 on: May 01, 2009, 09:45:57 »

Many thanks, Otto.

Welcome aboard.

Regards
Glenn
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