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What’s that Ship? or AIS for Landlubbers by Stan Swan What is that ship sailing past? Where’s it heading? When is it due in port? What is its speed? How big is it? For all these questions – and many more – the answer is AIS: Automatic Identification System. You may even follow it, on line, on your own computer – from anywhere! 12  Silicon Chip siliconchip.com.au R eaders may recall a few months ago we featured a means of identifying aircraft and following their progress using a hardware and web product called AirNav Radar Box (SILICON CHIP, November 2008). Now you can do much the same thing with virtually all commercial shipping and even many of the larger pleasure craft you see off our coasts. Somewhat akin to AirNav Radar Box, you have the choice of tracking in real time (using a VHF receiver or scanner) if you live close enough to the coast or alternatively, using the internet where details of that ship may well have been posted. But we are getting slightly ahead of ourselves! Ship watching Even viewed from the shore, ships often conjure up an exotic sense of far away places and tap an eternal human wanderlust. Many a ship-watcher has idly gazed at passing vessels and pondered their destination and movements – particularly if one’s vantage point is from a becalmed yacht in a busy sea lane! Both at a romantic and utilitarian level, even a casual interest in shipping movements from a coastal location near sea lanes could mean an emerging VHF wireless technology called AIS – Automatic Identification System – may take your fancy. Essentially a SOLAS (Safety of Life At Sea) collision avoidance system designed for professional seafarers, AIS shows immense potential even for landlubbers! It’s a fascinating blend of software, radio, electronics and enavigation, yet can be experienced on skinflint budgets. Interested? But it sounds like digital sea-sickness? Gain your AIS sea legs instead (and to whet your appetite!) go to www.marinetraffic.com/ais/! Just select a busy region (perhaps the Straits of Gibraltar) from the global map and zoom in to suit. Mouse-hovering over a coloured display symbol gives vessel details, while a right mouse click shows ship images and near-live vessel tracks. The versatile real-time insights gained from this are quite astounding and should enthuse even hesitant landlubbers! Keeping track . . . of a sailing ship with AIS. The Spirit of New Zealand off the northeast coast of NZ. You can even see how the ship is tacking from the southeast before it makes its due-westerly run into Kawau Island. There’s even a photo of the Spirit under canvas so you can see what she looks like! Collision avoidance “Full speed astern!” Over past centuries of powered shipping, no doubt siliconchip.com.au The Channel is getting pretty crowded! This is just a tiny section with AIS showing cargo vessels, passenger vessels, tankers, ships under way, ships moored . . . August 2009  13 Commercial AIS equipment – at right the text-only SIMRAD A170, photographed on the bridge of the Norwegian coastal vessel MF Bastø II by Ulf Larsen. (Courtesy Wikipedia). Below is a Smart Radio SR161 AIS Receiver, an entry-leve single channel scanning receiver designed for both recreational and professional use. (Courtesy Milltech Marine). this urgent command has been the last request handled by many engine-room telegraphs! Radar (when fitted) has long helped identify possible shipping hazards but the returned radar trace requires skilled interpretation. As well, microwave signals may be masked by nearby terrain. Thanks to GPS, your position may be accurately known but the intentions of the “tanker on my port bow!” (suddenly appearing around a headland or looming out of the fog) may be a mystery. VHF voice communication may help clarify things but evasive action takes precious time – especially in congested waters. Aside from the ever-present dangers of weather, reefs and pirates, mariners have to increasingly contend with the possibility of accidentally colliding with each other. The English Channel is so crowded with sea traffic that old salts swear white lines and traffic lights may soon be needed to prevent collisions! When compared with aircraft, vessel speeds are orders of magnitudes slower. But aircraft have the third dimension available to climb or dive to avoid each other – ships naturally work in a more restrictive 2D environment and may also need several This ship parking area is off the port of Newcastle, NSW. At left is a Google Earth overlay showing the ships lucky enough to have entered the Hunter River, while the queue at right shows those still waiting. Do you reckon the captain of one vessel might have got bored waiting and decided to do a hot lap to keep the crew busy? 14  Silicon Chip siliconchip.com.au On the left a “ShipPlotter” example shows single ship AIS details, plotted against a low resolution shoreline sourced from www.sailwx.info Detailed marine charts can be costly, although the 1:250,000 global coastline extractions (freely available as “mapgen” downloads from http://rimmer.ngdc.noaa.gov/) may be satisfactory for shoreside users. nautical miles to come to a stop, go astern or even to make an evasive turn. Automatic Identification System (AIS) An amateur radio APRS (Automatic Packet Reporting System) GPS-based technique has been in use since the 1980s and it’s tempting to think such enthusiasts paved the way for commercial services again – much as amateurs did for “useless” shortwave broadcasting back in the 1920s. ACARS (Aircraft Communications Addressing and Reporting System) began about 1990 and by the late 1990s an international shipboard based collision avoidance positioning system emerged. This marine development has grown into perhaps the most significant navigational safety technology since the introduction of radar. AIS is strictly called UAIS (Universal Automatic Identification System ) but the “U” is often dropped to make it simpler. This wireless technology enables commercial vessels to “see” and clearly identify each other, whatever the conditions (night, fog, storms, congestion). AIS does this by continuously transmitting a vessel’s identity, position, speed and course to all other nearby AIS-equipped vessels or shore stations within VHF range (typically 20 nautical miles or ~ 30km). These low-power and low-speed data signals are openly sent on VHF marine channels 87B (161.975MHz) and 88B (162.025MHz) as brief (~30ms) 9600 bps data bursts and can siliconchip.com.au be readily received and decoded by others for textual or graphical display. So-called Class “A” AIS transponders have been compulsory on vessels over 300 tonnes since 2004 but even smaller leisure craft are now fitting the less informative “Class B” version as part of their e-navigation tools. AIS acceptance and adoption has been very rapid and current worldwide usage is already (mid 2009) estimated at over 40,000 vessels. AIS benefits Although radar and GPS may be thought adequate instruments, there are seven major areas where AIS improves over them: • Longer wavelength – AIS can “see” targets around islands and capes in coastal waters (as microwave radar doesn’t penetrate hills etc) • Ships identified – AIS “translates” radar echoes into ship names and types - useful when calling them on VHF! • More information – AIS improves prediction of a target’s intentions by taking into account its course and rate of turn (ROT). • More range – at sea AIS receivers typically cover to the horizon. • Two-way information – it alerts others to your vessel’s nature and intentions. • Low power – only small transmitters are needed– typically just 2-12 watts (radar is much higher power and has intricate moving parts). • Inshore vessel information can be gained, perhaps globally via the web. Typically the end result can be echarted displays showing details of all AIS-enabled craft within VHF range, along with their course and speed and Decoding software,such as NMEA Plus (trial download) or online via http://rl.se/aivdm, conveniently allows the cryptic AIS data messages to be shown as plain text. Although useful when first testing ones AIS receiving setup, graphical displays may be naturally more enlightening. August 2009  15 Rottnest Island, off Perth/Fremantle (WA), with the Swan River at right. This image comes from www.marinetraffic. com Below is an extracted chart of the same area sourced via NOAA’s free 1:250,000 global coastline resource (http://rimmer.nadc. noaa.gov/). “NavMonPc” can AIS-read and zoom these mapgen format charts. even if they are at anchor or berthed. Although essentially minimising the risk of collision, AIS allows harbour facilities to be productively managed and it’s also useful for marine search and rescue operations (SAR aircraft now increasingly carry AIS), since it can identify and exactly pinpoint the position of an AIS-transmitting ship in distress. AIS information details At its most basic level, an AIS transmitter just continually sends the host vessel’s call sign and GPS position, alerting others to its whereabouts. An intricate method of time sharing the radio channel ensures that even with a large number of vessels nearby, blocking of individual transmissions is unlikely. AIS ships typically automatically transmit dynamic voyage information at intervals of between 2 and 12 seconds (depending on speed and proximity to others), or every few minutes if at anchor. Details include: • MMSI number (Maritime Mobile Service Identity - a series of nine digits) • Navigation status, eg, ‘at anchor’ or ‘underway’ • Ground speed, from 0 to 102 knots in steps of 0.1 knots • Rate of turn, 0 to 720 degrees per minute • Position (GPS-sourced latitude and longitude) • Heading and Course over Ground (COG) • Time stamp. Every six minutes vessel information is also transmitted, typically: • Callsign • Ship’s name and unique ID number • Type of ship • Beam (width), length and draught • Onboard GPS antenna location Further voyage related information such as cargo, destination, ETA and route plan, short messages etc, is generally manually entered and updated by the bridge team. Rusty English officers are prone to entering such amusing typos as Sidney instead of Sydney! Nature of AIS data Two-way ship-to-ship and shipto-shore AIS is usually preferred by mariners, as it allows invaluable information to be automatically exchanged between all AIS-enabled craft, maritime traffic stations, coastguard authorities and even buoys and lighthouses. However, such equipment and its professional installation can run to several thousand dollars. Dedicated AIS sets pick the 9600 You might expect to find a lot more ships in what Cook described as one of the world’s great harbours . . . but ever since the NSW government’s rather questionable decision to close Sydney Harbour as a working port, five vessels is about it! 16  Silicon Chip siliconchip.com.au bps GMSK (Gaussian Minimum Shift Keying) FM signal off the receiver’s discriminator and process the entire 25kHz data bandwidth before later narrowing occurs. GMSK (which is also most notably used in the GSM cellular system) enjoys the impulse noise immunity of FSK (Frequency Shift Keying) but the digital data stream is first filtered, thereby yielding high spectral efficiency. If you live near a seaport and have a NBFM (narrow band FM) receiver covering the 161.975MHz and 162.025MHz AIS frequencies (either will do), the brief data bursts arising from nearby commercial ships, boats and ferries can usually be heard as scratchy “pops”. Signals are often quite weak, so the receiver squelch may need to be opened. Unfortunately, in most scanners receiver filters and de-emphasis circuits trim off much of the incoming signal’s intelligence, limiting raw audio decoding. However, it’s feasible to modify even cheap VHF receivers and scanners to make them more acceptable for AIS service without compromising “normal” usage. We show details on how to do this to a typical scanner shortly, with decoding via PC soundcard. The conversion is straightforward on even older VHF scanners and a comprehensive resource site www. Vessel tracks, which fade after selectable times on plotting programs, offer outstanding course insights. Although the AIS course data is near real time, it may be some minutes before ships transmit their name and voyage details. Google Earth pictures are all very pretty but a simple graphical screen, as seen here, is often far better to view ship details and paths without the clutter of buildings. siliconchip.com.au Stats from a Sydney AIS station feeding into www.marinetraffic. com. Freakish AIS reception from far offshore usually relates to VHF tropospheric ducting – common in summer (and at night) when hot dry settled anticyclones overlay cooler, moist ocean air. NSW endured a heatwave early February 2009 ! discriminator.nl/ details the technique for hundreds of different VHF sets. Modern, more upmarket VHF receivers increasingly offer this “discriminator tap” output for direct soundcard input of the raw data. Such direct access to raw data signals may be useful for other digital modes as well – soundcard data decoding is very well established! NMEA Just as modern aircraft are predominantly “fly-by-wire”, modern ships have long enjoyed all-electronic “glass bridges”. The National Marine Electronics Association (NMEA) has developed a specification to suit. Specialised AIS receivers (such as the Smart Radio SR161) will probably include an NMEA port for direct interfacing to various pieces of marine electronic equipment, allowing information to be automatically sent between computers, GPS, radar, echo sounders, chart plotters and the like. Although cryptic, for most purposes NMEA can be considered an RS232compatible 4800 bps, 8 data bits, no parity and one stop bit (4800,8,N,1) protocol. However AIS encoding assigns each ASCII character to 6 binary bits (unlike normal ASCII which uses 8 bits). Here are typical 64-bit plain text AIS data strings – !AIVDM,1,1,,B,1INS<8<at>P001cnWFEdSmh00bT0000,0*38 !AIVDO,1,1,,A,100000002lP7NcvM<at>jupq79`0000,0*3A It’s certainly not easy to make sense of these! An on line NMEA sentence decoder at http://rl.se/aivdm relates the first to an anchored ship near Athens (Greece) at latitude 37.91 N , longitude 23.56 E, while the second vessel travels through the English Channel at a heady 18 knots. (AIVDM = other vessels, while AIVDO means your own ship.) Fortunately there’s no need to sweat the NMEA decoding! Convenient software is available, both for online and local use, that allows smooth PC decoding (and perhaps even plotting) of the shipping data contained in the cryptic NMEA AIS sentences. Shore-side reception and decoding. Let’s imagine you’re based near the busy seaport of Fremantle (WA) and are now interested in setting up a costeffective AIS monitor. As any “Freo” resident will confirm, even with a global downturn, dozens of ships continually ply the Swan River mouth between the mainland and offshore Rottnest Island. What ARE they? Given the open and informative nature of AIS, such interest has soared amongst enthusiasts keen to monitor local shipping moveAugust 2009  17 The Ship on the First Floor When Stan Swan sent his draft and pictures over for this feature, we were intrigued to find a ship “at anchor” a little north-west of Manly, on Sydney’s Northern Beaches. Those who know the area – as we do (very well!) – will know that there is a lagoon a little north-west of Manly but anything higher than about 30cm would not get through the pipe to the ocean. There’s also a dam in the hills above Manly – but we doubted any of small pleasure craft which sometimes use the dam would have AIS fitted. On closer examination, we found that the “ship” was actually “anchored” in a street in Brookvale, only a couple of hundred metres from the SILICON CHIP offices. Then Stan had another look at the data and found the “ship” was actually “under test” and appeared to be tacking back and forth on the first floor of an office building. In fact, he managed to print out the track of the ship, shown below. It certainly shows the accuracy of the GPS tracking signal which is part of AIS! Umm . . . maybe the AIS transmitter should have been turned off or at least fed into a dummy load? 18  Silicon Chip ments – both ashore and when afloat. Before embarking on a full AIS quest it’s first worthwhile experimenting with available VHF receivers (and perhaps simple antenna) to see if 161.975MHz/162.025MHz signals can even be heard locally. As the two AIS channels are marine hi-band VHF ones, almost any VHF radio or old scanner will normally receive them. Cheap US “Weather Band” receivers (~162.500MHz) are so near the AIS frequencies that retuning to suit may even be possible, as may tweaking older two metre (144-145MHz) ham band gear. However, some older VHF receivers may be insensitive, subject to interference or prone to drifting, making full AIS decoding performance possibly frustrating. Dedicated AIS commercial transponder and charting setups can cost many thousands of dollars and best suit the professional or well-heeled. Assuming signals have been detected, more cost effective approaches hence may tempt. 1. Purchase or construction. Aside from just buying a dedicated AIS receiver, making one’s own complete receiver/decoder is not impossible. Several AIS-capable ICs are available (most notably CML’s CMX7032 and CMX7042) to handle all the data massaging – with just a 162MHz RF front-end needed. However such a constructional challenge best suits the real enthusiast, even then one with a reasonable level of skill. So both landlubber ship followers and small vessels keen to receive and decode AIS are advised to look at simpler (and cheaper) options. 2. Discriminator tap + soundcard. As outlined overleaf, basic local AIS reception really only requires the following, with most of the (Windows) software free: • A sensitive, stable ~162MHz VHF receiver with discriminator output (see below) • A suitable VHF antenna (the higher the better - refer “Slim JIM” below) • An mono-to-stereo audio cable between your receiver and PC soundcard input • A Windows PC with 16-bit soundcard – even older laptops will do fine. • Soundcard demodulating and NMEA producing software (AISMon 2.2.0) • A virtual serial port program (VSPD XP5) to feed the decoding program • Either decoding software to turn NMEA strings into plain text (NMEA Plus), or • Simple graphical software to e-chart the NMEA output (NavMonPc) Although increasingly considered a cartographic display norm, Google Earth-style charting of local shipping movements requires powerful software and perhaps local e-charts, both of which can be costly. Naturally a web connection may ease this but remote coastal sites or underway vessels may not enjoy this convenience. The esteemed “ShipPlotter” (Portuguese; 21 day trial then around $50) provides acceptable displays, including linked satellite views and it directly handles the soundcard signal processing and NMEA feeds. In spite of these processing needs, almost any PC will do, as the AIS data handling is relatively pedestrian – there’s even a Win98 version. Although there are numerous other tracking programs, ShipPlotter is presently considered the best value AIS package but it has near overwhelming features with a steep learning curve. Even the alternative (and free) “SeaClear” may take days to fine-tune soundcard settings and charts to your needs. In contrast the simpler (but comprehensive, global and free) 1:250,000 coastline chart extractions used by NavMonPc may better suit. Remember that ships naturally are at sea and Google Earth terrestrial details may hence be incidental (most Google Earth satpics don’t go very far out to sea). 3. Web Server and on line display Although this looks more ambitious, in fact setup is streamlined compared with the 2nd option, as such dedicated sites as www.marinetraffic.com (University of the Aegean, Greece) handle much of the final NMEA decoding and graphical display. Naturally internet access is necessary. Both you and global ship watchers can monitor real-time marine traffic while half a world away (and miles from the ocean) in Alice Springs. That’s right – no receiver is needed! Web-served AIS display viewing is highly recommended initially, as the nature and variety of zoomable graphical ship tracking in popular locations will be quickly experienced. siliconchip.com.au Getting your PC to work its soundcard decoding magic requires three linked programs – an NMEA decoder, com port emulator and AIS displayer. AISMon 2.2.0 has been found a robust initial NMEA decoder, with its blue signal input bar invaluable for audio level setting. Click a 48000 sample rate, 4800 baud rate and serial output on perhaps COM1. Decoded NMEA file saving (and even an internet feed address) can be set from here too – this may be handy for examining the NMEA strings. Connect the discriminator tap to sound card input cable and click Start Monitoring – the level should show mid range blue bars. Sync’s and Message ID numbers should soon appear, with Demodulator Counts (100% is best) often relating to soundcard overload, distant ships or a poor local antenna. Once verified as working this program can be minimized. VSPD – a Virtual Serial Port Driver (14 day trial however) next must be run to provide com port pairs. Com1 from the AisMon feed is simply paired to give a Com3 output. Numerous emulator offerings exist and programs such VSPE (free) may well suit. NavMonPc, a comprehensive (but lean) e-navigation program completes the chain. Start this program, select File and set Serial Channel A as Com3 4800 baud. Clicking Done should finally display decoded NMEA messages as they arrive – recheck all earlier settings and connections if they don’t. Options allows entering (as DD MM.mmm) your local latitude and longitude – just approximate values will initially do – with Use This Position. Clicking AIS then gives a circular display, with targets shown as triangles, although true vessel outlines can be selected at high zoom levels if the bridge crew have entered them correctly. Local NOAA charts can be obtained from http://rimmer.ngdc.noaa.gov/. Tweak your receiving locality details if need be. After all the hard work, spend some time enjoying the settings, tracks and zoom levels! This may even be all you need, especially if living inland beyond marine VHF range. You can help contribute data! Our Fremantle example is one such area that web-based AIS info is lacking – at the time of writing, virtually none of the WA coast (including the very busy Pilbara) had web-based AIS coverage. This will no doubt change as more and more enthusiasts contribute their received AIS data to the world wide web. Of course, not having web-based AIS doesn’t stop you receiving it direct – and if you are at a fixed site with VHF AIS reception, you can become active in supplying YOUR soundcardgathered AIS data to a global audience. By altruistically providing your own local AIS web feed you can help extend the global AIS footprint. All that’s required is to enter the IP port address supplied by the hosting service and ensure a reliable upload feed. A modest few megabytes per day of uploaded data seems typical of harbours such as Wellington and although essentially just a public service, bensiliconchip.com.au eficial educational and promotional spinoffs may result. Serious ship watchers who are keen to provide coastal coverage in busy regions still not served may even manage a free professional AIS receiver from site hosts such as www.vesseltracker. com. Their motivation behind such largesse is no doubt commercial! Web monitoring concerns Although enthusiasm is globally very high (especially in Europe) for AIS adoption, both at the super-tanker and recreational boating level, concerns have been raised over web-based AIS data availability. The International Maritime Organization (IMO) Safety Committee especially feels that web publication of freely-available AIS-generated ship data could be detrimental to the safety and security of ships and port facilities. Given recent piracy, it’s indeed feasible that criminals may be monitoring inshore ship movements with devious intent. But ships in global trouble spots can, of course, simply turn off their AIS transmitter or remove sensitive voyage entries – or even spoof their true identity (eg, a cruise liner or oil tanker anywhere near the Somali coast appears on AIS to be a destroyer!). Taken overall, public AIS information, both locally-monitored or web-based, seems so informative that beneficial aspects win the day. Just being able to pop into an internet café and web-locate a moored dockland vessel may save the bacon of lost crew floundering around in the fog as sailing time approaches! Web-published information is not, of course, intended to enhance safety at sea. Any internet-provided AIS data may be obsolete, in error or incomplete and best suits general shore-side informative purposes. On-board seamanship and navigation aids are naturally still required. Article links and AIS resources are hosted at www.manuka.orconhosting. net.nz/ais.htm OVERLEAF: How to modify a Uniden scanner (without affecting its normal usage!) to receive 160MHz AIS transmissions. August 2009  19