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Could pen-sized GPS jammers paralyse UK shipping?

Obsolete satnav rivals troll for security pork

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Loran is somewhat better than Decca but it's based on similar 1940s tech. It's only accurate for most navigational purposes - say, for finding your position on a chart - to around 200 metres. As with Decca, however, Loran can be used to return to a given point under similar propagation conditions with accuracy as good as 50 metres. What it can't do is tell you accurately where that point is in terms of coordinates. (This was why traditionalist fishermen liked Decca. They could use their favourite "lanes" to avoid fouling seabed gear such as beam trawls or scallop dredges on wrecks or rocks whose positions weren't accurately laid down. Those who have seen the effects of beam trawls and scallop dredges first-hand are sometimes less convinced of the benefits.)

Loran and Decca are only marginally useful even in the maritime or aviation environments, mainly for longer-haul navigation in areas where they're available. Across much of the world, you have to rely on GPS or dead reckoning. Loran's no good for piloting a ship into a harbour or a plane onto a runway, as GPS or DGPS can be. And it's no real use whatsoever for minicab drivers, truckers etc. trying to find a given street address in an urban environment. Seriously - no matter what VT and the GLAs would like to tell you.

All in all, then, the future doesn't look too rosy for the GLAs' radio-station branch and VT Communications. Commercial shipowners don't want to pay for their stations, and if their protests got noisy enough someone might seriously start taking a look at the light-dues levy and the somewhat anomalous status of Trinity House - straddling as it does the public, private and "third" sectors.

So there's a need for a new source of revenue - and what could be better than the defence budget? Though the MoD is very hard up at the moment, it wouldn't particularly notice the expense of running Loran.

To get defence/security cash, though, you need a scare threat. Hence, the dreaded pen-sized device which could shut down a major container port or oil terminal and paralyse the British economy.

Hold on, though. Your correspondent used to move ships in and out of British harbours for the navy, back when ordinary GPS was SA-crippled and DGPS cost money directly and thus wasn't normally given to you. If it was foggy and you couldn't navigate in and out of harbour visually, you didn't fool about with Decca and nor would you do so with Loran - they just aren't accurate enough for harbour pilotage. You would use radar, like a sensible person.

And that's what the merchant skippers and harbour pilots still do, in the real world. Radar is the real backup for GPS, when operating anywhere near a coast. Far out at sea where you can't navigate by radar, people can't jam your satnav - not without following you around - and anyway, it takes long enough to get anywhere that the weather will clear sooner or later and you can get a fix with your trusty sextant as of old.

As for jamming radar, that's not something you do with a pen-sized device (actually, nor is jamming GPS; but it's true that jamming GPS is relatively simple). You'd be found and switched off easily if you tried that kind of caper on any effective scale.

It's quite disingenuous of VT Communications to tell politicians that they need Loran in case of GPS jamming in harbours, then. And it's probably a bit naughty of the GLAs to imply that they need tax money - either from shipowners, or even less justifiably from ordinary people like you and me - to run DGPS and Loran stations on such a basis. Especially if that cash is to come from the Defence budget, which frankly has quite enough calls on it just now.

On the other hand, if governments are to piss away cash on domestic security panic, Loran is at least more useful than, oh, biometric ID cards, or a nationwide surveillance-cam network, or urban nerve-gas propagation research or airport mind probes. Why don't Umbers and Basker take their pitch along to the Home Office? ®

Lewis Page was a Royal Navy officer from 1993 to 2004. In the early '90s he was navigating officer and precise-nav officer for minewarfare purposes, employing many recondite technologies of the times including Decca, DGPS, Hyperfix et al. He was also a diver, and once spent six months on fishery patrol duties.

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