Don’t just trust Sat Nav to find your carp lake!

Every year we get calls from anglers whose GPS systems have directed the many miles from their intended destinations.  Because of this we always recommend you take a good French road map & use it, together with the directions we provide, to at least check your Sat Nav is not taking you miles out of your way.  There’s little doubt they are a fantastic aid… but we trust them completely at our peril.  In this article Chris Dagg, the owner of Notaires & Alder lakes, explains why;

When an elderly couple set off on Christmas day in Oregon to visit friends, they switched on their trusty GPS and followed its instructions to the letter. They may, if asked, have said that they would stake their lives on it – and they nearly did – getting stuck in a snowdrift on a remote logging road for three days before a weak signal from their GPS-enabled phone flagged their location to the emergency services. The problem in this case was not the GPS satellite system but the receiver setup, and especially the unquestioning trust that is placed upon it.

How the GPS receiver determines your position

1 GPS satellites beam a signal with their ID and the time that the signal was sent using four atomic clocks
2 GPS receiver sets its quartz clock from the satellites atomic clock (you get atomic time for free!)
3 GPS receiver has satellite positions in its memory and calculates its position by a process called trilateration which is triangulation in 3 dimensions

Now reports are highlighting two major threats to the ubiquitous GPS system that is not only used for navigation and vehicle tracking, but also many other sectors from distribution to just-in-time manufacturing. It’s not very well known that the timing signals are used to keep phones, networks and even power grids online. The problem arises from the weak signal transmitted by each GPS satellite. This is comparable in power to a car headlamp at 20,000 km. The first threat is natural and the second is technological.


A solar flare (photo courtesy of NASA/JPL-Caltech)

Threat 1 – the sun

Our sun has been on the downswing of its solar cycle for the past 11 years and has now passed the minimum. It is on the upswing with increased solar activity and flares which can interfere with the GPS in two ways. Firstly, the increased electrical noise can simply swamp the weak GPS signals. The second effect is more subtle since the GPS works by triangulating its position from the satellites. The time it takes the signal to travel through the atmosphere is factored into the calculation. However, the outer layer of the atmosphere, the ionosphere, is significantly affected by the variable output from the sun and could add up to 10 meters error.

Threat 2 – hackers!

The other major threat is technological, since because the signal is so weak and the protocol is nïave, (that is it trusts the information that it gets, in the same way that my email believes the sender information that it is given), it is easy with the right equipment and programming to substitute a stronger signal which will bias the GPS into showing its position some distance away from the real location (spoofing). Maritime tests have shown that a ship’s position could be spoofed by 10km or more with the ship reporting its GPS position showing it to be inland. Whilst it is easy to postulate criminal reasons for spoofing, since high value cargoes are tracked with GPS and armoured cars are frequently, targeted the question why anybody would consider spoofing the general public was likened to the early development of computer viruses and malware. There was no obvious reason for clever people to put considerable time and effort into developing these programs but they did – usually to demonstrate their skill to like -minded hackers.

However, even if unscrupulous non-Angling Lines fisheries try to spoof you away from the Notaries’ lakes, we provide excellent written directions to guide you safely to our wonderful lakes and farmhouse accommodation!


2 thoughts on “Don’t just trust Sat Nav to find your carp lake!

  1. Ron Key says:

    Hi Chris, have you been doing a bit of spoofing of your own. I got lost last year, completely missed the motorway, drove a couple of hundred miles across country, and by some strange coincidence ended up at Notaires. Spooky. Worth the trip though!

    Cheers Ron

  2. ChrisDagg says:

    Thanks Ron, it must be your homing instinct for good fishing that got you here!

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