The invention and implementation of the satellite-based radio navigation system known as the Global Positioning System, or GPS, has been one of the best things to hit the maritime navigation field since the sextant. But there’s always good and bad aspects to everything. Let’s face it, most mariners have become, to one degree or another, slaves to the GPS receiver / plotter found on every boat these days. Who amongst us carefully, and without fail, constantly monitors the signal-to-noise ratios or which particular satellites are being tracked and used at any given time, thus determining the accuracy of the fixes? Yes, the manufacturers have improved their products significantly over the years. Most modern receivers will warn you when they lose the DGPS signal and shift to GPS, or if they lose everything and go to dead-reckoning mode. But some do a better job of alerting the watch officer to this fact than others, and not everyone is on the lookout for it in any case.
Relying so heavily on any one technology, however, can have dire consequences if that technology is taken away, especially without warning and at a critical moment. This can take the form of a GPS receiver becoming completely and immediately non-functional due to an internal malfunction or an external force such as a power surge or lightning strike. But at least if it craps out all at once you’ll know right away and can turn your attention to the other tools, such as the radar, paper nautical charts and your eyeballs. The bigger danger comes when it malfunctions in a subtle way that you don’t detect until it’s too late. If the GPS tells you a great big whopper of a lie, like that your off the Seychelles when your actually steaming up Buzzards Bay, you’ll probably catch it quite quickly. But if you’re navigating in a narrow channel and trying to stay very close to the edge when it lies to you just a tiny bit you can quickly find yourself aground.
Maybe it’s acting up intermittantly because of a failing or corroded electrical connection, a bad ground, or antennae that are slowly dying. But there is another possibility that few ever consider: storms in outer space. When the sun spins off huge solar storms, massive bursts of electromagnetic radiation, at us it can disturb Earth’s magnetic field and severely degrade the performance of your GPS (or Loran). Having some advance warning of these events is important and NOAA can help. Go to Space Weather Now and sign up for their automated-email space weather forecasts and alerts. Go to the Navigation Systems page to learn more about how and why GPS and LORAN-C are affected. Check the forecast here.
It’s not necessary for you to understand or remember all of the physics behind it, although there’s plenty of technical information if you want it, just that it happens and can have a detrimental effect on your navigation receivers. The alerts from NOAA will give you the heads-up you need to expect and keep an eye out for potential unreliability in the accuracy of the information that you receive. That alone may be all you need to avoid trouble.