How reliable is the GPS in a time of War?



As we evolve so we become reliant on technology to keep us safe.  It’s not uncommon in the first world to see and hear about blackouts in large cities. Although we have moved on to use electricity more efficiently it still does not stop the havoc that can be caused by natural disaster, mudslides, earthquakes and tsunamis.  We have become so used to having power on 24/7 that there is usually pandemonium when we do lose power to our home, town or city. We wrote about communication in an earlier article but what about the GPS?

It’s not an unknown fact that GPS manufacturers still urge drivers to keep their eyes on the road and not on the GPS – ships and aircraft use GPS as a navigational aid and the navigators of both know the pitfalls of relying on instrumentation.  A ship’s captain told me years back about losing their satnav and only when, in dark cloud and low viz that on seeing another vessel that via VHF they found they were 200 miles off course. In the middle of the ocean this may happen from time to time but it’s a big no no when off coastal waters. This is what happened.  GPS is a navigational tool – it doesn’t drive your car and like your cell phone you need to have your eyes on the road and hands on wheel.  No, the GPS may be a wonderful tool but only at the hands of an experienced navigator.

Like Decca and LORAN before, GPS also has it’s limitations. Decca and Loran use low frequency radio waves which follow the curvature of the earth – transmitters are very powerful, LORAN-C, the newer post war navigational system proved to be very reliable and operates in the 100KHz range. This makes long range navigation simple and accurate but this accuracy is affected by static electricity due to signal degradation. The LORAN-C chain used to be used extensively in the United States. USCG decommissioning started about a year back as GPS rose in popularity. (LORAN maintenance costs are high and the receivers are very expensive). Like any radio device, signal jamming is a huge possibility and in a time of war this is highly probable. GPS use very weak signals to get timing and this is therefore easier to block by malicious users through jamming. The obvious now is whether these jammers are illegal. Unfortunately they aren’t. Jamming was known to take place during Operation Desert Storm but in all likelihood was used by both sides. I recall the jammed transmission in the 80’s from a very well known commercial broadcaster – this broadcaster used powers of up to 500KW on the lower frequencies and the jamming station easily overrode this signal. The intention is only to block out the radiation of intelligence through modulation, even keyed transmissions can easily be blocked such as CW or morse code transmissions. RDF can detect these signals but what can one do in a time of war? GPS transmissions are weak and can easily be jammed – worse still inaccurate data could possibly be propogated.

Looking at just this one simple problem or disadvantage makes me think of WI-FI. Our world is inundated with a communication structure based on WI-FI which has a similar weakness, low signal strength. Besides power klystrons or magnetrons our UHF signals are not very strong, they don’t need to be as long as it’s line of sight. Therein lies the next weakness of GPS and all satellite receivers – loss of signal in a poor environment or weather conditions. A GPS cannot work when the signal is blocked via buildings, mountains – LORAN-C can still operate due to the operational frequency.  Because LORAN proved itself over the last 50 years it’s of no surprise that military are looking into and have manufactured the eLORAN or Enhanced LORAN navigational system. The eLORAN (E-LORAN) transmitters radiate more power than GPS like it’s predecessor, in the magnitude of hundreds of KW, as well as a Differential GPS signal whilst the receiver processes signals from more than one station enhancing accuracy.  At present users of GPS should be advised of the disadvantages of GPS and use it for what it was designed for – a navigational instrument.

(Ed:- As a sidenote, the maintenance company overseeing the Decca Chain in South Africa in the 90’s used the disadvantages of GPS during the operation Desert Storm debacle to attempt winning back the contract from the SA government after it was decided to shut down the network. Sadly this was not proven to be successful and was shut down for good during the year 2000).

Educational: http://edis.ifas.ufl.edu/in653University of Florida

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