A lot of things can happen in the name of national security: large expenditures of cash, ambitious projects – sometimes even a resurrection.
Don't believe it? Just look at LORAN. In May 2007, a U.S. Department of Defense report stated that China had obtained the capability to disrupt the Global Positioning System (GPS), which boaters use to navigate and the military uses to guide precision weapons. In less than nine months, the Department of Homeland Security announced it was implementing a system to complement GPS. "The enhanced LORAN, or eLORAN, system will be a land-based, independent system and will mitigate any safety, security, or economic effects of a GPS outage or disruption," said press secretary Laura Keehner.
In other words, LORAN is back.
USCG VISUAL INFORMATION SERVERDoes LORAN deserve a new lease on life? You'll think so, if GPS goes out.E FOR ENHANCED
LORAN C, which many boaters relied upon in the days before GPS, was never taken out of service. But it has always been limited by inexact navigation. Just consider its name: LORAN stands for Long Range Navigation.
While GPS gets us within two to seven meters of a target about 95 percent of the time, if you navigate with LORAN, you could be 30 to 200 meters off the mark. That's as much as a quarter of a mile from where your electronics say you are – pretty good compared to a sextant, but not if you're looking for a 100-yard-wide inlet in heavy fog.
This inaccuracy occurs because of the way LORAN works: It measures time differences (that's what TD stands for, in LORAN-speak), in signals of up to 800,000 watts, broadcast from land-based transmitting "chains." Each chain has a master transmitter and a series of secondary transmitters. But land masses distort these signals, which also slow as they travel over land. In addition, LORAN signals can degrade the farther they get from the transmitters, so locations on the fringes of coverage can expect poorer accuracy than those deep inside coverage areas.
This low accuracy occurs even though the U.S. Coast Guard operates 24 LORAN C stations in America and 49 worldwide. Countries such as China, Germany and Russia also operate LORAN C chains. So, does getting more accurate require more stations? Nope. It means making those already in existence better. Upgraded eLORAN transmitters do this by broadcasting an additional channel that includes a swath of supplementary data, including transmitter identification information, the time of transmission and, most important, correctional signals.
Think of eLORAN as WAAS (wide area augmentation system) for LORAN, instead of GPS. Many boaters are familiar with WAAS, because it has been in their GPS units for years. The Federal Aviation Administration needed a way to improve GPS, to ensure perfect navigation for instrument-approach landings. WAAS, which adds correctional signals from land-based transmitters, was the answer. It quickly found its way into marine GPS units, and we boaters benefited from increased accuracy as a result.
The eLORAN signals are much like WAAS in that they provide correctional information with the original LORAN transmission. They also operate on UTC (universal time coordinated, which is essentially GPS atomic clock time), which allows receivers to use LORAN C, eLORAN and GPS signals all at the same time. When the eLORAN signal is in use, it increases accuracy by eight to 20 meters. That's still not nearly as good as a GPS, but it is a whole lot better than LORAN C, and it's good enough to get you through that foggy inlet when GPS goes down.
USCG VISUAL INFORMATION SERVERNineteen of the Coast Guard's 24 LORAN stations in the States are already upgraded and functional.MILITARY RULES
If eLORAN's signal is still inferior to GPS, why bother with it? Can't the military use a different set of satellites to back up the first one? The answer is that GPS is easy to jam, just one of the problems with a satellite-based system. In fact, solar eruptions can also flummox GPS. That's exactly what happened in December 2006. The stronger of two bursts of solar radiation produced 20,000 times more radio emissions than the rest of the sun. These emissions occurred over the same frequency bands at which GPS satellites transmit. As you'd expect, GPS receivers over the sunlit side of Earth were more than a little bit confused.
Scientists can forecast some solar activity, but these flares weren't predicted. And there's even worse news for GPS: The next significant solar flares, forecast for 2011 and 2012, are expected to be 10 times as intense as those in 2006 and last much longer. Signal drops of more than 90 percent for several hours at a time are anticipated, and there's no easy fix.
We also have to worry about simple accidents, because in at least one case, GPS has been jammed unintentionally. During a month-long period in 2002, GPS units didn't work properly in and around Moss Landing Harbor in California. Eventually, the Coast Guard traced the problem to a moored boat featuring a marine UHF TV antenna with a built-in pre-amplifier. The antenna was plugged in to an AC/DC adaptor that constantly fed it power, even when the TV was off, constantly broadcasting a signal that jammed GPS units up to 2,000 feet away.
