Gooooal! Two Technologies Compete to Sense Soccer Goals

In the 39th minute of a 2010 second-round World Cup soccer game, England's Frank Lampard shot the ball at Germany's goal. The ball hit the crossbar of the goal net, bounced down to the ground and back up to the bar again before the German goalie grabbed it out of harm's way. The officials called it a no-goal, because the ball had not fully crossed the white goal line on the pitch that runs parallel to the cross bar. But it had. Video replay showed clearly that Lampard's shot had hit the ground nearly a third of a meter inside the goal line before bouncing back up. But the call was final, and the Germans had the ball. England lost that game and was eliminated from the World Cup.

Lampard's goal-that-wasn't immediately reignited a debate that has been simmering in soccer for years. Should the sport install goal line technology—sensors that would tell referees exactly when the ball has passed that crucial white line? Many see the England–Germany game as a prime case for why soccer needs to embrace technology. But for a long time, the International Football Association Board (IFAB), which oversees the international rules of soccer, was cold to the idea of adding any kind of technology to the game. Instead, they introduced two new referees to watch the goal line.

With so many players hovering close by, however, those extra refs cannot always see clearly. Case in point was another missed call at this year’s Euro Cup, which used the five-referee system. In the 62nd minute of a crucial game, the Ukrainian striker Marco Devic launched a ball that bounced off England’s goalkeeper and toward the goal line, before an English defender cleared it. The goal referee called it a no-goal, but replays showed the ball crossed the line. The goal would have put Ukraine even with England 1-1, but without it they lost 1-0, and were eliminated from the tournament. Afterward, Sepp Blatter, president of the sport’s governing body, FIFA (Fédération Internationale de Football Association), tweeted: "After last night's match GLT [goal line technology] is no longer an alternative but a necessity."

Before the Euro Cup, the IFAB had changed its mind and gave the green light to try goal line sensors from two of 10 competing companies: GoalRef and Hawkeye. In early July, IFAB approved both technologies, although they will remain optional. FIFA said it will use goal line technology for future matches, including the next World Cup, in 2014 in Brazil.

The two companies have quite different approaches. Hawkeye's system—many details of which are under wraps until after this round of testing ends—is based on the same technology you might have seen at top-tier tennis matches. A series of cameras positioned around the soccer field will watch the ball and calculate its position in the air to determine whether it fully crossed the plane of the goal. If a referee's call on the field is controversial, officials can look at the Hawkeye replay—the same way tennis officials, and fans, can now see precisely whether the ball landed inside, on or outside a line.

GoalRef uses a completely different system. There are no cameras and no high-powered computers crunching video. Instead, GoalRef relies on a low-level magnetic field spanning the goal opening. Wires inside the goal posts generate the field, and wires inside the ball disrupt that field after the ball completely passes through the opening. The system then alerts the referees that the line has been crossed.

The wires in the ball are small and robust enough to survive the impact of being kicked around for 90 minutes, and they weigh so little that a GoalRef ball is indistinguishable from a regular one. "If you don't know that it's a special ball, you cannot decide whether it's normal or one with the special technology," says Rene Duenkler, a scientist with GoalRef. The ball is even approved by FIFA for use in games.

The distinction between these two technologies is that one is camera-based and one is not. And that difference could be the deciding factor. Unlike tennis, where there is almost never any thing or person obstructing the line of sight between the cameras and the ball, soccer presents unique challenges—especially during free kicks and corner kicks. In such situations, 10 players might be close to the goal, making it harder for cameras to unambiguously record when the ball passes the line. Hawkeye declined to comment on its technology, as it is still in the testing phase, but the company's Web site notes that it is dealing with a way to compensate for the problem by using multiple camera angles.

Not everyone is keen on goal line technology. Michel Platini, head of the Union of European Football Associations (UEFA), worried that introduction of this technology would begin a slippery slope toward more intrusions to the game, and he stood staunchly opposed to the technology. So even if UEFA is not on board, FIFA is, and the next international soccer stage will feature a new prop—a technology that will help enforce the line between winners and losers.

This feature is courtesy of Scientific American, our content partner in bringing you everything you'll want to know about the Summer Olympics, and is part of its Winning in the Olympics report.

Rose Eveleth | | READ MORE

Rose Eveleth was a writer for Smart News and a producer/designer/ science writer/ animator based in Brooklyn. Her work has appeared in the New York Times, Scientific American, Story Collider, TED-Ed and OnEarth.