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Goal Line Tech – Light versus Radio

goal line tech

Goal line tech uses low frequency radio or cameras to detect when a soccer goal has been scored. No more arguments about “was it in?” 

I have been a big soccer (football) fan since I started coaching with the kids many years ago. In recent years, increasing use has been made of technology at the higher levels of play. We have come a long way since instant replays were introduced on television broadcasts back in the 1960’s.

Today, at major venues, fans can watch replays on large stadium screens. Video assistant referees are also coming into force. VAR can help resolve uncertainty around certain decisions, and are also used for retroactive discipline on certain fouls referees may have missed. Referees and their assistants are also wired for radio communication as the game progresses.

Soccer, or football, has traditionally eschewed technology, but I think that train has left the station for higher tiers where money and prestige are at stake.

Goal line tech is one area that I consider an improvement. Laws of the game state that the ball must be completely across the line for a goal to count. Simple physics tells you that the precise position of a round ball moving at speed is very hard to determine with the naked eye. In part, this is about the viewer’s perspective.

Over the past six years, FIFA has approved and licensed a number of goal line technologies for use in first tier and international competitions. Goal line tech uses two different approaches – visual light and radio signals.

If your read the FIFA Test Manual, you will notice the emphasis on reliability, accuracy and decision speed. Goal line tech must be accurate within ±1.5 cm, roughly an inch, and signal the referee of a goal within seconds.

Goal Line Tech can use Low Frequency Radio

Hawk Eye is the most popular goal line tech. It uses an array of cameras around the goal posts and has the benefit of providing immediate video interpretation for use by broadcasters as well as the referee. Originally developed for cricket and tennis around 20 years ago, camera-based goal line tech has the drawback of requiring at least 25% visibility of the ball. That’s why they use so many cameras, typically 7 to 15, and are very expensive. On the other hand, no modifications are required for the ball.

But the other approach uses radio, or specifically low frequency electromagnetic waves. Sensors are placed around the goal posts and set up a radio curtain across the entrance. Passive reflectors, like in RFID are placed in the soccer ball. As the ball penetrates the plane, currents in the system get effected. This results in an accurate positioning.

goal line tech

EM systems are cheaper than cameras. With GoalRef, three passive loops can be implanted within any soccer ball, while the competing Cairo system requires custom Adidas balls. Here is a detailed description of the various approaches.

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