Why GPS and radar don't work underwater and can't assist in finding the lost Titan submersible

• GPS and radar can scout out missing objects on Earth's surface but are no match for the ocean.
• Water absorbs electromagnetic radiation, which is why sonar tech using sound waves is necessary.

US and Canadian authorities are searching for a submersible, Titan, that went missing on Sunday. It's become an increasingly tense race to find the vessel and rescue its passengers before oxygen supplies run out.

The five passengers aboard were diving to visit the wreck of the Titanic, located about 12,500 feet below the ocean's surface. The descent is supposed to take about 2½ hours, but about an hour and 45 minutes into its descent, the submersible went silent, CNN reported. No one knows where it is.

This speaks to just how extremely difficult it is to find anything underwater, whether it's the size of the Titanic or a small 21-foot-long submersible. It's not like you can simply turn on a GPS tracking system.

Why GPS does not work underwater

Water and air are two very different mediums through which communication signals travel.

On a molecular level, water is denser. Though you can't see them, air contains about 4.4x10²⁰ molecules per cubic inch of atmosphere at sea level. Water, by comparison, has about 1,000 times more, 5×10²³ molecules per cubic inch.

And all those extra molecules get in the way, interact, and absorb the electromagnetic waves that tracking systems like GPS and radar use. So when you get to any significant depth, GPS and similar technology won't work.

For a similar reason, that's why the ocean depths are pitch black, devoid of sunlight because the electromagnetic waves from the sun can't penetrate very deep.

Submarines and other underwater vessels have gotten around this issue in the past using sound waves, aka sonar. Sound can actually travel thousands of miles in water without losing its signal.

Sonar works by sending out sound waves that will bounce off objects, which creates an echo. A machine called a sonar transducer then measures the direction and strength of the echo to locate the object.

How authorities are using sonar to search for the missing Titan sub

Rescue ships and aircraft searching for Titan are equipped with sonar, Wired reported.

However, "These sorts of systems aren't very good for looking for something on the seabed," Frank Owen, director of the Australian Navy's submarine escape and rescue project, told Wired.

This sonar equipment only works to a depth of about 1.25 miles (6,600 feet) — half the distance to the Titanic, per Wired. Therefore, if Titan is much deeper, sonar might not be of much use.

That said, sonar devices detected "acoustic feedback," what are being referred to as banging noises, in the search vicinity on Tuesday.

The source of the noise is unclear but three additional boats arrived on the scene to help further search efforts, one of which has side-scanning sonar capabilities designed specifically to search for objects on the ocean floor, per CNN.

However, if Titan is sitting on the seafloor near the sunken Titanic ship, distinguishing sonar signals between it and the gigantic ship will be difficult and may lead to false positives, per Wired.

The Atlantic Ocean covers about 20% of Earth's surface

The Atlantic Ocean covers 74.4 million cubic miles, or about 20% of Earth's surface. It took ocean explorers 73 years to discover the Titanic, and that was just searching for it on the ocean floor.

If the Titanic were floating somewhere between the floor and the surface, that would drastically increase the search area. Instead of dealing with a relatively two-dimensional seafloor, you'd be looking at the seafloor plus all the water on top of it.

For example, a search area that measures 10 by 10 miles, would equate to 100 total square miles. Now, say you're looking within that 100-square-mile region that is within an area 2.5 miles underwater. Now, that 100 square-mile search radius turns into a 250 cubic-mile search area.

That's basically what rescuers are facing with Titan. It's unclear if the submersible is on the seafloor or floating somewhere above it, so search and rescue efforts must consider a much larger search area than they otherwise would if the crew were on land, or even the ocean floor or surface.

Still, the region near and around the Titanic is probably one of the more extensively-explored areas of the Atlantic Ocean.

Humans have only explored roughly 5% of all of Earth's oceans and many of its depths remain a mystery.