Why Pings Are Tough To Hear

ocean shieldTwitter just exploded with news of more pings, presumably from MH370, being heard by Australia’s stubby, tech infused, Ocean Shield. The Aussies are sticking to the plan and keeping optimism in check.

Still, no one can mistake the signs. The Malaysian airliner will be found sooner rather than later.

There’s been a lot of ocean talk recently. I know just enough oceanography to be dangerous. It was my favorite course on my way to becoming a meteorologist.

Like the atmosphere, the ocean is not homogeneous on a global scale. We all know ocean temperature varies by location, but so does salinity, current and other properties.

I learned about the ocean’s “thermoclines” before school. Tom Clancy made them a pivotal piece of “The Hunt for Red October.”

Here’s the money graf from Wikipedia:

In the open ocean, the thermocline is characterized by a negative sound speed gradient, making the thermoclines important in submarine warfare because it can reflect active sonar and other acoustic signals. – Wikipedia

Malaysia_Airlines_Boeing_777-2H6ER;_9M-MRG@ZRH;07.08.1998_(4794758296)It is likely anything on the bottom of the Indian Ocean has one or more of these layers between it and the surface. Thermoclines block sound or even act as ducts moving sound far from where it originates.

Sound can mislead as well as lead. The great distance between the Chinese ship that heard pings last weekend and this new discovery is not unexpected. That’s why they’re being methodical, taking it slow, gradually probing farther down. The deeper the listening devices go, the more local the sound.

What’s being heard does not yet lead to a single point on the Indian Ocean’s bottom. Soon.

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