Might this help find missing airplanes, especially those lost at sea?

Might multiple location "listening" for a low frequency sub-harmonic of the Underwater Locator Beacon (ULB) "pinger" work, especially over long-distances? The resulting data would then yield the exact ULB location, via triangulation.

Since low-frequency sound travels farther than high-frequency sound in water, doesn't it make sense to "listen" for a low-frequency component of the ULB ping?

"When triggered by water immersion, the ULB emits an ultrasonic pulse of 37.5 kHz at an interval of once per second".  According to my reasoning, the fundamental frequency of 37.5 kHz would not travel nearly as far as a sub-harmonic of this 37.5 kHz.  From what I read, sound frequencies below 1 kHz can travel thousands of miles.  This is evidenced by whales communicating over thousands of miles.  In fact, the SOFAR channel in the sea can and does carry sound many miles.

Here's how it might work:

1. Submarine or land base could focus on one or more sub-harmonics of the 37.5 KHz beacon frequency, "listening" for the "ping" signature.  Computer analysis could help pick this ping out of other noises.
2. Querying multiple locations that "hear" the ping could achieve triangulation of the source, thereby finding the exact location.  Again computer analysis could help.

Here are some ideas for implementation:

• Low Frequency Hydrophone used in seismic detection.
• Infrasound - 
• "The frequency spectra of the pipe pings shows a sub-harmonic at 500 Hz, a dominant frequency at 1,000 Hz, and harmonics at 1,000 hz intervals up to around 4-5,000 Hz (Foley 2005)...." - Whale locator using hydrophones
• Spread spectrum underwater location beacon system - US 4951263 patent
• Flight Recorder Localization Following at-Sea Plane Crashes
• Frequency spectrum of "pings" at sea
• Sound Surveillance System

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Maybe future ULB could have two pingers or sound actuators.  The standard pinger is at 37.5 kHz, the emergency reply frequency, with a detection range of about 1-2 km.  Another lower frequency pinger or sounder could be added, however, to provide long-distance detection range.  Multiple detections at different locations could triangulate the exact position of the downed aircraft.

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What do you think?  Is this possible?  Would this work for the recent missing-at-sea airplane?

Background Information - 

According to a recent article in National Geographic, there are four ways a plane can be tracked -
Missing Malaysian Plane Spotlights 4 Ways Aircraft Talk to the Ground.

These 4 ways are listed below:

1. Transponders (Aviation)
2. Radar
3. Onboard Computers
4. Black Boxes

A component of Black Boxes is a Underwater Locator Beacon.  This beacon is essentially a audio "pinger" that emits an ultrasonic signal periodically.  This is good but the higher the frequency, the less sound travels underwater.  Thus, the receiver of the pinger signal must be fairly close to the pinger transmitter.

Every sound has a fundamental frequency, harmonics, and subharmonics.  Subharmonics = Undertones

Disclaimer - Article is for information only.