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Determining Direction of Sound During A Search

I recently received an email from a young woman who, along with her hiking partner, was rescued by SAR volunteers after getting lost in the mountains of northern California's Angelo Coast Range Reserve. According to the woman's account, searchers were fairly close all night, yet despite having voice contact with the subjects, they weren't able to locate them until morning.

As the two women huddled together for warmth in the intermittent rain, they periodically saw the SAR team's lights and heard their shouts, though they couldn't make out their words (or vice versa, apparently). Without a light source of their own other than the small screen of a cellphone, which they didn't try to use for signaling, the ladies had no way to indicate their location other than to shout back at searchers.

With what little battery power she had left on the phone, one of the lost hikers made calls to 911 in an attempt to have the dispatcher relay to the searchers where the subjects were in relation to the team's lights and shouts. Eventually, the cellphone went dead, and the shouting continued. Searchers were having a lot of difficulty determining the direction of the subjects' voices in that mountainous terrain.

Having had similar experiences during SAR missions, when it was difficult to pinpoint a subject's location despite being within hearing range, I thought I'd look into the fickleness of sound and how we as searchers can better hone in on the source of that sound without the aid of a visible light source. I didn't find a whole lot.

First, I read an article called The Direction of Sound, which explains the interplay between time lag, wavelength, and tone. This all makes perfect sense, but it's not always so easy in practice.

Then, in another article I came across about auditory perception, the writer states that a listener can acquire more information about the direction of a sound by moving their head, adjusting the orientation until the source of the sound seems to be located out front, where a human's localization sensitivity is greatest. 

So, if searchers stop moving and take time to call back and forth with the subject, turning our heads as we listen to each call, this would be better than continuing to move while exchanging shouts or whistle blows with the person/s we're trying to locate.

I also found an electronic device, a "bionic" ear with a booster dish, which is said to increase sound by up to 40 decibels and apparently is highly directional, allowing the user to locate the source of a sound. Search and rescue is listed as one of its intended uses; however, I've been unable as of yet to find any comments or reviews by a SAR team that's used this technology.

During one search I was on in the company of a SAR K-9, the handler closely watched his dog's ears each time we heard a shout somewhere in the distance. Just as the dog heard the sound, her ears would twitch in a particular direction. Her handler told me this was a very good indication of the direction the sound was coming from.

If anyone has any additional suggestions or feedback on what little I've discovered so far, please leave a comment.