Land-based infrasound recording is not particularly complicated; you can put the sensors anywhere. Not so in the oceans of the Southern Hemisphere: Sensors can only be placed on most small, lonely islands, so coverage is poor.
And, says den Ouden, out in the ocean, “the huge turbulence of the waves” creates a lot of unwanted noise. Some of these irritating infrasounds occur when crashing ocean surface waves interact. Den Ouden said: “The ocean begins to rise and fall in a rhythm. The sea acts like a giant megaphone, blowing energy into the atmosphere that travels up and through the water, toward land, like an invisible tidal wave. Other oceanic infrasound waves are less problematic but more mysterious: The motion of the sea causes vibrations in the atmosphere that radiate straight up. But these waves have proven so difficult to detect that their existence has long been an open question.
This set of infrasound waves, technically known as the microbarom, is called “the voice of the sea. “Most researchers want to submerge it. “We try to get rid of the microbarom signal, because we are interested in explosions,” says Iezzi.
Ideally, marine infrasound detectors could not only fill the vast coverage gap, but also record the microbaroms well enough that, with the help of filtering software, they could be suppressed. effectively. But where would you put these detectors? Boat will not work. “The problem with them is that they are always moving up and down,” says Lamb — and that would mess up the recording. Balloons have been used to record infrasound waves over land, but their flight path over the sea would be too unpredictable to be used. (However, they will be useful for recording lightning strikes, earthquakes, and volcanic eruptions on Venus, because the surface of this evil twin earth is so hot that any tools placed on the ground there will quickly melt. Or, at least, too hot.)
The open ocean is “an incredibly challenging place to record sound,” says Bowman, “in fact so challenging, that if you asked me before looking at this article, I would have said basically can not.”
When it happens, Samantha Patrick, a seabird ecologist at the University of Liverpool, was curious about the ability of seabirds to navigate using infrasound waves. After conversing with den Ouden and his weather and geophysics colleagues, they developed a curious idea: Why not attach microbarom detectors to birds? And not just any bird: wandering albatross. Their wingspans, which can be 11 feet long, are longer than any human height. This allows them to spend considerable time simply floating in the air currents over open water, something that conserves energy as they embark on foraging trips. Not only do they fly over large isolated seas, but they also don’t dive into the water, so any sensors mounted on them won’t get particularly wet.
In succinct order, the researchers built the ultra-small ultrasonic sensors and fit them into bags — packages that aren’t too heavy for a TV remote. It’s interesting to imagine these bags being attached to the way a school kid carries a backpack, it wouldn’t need to be complicated. Instead, the bags were simply taped to the backs of the avian assistants with some duct tape.
Last year, the team went to the Crozet archipelago, a small landmass in France’s sub-Antarctic region where wandering albatrosses love to nest. But how, pray says, do you get the seagulls to cooperate? With one very special hug, obviously — something that prevents any slapping and pecking that could cause injury. “They don’t really have carnivores – certainly no natural predators,” said Patrick, who helped with the research team. “So you literally just walk up to it, and then you put your hand on its bill, and then you have to hug it, because it’s so big. You hug it and lift it out of the nest, then one person holds it, and then the other puts duct tape on their back. “
