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Greenhouse Gases


Taking moo-surements with lasers and satellites

by Laura Howes
May 27, 2021 | A version of this story appeared in Volume 99, Issue 20


Measuring a carbon hoofprint

A scientist aims a laser pointer at a cow.
Credit: Yang H. Ku/C&EN/Shutterstock
Moo-suring methane: Precise laser measurements can tell researchers about greenhouse gas emissions from cows.

Of all the places Newscripts might expect to see scientists from the National Institute of Standards and Technology (NIST), a feedlot full of cows wouldn’t be the first place we’d look. But that’s where Brian Washburn, Daniel Herman, and colleagues have been lately. Why? To measure cows’ gassy emissions more accurately than ever before, using lasers.

Cows are notorious greenhouse gas emitters: their farts and burps release various gases into the air as they digest their grassy meals. But accurately measuring those emissions in the field, where cows are spaced apart and their emissions are quickly dispersed into the air, has been a challenge. A challenge that the NIST scientists, with their yen for precise metrology, felt they could solve. “We knew we could sense methane really well” using lasers, Herman tells Newscripts, and “methane is a big problem in agriculture.”

The researchers call their portable device the agricomb (Sci. Adv. 2021, DOI: 10.1126/sciadv.abe9765). It is based on a type of spectroscopy called optical frequency combs, which use interfering pulses of light to measure concentrations of trace gases, and is more accurate than conventional setups. Washburn tells Newscripts that his group is dedicated to finding new applications for frequency comb spectroscopy outside a lab. But he admits that if you had asked him 20 years ago, he would not have expected that his expertise would put him in a feedlot using lasers to measure—or moo-sure—methane emissions from cows.

Luckily for their noses, the physicists didn’t have to stay in the feedlot the whole time. The team set up the equipment along the perimeter of an academic feedlot at Kansas State University and headed back to take the measurements from the comfort of NIST’s offices in Colorado. The researchers found that their equipment could detect methane and ammonia at parts-per-million concentrations. Now that the researchers have proved that the agricomb works in a feedlot, their next step is to take the equipment onto pastures, where cattle spend most of their time.

“We want to tell people what’s actually happening,” Herman says. “And right now in the pastures, no one really knows.”


One, moo, three

A satellite focuses on a cow.
A satellite focuses on a cow.
Credit: Yang H. Ku/C&EN/Shutterstock
Cow-nting from space: Satellite pictures can help track animals over large distances.

If you’ve ever thought that counting sheep sounded silly, what about counting cows? Not as a cure for insomnia but as a way to understand how the livestock interacts with another ruminant, called the tule elk?

These elk were reintroduced to Point Reyes National Seashore in California in the 1990s and then strayed into areas used for cow grazing. It wasn’t clear if the elk and cows were getting along with each other, so researchers in ecologist Doug McCauley’s lab at the University of California, Santa Barbara, have been working on a way to see how cows mooooove around in their pastures and around the tagged elk.

Their solution was to use high-resolution satellite images and student power. Around 10 undergraduates became experts in spotting cows and elk in existing satellite images, a skill that this Newscriptster does not have. The scientists labeled “elk” and “cow” on the small collections of pixels they show in their paper, but in truth, it was difficult to tell the difference (Biol. Conserv. 2021, DOI: 10.1016/j.biocon.2021.109086). This is why scientists do the science and Newscripts just reports it.

Luckily, the cow-ncensus is that the cows and elk at Point Reyes seem to be avoiding conflict. The researchers found that while cattle stay in their pastures, the elk mostly avoid these areas and forage elsewhere. Their results also demonstrate that the technique might work for other ecologists who want to track cows and other animals from space. The researchers are now using their student-generated cow-spotting data to train algorithms to detect animals on East African plains.

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