On a recent sunny afternoon, David Allen was standing by a third-floor window in a research building at the National Institute of Standards and Technology (NIST), holding in his hands a device that looked like a cross between a video camera and a telescope. The NIST campus is in suburban Gaithersburg, Maryland, but looking out the window, Allen could see 24 hectares (60 acres) of tulip tree, oak, hickory and red maple—a remnant of the northeastern hardwood forest that once dominated this landscape.

Allen mounted the device on a tripod and pointed it out the window at the patch of forest below. The device wasn’t a camera, but a type of optical sensor that, if the science bears out, will be able to estimate the rate of photosynthesis—the chemical reaction that enables plants to convert water, carbon dioxide (CO 2 ) and sunlight into food and fiber—from a distance.

That measurement is possible because when plants are photosynthesizing, their leaves emit a very faint glow of infrared light. That glow is called Solar Induced Fluorescence, or SIF, and in recent years, optical sensors for measuring it have advanced dramatically. The sensor that Allen had just mounted on a tripod was one of them.

“If SIF sensors end up working well,” Allen said, “I can imagine an instrument that stares at crops or a forest and has a digital readout on it that says how fast the plant is growing in real time.”

Such a device would revolutionize agriculture, forestry and the study of Earth’s climate and ecosystems.