IEEE Fellow Susan Hagness and her research group at the University of Wisconsin in Madison have applied their expertise in electromagnetics to a number of areas including medical imaging and cancer therapies. Now her team is working on a device to help cranberry growers with the laborious task of counting their fruit.
The current method of estimating cranberry crop yield is to harvest the berries within 1 square foot (929 square centimeters) of a bog or marsh, count them by hand, and extrapolate from there. Because there might be hundreds of berries per square foot, the process can be time-consuming and labor-intensive. Also, the process is imprecise. “There can be numerous varieties of cranberries growing on any given farm, and not all varieties yield the same amount of fruit,” Hagness says.
Growers have been looking for a technological solution to more accurately and efficiently estimate the size and quality of their crop, she says. Two years ago, Ben Tilberg, an Ocean Spray agricultural scientist in Wisconsin, contacted the university with an idea. (Ocean Spray, a cooperative of more than 700 farms, is a leading producer of cranberry products. Its headquarters is in Lakeville, Mass.)
“He was generally familiar with the concept of microwave radar,” Hagness says, “and wanted to see if microwaves could be used to remotely sense the number of berries in the canopy beneath the sensor.”
She worked with IEEE Fellow John Booske, a professor of electrical and computer engineering, and IEEE Graduate Student Member Alex Haufler, a Ph.D. candidate in electrical engineering, both at the University of Wisconsin, to turn Tilberg’s idea into a working prototype. They tested their device last year at two cranberry farms in central Wisconsin. Now they’re working on a second-generation prototype, which they plan to try out this year.
HOW IT WORKS
A popular misconception is that cranberries are grown underwater, Hagness says. They actually grow on dry vines in beds that are layered with sand, peat, and gravel—known as bogs. Typically farmers then flood the bogs. But long before a bog is flooded, farmers and growers, as well as cranberry researchers, want to know how many berries are on those vines.
The team’s current microwave sensing system is composed of a metal waveguide mounted on a PVC support structure that positions it above the canopy. The waveguide sensor transmits electromagnetic waves toward the ground and receives the reflected signal. The device can scan about a square foot at a time.
“Before we set out to develop a first-generation prototype of the cranberry-sensing system, we asked Ben for a bunch of cranberries to study in the lab,” Hagness says. “We sliced them open to measure the dielectric properties of the flesh of the fruit and confirmed that there was a significant dielectric contrast between the high-water-content fruit and the surrounding leaves and vines—about a 3-to-1 ratio.”
The more berries in the canopy, the more water there is for the microwaves to interact with. The system converts the measured signals into an estimate of the number of berries within the sensor’s 1-square-foot field of view.
The team is designing its second-generation prototype to be suspended from a boom and transported by truck to anywhere in the field that a grower wants to observe. Portability is important, Hagness notes, because the farmers want to estimate spatial variations in the berry counts across different growing areas to accurately determine the yield of berries that year.
The university’s work stands to have a significant impact on the cranberry-growing industry in the state. The United States is the world’s top producer, with an annual yield of more than 340,000 metric tons—and more than half of U.S. cranberries are grown in Wisconsin.
“To take our microwave-sensing expertise and apply it to something so relevant to Wisconsin has been really meaningful,” Hagness says.
She says the group isn’t aware of any prior work on cranberry crop assessment done by radar. One farmer in Florida has expressed interest in using the group's technology to count the fruit on citrus trees.
“Going forward we’ll consider working with other growers,” she says, “to see if our technology can be adapted for estimating yield for other crops.”
This article is part of our April 2018 special issue on agtech.