Radar is a mature microwave technology typically associated with counting enemy aircraft or, in commercial applications, counting speeding motorists on roadways. But radar systems have also been recruited by farmers for counting fruits often associated with healthy beverages—namely, cranberries.
For years, farmers have relied on somewhat old-fashioned methods of estimating crop yields: They harvest the plants in one square foot of a cranberry bog or marsh and counting the number of cranberries by hand. Even by repeating the process several times and averaging the results of the different counts, this method of calculating crop yields is imprecise and time-consuming, especially when compared with doing it by radar.
Most of the world’s cranberries are grown by Ocean Spray, which is a cooperative of more than 700 farms. Ben Tilberg, an Ocean Spray agricultural scientist, felt that there had to be a better way to estimate crop yields than the laborious counting methods used by the company and its farmers. He reached out to IEEE Fellow and researcher Susan Hagness and her associate researchers at the University of Wisconsin in Madison, and they felt that microwaves could be used in counting the cranberries.
Cranberries typically grow in beds of sand, peat, and gravel flooded with water, known as bogs. Because of the high water content of the fruit, the dielectric constant of each cranberry is much different than the dielectric constants of the surrounding vines and leaves, and the cranberries can be detected through the application of electromagnetic (EM) energy.
Using a prototype microwave sensing system that’s able to scan a small part of a cranberry bog at one time, cranberry farmers can scan about a square foot of a cranberry bog and receive an estimation of the number of cranberries in that section. The prototype transmits radar pulses towards the ground and receives the reflections from the bog, measuring the different plants and fruits according to their dielectric-constant differences.
The prototype cranberry-counting radar system consists of metal waveguide mounted on a PVC support structure that’s mounted over an area to be measured. The research team is already at work on a second-generation system that will be suspended from a boom and transported by truck, allowing farmers to measure spatial variations in a cranberry field for more accurate yields of the entire field.
See “Radar to the Rescue,” The Institute, September 2018, p. 6.