Space-Age Farming

07/01/2009 02:00:00 AM

In the meantime, Ehsani says he’s noticed an increased interest among citrus growers, who use handheld units to map citrus groves and assign GPS coordinates to disease-infected trees.

“It used to be used just for variable-rate application and precision ag-types of applications,” Ehsani says. “But now with the diseases we have in citrus, a lot of growers are using it for scouting purposes.”

But not all GPS systems are the same. And matching the correct one to the use is critical if you want to obtain the most out of a system.

Ehsani has conducted several workshops to help citrus growers learn about handheld GPS units, how to use them and how to integrate them with other software.

Photo courtesy of Trimble
An RTK global positioning system provides up to sub-inch accuracy that’s needed for precision planting of crops, such as lettuce.

GPS demystified

GPS receivers use signals from a group of satellites to triangulate the unit’s location. About two dozen satellites orbit the earth twice per day and transmit precise microwave signals. Typically about four to 10 are in view at any one time.

The more satellites on the horizon, the more accurate the collected data, within limits. But a minimum of four are needed to be able to determine exact location.

Basic GPS units—such as the one used in some lightbars—have sub-meter accuracy and are appropriate for uses, such as field cultivation, herbicide spraying and dry fertilizer spreading.

They help prevent overlaps, reduce operator fatigue and increase efficiency. They’re also the least expensive and can be had for less than $1,000 per unit in many cases.

Most GPS units are capable of receiving WAAS—or Wide Area Augmentation System—signals. WAAS is a free differential correction signal that improves the accuracy of GPS systems.

If you farm near a navigable waterway, such as along the Indian River, the Coast Guard maintains beacons that provide similar differential correctional signals.

Growers who use auto-pilot systems or GPS to precisely plant rows or level land use an RTK GPS system. They’ll typically put a portable RTK tower in their fields to fine-tune the satellite signals even further. The result is sub-inch accuracy.

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