Growers whose farms have been out of reach of real-time kinematic (RTK) radio towers due to trees or hilly terrain now have an alternate source of high-accuracy GPS correction. Trimble’s VRS Now network, launched in September, is now available in nine states: Alabama, Colorado, Florida, Illinois, Indiana, Iowa, Kentucky, Mississippi and Nebraska.
As with corrections supplied by conventional RTK radio towers, Trimble VRS network corrections provide sub-inch repeatable GPS positioning for precision farming operations such as tillage, planting, spraying and field preparation. But it is designed to offer better signal coverage in areas prone to radio dropouts because corrections are obtained by a cellular modem, rather than through the line-of-sight signals provided by an RTK tower.
“Cellular networks for ag are a relatively new development,” says Chad Pfitzer, RTK and VRS specialist for Trimble Navigation’s Agricultural Division. “Corrections are calculated by reference stations spread out over large areas, 60 miles or so. Corrections get delivered back to the end user via a cell modem to a tractor’s GPS receiver.”
Trimble’s VRS Now system uses a coordinated network of base stations to calculate corrections. “That’s a bit different from CORS [continually operating reference station], which uses one base station or oftentimes several individual base stations that are not coordinated through a central server,” Pfitzer explains.
By coordinating the bases through a server, VRS improves accuracy within a network, regardless of the tractor’s distance from any one individual base station, Pfitzer says. CORS-based systems, in comparison, encounter the same signal degradation parameters as traditional RTK systems do.
A yearly subscription to the Trimble VRS Now service costs $1,200 (GPS) to $1,500 (GNSS) for agricultural applications. For non-Trimble-owned VRS networks, the price is set by the operator.