GPS: Its Uses and Potential Are Growing
Global positioning systems (GPS) are widely available in the agricultural community. Farm uses include:
• mapping yields (GPS + combine yield monitor),
• variable rate planting (GPS + variable rate planting system),
• variable rate lime and fertilizer application (GPS + variable rate controller),
• field mapping for records and insurance purposes (GPS + mapping software), and
• parallel swathing (GPS + navigation tool)
Automated guidance of agricultural vehicles (tractors, combines, sprayers, spreaders) has been motivated by a number of factors—most important is to relieve the operator from continuously making steering adjustments while striving to maintain field equipment or implement performance at an acceptable level. This is not surprising, considering the many functions an operator must monitor, perform, and/or control while operating the vehicle.
The requirements placed on farm-equipment operators have changed drastically with increases in equipment size, power, multiple equipment functions, and speed as well as monitors reporting on specific system performance. These increasing demands on the operator can result in increased errors in function, costs, environmental problems, and operator fatigue.
Foam markers, a widely used technology
Foam markers are the most common form of navigation aid used during fertilizer and pesticide application. The foam is dropped and used to align the applicator during the return pass. Foam markers utilize an air pump to pressurize a tank containing the foaming agent. The pressurized fluid causes the foaming agent to flow into an accumulating chamber. The foam collects in this chamber until the accumulated mass overcomes surface tension, causing a foam blob to fall to the ground.
Most often the foam accumulators are placed at the ends of the applicator boom or, alternately, at the center of the applicator when booms were not utilized, as in the case with spinner-disk granular applicators. Equiment operators use the foam blobs left on the field surface as a navigation aid to know where the applicator has passed.
(Source – http://pubs.ext.vt.edu/442/442-501/442-501_pdf.pdf)