Technology
The Global Positioning System was established and
is run by the US military. It has recently been made freely available
for non-military use and has established itself in many practical applications.
GPS works by utilising a network of satellites
orbiting the earth. This network consists of 24 satellites, 4 in each
orbit equally spaced and 6 orbits in total at 55° inclinations 20200
metres above the earth.
Each satellite emits a unique signal which
is detected by GPs receivers on the ground. At any one time between five
and eleven satellites are detectable. The GPs unit will select the four
most appropriate satellites and then compute position, velocity and time
from simple geometric calculations combined with some very advanced algorithms.
This is the basis on which the field mapping and sample positioning system
operates.
A GPs receiver is carried on the vehicle
mapping the field. This can be linked to an onboard PC to provide real-time
data as the field is being mapped and soil samples taken. Alternatively
the handheld GPs unit can log data for downloading to a PC at a later
date.
The PC mapping software will then produce
an accurate field map with the positions of the various samples taken.
Once the laboratory analysis of the soil is completed the results are
entered into the field map file and and a soil type distribution analysis
is then produced. This file and data is then used by the spreaders for
accurate and efficient spreading of the lime.
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