RTK and Differential Correction Technologies
The success of precision farming implementations is greatly impacted by the accuracy of the GPS signal. The best case scenario for an uncorrected GPS signal is within 10 fleet of its actual location. When used in a precision farming application this really only works for pass-to-pass applications where the slow drift of the GPS signal can ensure that only a few inches of overlap occur. Any field boundaries and the resulting data files can not be reused in months and years to come as the signal will have drifted too make the data useable. These conditions can be improved somewhat by the varying the GPS correction signals that are available.
WAAS & OmniSTAR
WAAS is a satellite based correction source that utilizes ground stations to generate a correction and broadcast it via a radio signal. The correction is derived from combining the data from GPS satellites taking into account the GPS satellite orbit, clock drift and timing delays. It is calculated by ground stations across the US and is broadcast through three geostationary satellites fixed over the equator. Using WAAS will get a user 6 – 8 inch pass-to-pass accuracy. OmniSTAR uses GPS satellite data and ground stations similar to WAAS to derive a multi-station correction to increase accuracy over the service area. OmniSTAR offers two types of service: HP and XP. The HP signal is a higher accuracy solution providing the user 2 – 4 inch pass-to-pass accuracy. The second service is labeled XP and offers the user 3-5 inch pass-to-pass accuracy.
RTK offers users the highest accuracy available in GPS technology. It combines GPS satellite data with a ground station in the same location as the user to broadcast a correction via radio or cellular data connection. The increased accuracy is possible because the ground station is broadcasting from an area within miles of the rover; therefore the conditions of the two are virtually the same negating accuracy compromising differences in the atmosphere. With this technology it is possible to achieve sub-inch pass-to-pass accuracy and year-to-year repeatability.
The year-to-year repeatability aspect of RTK is perhaps the biggest appeal. While sub 6" accuracy of other technologies is perfectly acceptable for most applications, the accuracy is only pass-to-pass and after months and years the location will have drifted enough that monitor data and boundary files can not reused. This requires an operator to drive fields unnecessarily crushing crops and compacting soils.
Messick's operates a small RTK correction network delivered over cellular connections in South Central Pennsylvania. For more details on our service and how it can improve the operation of your precision farming investments, contact a Messick's precision farming expert.