July 2000 Articles
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From The Agri-Data Management Corner
By Gary Grimm
Agri-Data Management Manager
Well, another two months have slipped away and technology continues to change. In the last newsletter I wrote about the development of the WAAS system and what that will mean to precision agriculture once it is up and running. Today I will report on another development that will effect GPS technology that you may or may not heard of.
Since the development of the Global Positioning System (GPS), the government has induce an error in the raw signal through the use of Selective Availability (SA). With SA turned on, a user of GPS with no differential correction could not expect to get any better accuracy than 100 meters (about 300 feet). Today, that same user could achieve an accuracy of 20 meters (roughly 60 feet). The reason for this is because on the first of May the United States Government made the decision to discontinue the use of SA.
As reported in Commerce News from the US Department of Commerce igeb.gov/sa/benefits.shtml, the decision was made to accelerate the acceptance and use of the GPS system in certain industries as well as stimulate an already estimated $8 billion GPS market. The areas that will directly benefit from this move will be transportation, emergency response, land, recreation and space. In these sectors, an accuracy of 60 feet will be sufficient.
This leads to the topic of discussion; is there still a need for differential correction? At first glance one may tend to say no. The accuracy of a GPS receiver with no differential correction on any given day looks pretty good. To see an example of this, visit the web page www.mapshots.com/examples/sa.htm. However, repeatability from week to week and year to year becomes the real question. Accuracy of GPS is effected by more than SA alone. Atmospheric distortion and the position of satellites at any given time, just to mention a couple, will degrade the accuracy of the GPS signal. With this in mind, the correct answer to the question is yes, there is still a need for differential correction. If your goal is to get back to your favorite fishing hole year after year, the elimination of SA will be of great benefit. But, if your goal is to drive to an area of a field with any degree of certainty to pull a soil sample, you will still need access to some type of differential correction.
One thing is for sure, developments in technology will continue to change the world of precision farming. Can you imagine what will be available to us in five or ten years. I for one am excited about the possibilities!
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