Mar_Apr_PCC_2017_Web

Terry Brase
Educational Consultant, Former
Precision Agriculture Educator and
Author
Twenty years ago it was hard to convince
some west coast growers that
RTK was necessary. After all, that was
just something that was used by those
large Midwest growers that had thousand
acre fields to manage. But the
whole concept of RTK is high accuracy
(possibly sub-inch) and precision; that
applies to large and small fields alike.
At West Hills College, the Farm of
the Future was designed and built to
serve as a practical learning farm for
students but also to serve the agricultural
community as a model demonstrating
emerging technologies and
how they could be applied to farms
in the Central Valley. To do this and
as part of the precision ag classes, we
provide examples of RTK GPS.
RTK stands for Real Time Kinematic
and is a type of correction for
GPS. The name comes from surveying
and refers to its ability to maintain the
calculation of a high accuracy position
while on the move. Previously a surveyor
would have to be in one position
for an extended length of time to get a
high accuracy position. Autonomous
GPS (GPS without any corrections)
at best has only 10 foot accuracy, not
accurate enough to determine the
location of specific trees, vines, tissue
samples, irrigation controls, or pest
locations. RTK provides the highest
level of accuracy and repeatability for a
position.
There are many methods of correcting
GPS; Wide Area Augmentation
System (WAAS), satellites, AM beacon
receivers, and others. They all work in
a similar way. All correction is based
on having at least two GPS units:
one serving as a “base” and the other
serving as a “rover”. The GPS used as
a “base” station is at a fixed location
in which the coordinates are known.
Since the base GPS unit is on this
known location, it is able to calculate
distance and direction of the error
included in the GPS calculated position.
This difference between positions
is known as an “error differential”. This
Continued on Page 26
Author with the Trimble mobile RTK. Includes the tripod, GNSS antenna (large
disk centered in tripod), receiver (Yellow box mounted on leg of tripod), SiteNet
transmitting radio and antenna (tall antenna and yellow cylinder to the left
of author), and display (held by author). Note abundance of cabling for data
transfer between devices.
March/April 2017 www.progressivecrop.com Page 25
Photo Credit: Terry Brase