Advanced Forms of GPSThe quest for greater and greater
accuracy has spawned an assortment of variations on basic GPS technology. One technique,
called "Differential GPS," involves the use of two ground-based
receivers. One monitors variations in the GPS signal and communicates those variations to
the other receiver. The second receiver can then correct its calculations for better
accuracy.
Another technique called "Carrier-phase GPS" takes advantage of the
GPS signal's carrier signal to improve accuracy. The carrier frequency is much higher than
the GPS signal which means it can be used for more precise timing measurements.
The aviation industry is developing a type of GPS called "Augmented GPS"
which involves the use of a geostationary satellite as a relay station for the
transmission of differential corrections and GPS satellite status information. These
corrections are necessary if GPS is to be used for instrument landings. The geostationary
satellite would provide corrections across an entire continent.
All of these technologies are covered in more detail later in this tutorial.
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