Sokkia Axis 3, Operation Manual

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16 Axis
3™
Chapter 2 Introduction
2.5.4 Satellites Visible
The number of satellites visible and their geometry in the sky
influences positioning accuracy. The Dilution of Precision
(DOP) describes the strength of location and number of
satellites in view of the receiver. A low DOP indicates a strong
potential for better accuracy than a high DOP. Generally, more
satellites visible to both the reference and remote receivers
results in a lower DOP. Additionally, if the satellites are evenly
spread around the receiver, rather than grouped in a few
regions of the sky, a lower DOP (stronger solution) will result.
2.5.5 MultiPath
Satellite signals received by the GPS receiver by a reflection
from an object can decrease positioning accuracy. These
multipath signals increase the measured range to a satellite as
the signal takes a longer route to the GPS antenna. Certain
precautions will minimize GPS antenna sensitivity to these
reflected signals. Operating away from large reflective
structures such as buildings can help to reduce the impact of
multipath. For most consumer-level applications, a small
amount of multipath is tolerable.
2.6 Using WAAS
2.6.1 Wide Area Augmentation System
(WAAS)
The Wide Area Augmentation System, commonly known as
WAAS, is being developed by the Federal Aviation
Administration (FAA) as an aid to the basic GPS service. It is
specifically designed to provide three-dimensional guidance for
airplanes. WAAS, like GPS itself, is yet another tool available to
civilian users.