Hemisphere GPS MBX-4, User Manual

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12
1: Introduction
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.
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 or using special antennas
and GPS equipment can help to reduce the impact of multipath. For
most consumer-level applications, a small amount of multipath is
tolerable.
The quality of a GPS receiver has a dramatic influence on positioning
accuracy. Consumer-based GPS products, such as many affordable
handheld and fixed-mount receivers, typically operate with an accuracy
of 2 to 5 meters horizontally 95% of the time. The accuracy of a
particular product depends on the specific receiver’s performance
characteristics. Higher accuracy GPS receivers are able to achieve up to
1 meter of horizontal accuracy 95% of the time using real-time DGPS
transmissions.