Ashtech Zx Superstation - ashtech Z-Xtreme System Manual

object that lies in the path between the GPS receiver and the satellites will be detri-
mental to the operation of the system. Some objects, such as buildings, will com-
pletely block out the satellites signals. Therefore, GPS can not be used indoors. For
the same reason, GPS cannot be used in tunnels or under water. Other objects will
partially obstruct or reflect/refract the signal, such as trees. Reception of GPS signals
is very difficult in a heavily forested area. In some cases, enough signal can be
observed to compute a rough position. But in virtually every case, the signal is not
clean enough to produce centimeter-level positions. Therefore, RTK is not effective in
the forest.
This is not to say that GPS RTK can only be used in areas with wide-open view of the
sky. RTK can be use effectively and accurately in partially obstructed areas. The trick
is to be able to observe, at any given time, enough satellites to accurately and reliably
compute a position. At any given time and location, 7-10 GPS satellites may be visi-
ble and available for use in RTK surveying. The RTK system does not require this
many satellites to function. Accurate and reliable positions can be determined with 5
satellites properly distributed throughout the sky. Therefore, an obstructed location
can be surveyed if at least 5 satellites can be observed. This makes RTK use possi-
ble along a tree line or against the face of a building but only if that location leaves
enough of the sky open to allow the system to observe at least 5 satellites.

Ashtech ZX SuperStation

The Ashtech solution for RTK surveying is the ZX SuperStation. The ZX SuperStation
includes all required components to perform post-processed and real-time GPS sur-
veys. The ZX SuperStation is powered by the Ashtech Z-Xtreme dual-frequency GPS
receiver. Being a dual-frequency receiver (utilizes satellite signals on both L1 and L2
frequencies), the Z-Xtreme makes your GPS system versatile. When performing
post-processed surveys such as control establishment and densification, the Z-
Xtreme will allow for long separation between base and rover receivers while main-
taining the highest level of accuracy. For RTK surveys, system initialization times are
short and the solution reliable, resulting in high productivity.
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