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Glossary
64 GSR2700 IS Operations Manual
Ionosphere— The layers of ionized air in the atmosphere extending
from 70 kilometers to 700 kilometers and higher. Depending on
frequency, the ionosphere can either block radio signals completely or
change the propagation speed. GPS signals penetrate the ionosphere
but are delayed. This delay induces error in the GPS measurements
that can result in poor survey results. Most GPS receivers/processing
software model the ionosphere to minimize its affects. Also, the
effects of ionosphere can be nearly eliminated by using dual
frequency receivers which can calculate the delay due to ionosphere.
L
L1— The 1575.42 MHz GPS carrier frequency, which contains the
course acquisition (C/A) code, as well as encrypted P-code and
navigation messages used by commercial GPS receivers.
L2— A secondary GPS carrier (at 1227.60 MHz) that contains only the
encrypted P-code.
L-Band— The range of radio frequencies that includes the GPS L1
and L2 carrier frequencies and the OmniSTAR satellite signals.
M
Mask angle— See Elevation mask angle .
Multipath— The reception of a satellite signal both along a direct path
and along one or more reflected paths. Reflecting surfaces near the
GPS antenna cause this type of reflected signal. The resulting signal
results in an incorrect measurement and thus errors in position
estimates. In other words, these are errors caused by the interaction of
the GPS satellite signal and reflections.
N
NMEA— National Marine Electronics Association, an organization
that created an industry standard ASCII log types used by many
receivers.