Glossary 219
antenna, to a high degree of accuracy.
However, it has no information number
of waves to the satellite at the time it
started counting. This unknown number
of wavelengths between the satellite
and the antenna is the integer bias
term.
Integrated Doppler
A measurement of Doppler shift
frequency or phase over time.
Ionosphere
Refers to 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. The ionospheric delays can be
predicted using models, though with
relatively poor accuracy, or measured
using two receivers.
Ionospheric delay
A wave propagating through the
ionosphere [which is a
nonhomogeneous (in space and time)
and dispersive medium] experiences
delay. Phase delay depends on
electron content and affects carrier
signals. Group delay depends on
dispersion in the ionosphere as well,
and affects signal modulation (codes).
The phase and group delay are of the
same magnitude but opposite sign.
Julian date
The number of days that have elapsed
since 1 January 4713 B.C. in the Julian
calendar. GPS time zero is defined to be
midnight UTC, Saturday/Sunday, 6
January 1980 at Greenwich. The Julian
date for GPS time zero is 2,444,244.5.
Kinematic surveying
A method which initially solves
wavelength ambiguities and retains the
resulting measurements by maintaining
a lock on a specific number of satellites
throughout the entire surveying period.
L1
The primary L-band signal radiated by
each NAVSTAR satellite at 1575.42
MHz. The Ll beacon is modulated with
the C/A and P codes, and with the NAV
message. L2 is centered at 1227.60
MHz and is modulated with the P code
and the NAV message.
L-band
A nominal portion of the microwave
electro-magnetic spectrum ranging from
390 MHz to 1.55 GHz.
LNA
Low-Noise Amplifier
MSG
RTCM Message
MSL
Mean Sea Level
Multichannel receiver
A receiver containing many independent
channels. Such a receiver offers highest
G12RevD.book Page 219 Tuesday, April 2, 2002 4:33 PM
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