220 G12 OEM Board & Sensor Reference Manual
SNR because each channel tracks one
satellite continuously.
Multipath
The reception of a signal both along a
direct path and along one or more
reflected paths. The resulting signal
results in an incorrect pseudorange
measurement. The classical example
of multipath is the "ghosting" that
appears on television when an airplane
passes overhead.
Multipath error
A positioning error resulting from
interference between radio waves
which have traveled between the
transmitter and the receiver by two
paths of different electrical lengths.
Multiplexing
A technique used in some GPS
receivers to sequence the signals of
two or more satellites through a single
hardware channel. Multiplexing allows
a receiver to track more satellites than
the number of hardware channels at
the cost of lower effective signal
strength.
Multiplexing channel
A receiver channel which is sequenced
through several satellite signals (each
from a specific satellite at a specific
frequency) at a rate which is
synchronous with the satellite message
bit-rate (50 bits per second, or 20
milliseconds per bit). Thus, one
complete sequence is completed in a
multiple of 20 milliseconds.
NMEA
National Marine Electronics
Association
NV
Non-Volatile. Usually refers to a memory
device that retains data after power is
removed.
Outage
The occurrence in time and space of a
GPS dilution of precision value
exceeding a specified maximum.
Position Dilution of Precision (PDOP)
A unitless figure of merit expressing the
relationship between the error in user
position and the error in satellite position.
Geometrically, POP is proportional to 1
divided by the volume of the pyramid
formed by lines running from the receiver
to four satellites observed. Values
considered 'good' for positioning are
small, say 3. Values greater than 7 are
considered poor. Thus, small PDOP is
associated with widely separated
satellites. PDOP is related to horizontal
and vertical DOP by PDOP
2
= HDOP
2
+
VDOP
2
. Small PDOP is important in
positioning, but much less so in
surveying.
Photogrammetry
An aerial remote sensing technique
whose latest innovations employ a high-
resolution aerial camera with forward
motion compensation and uses GPS
technology for pilot guidance over the
designated photo block(s).
Photogrammetry forms the baseline of
many Geographic Information Systems
(GIS) and Land Information System (LIS)
G12RevD.book Page 220 Tuesday, April 2, 2002 4:33 PM
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