ashtech DG16 Reference Manual page 364

Differential processing
GPS measurements can be
differenced between receivers,
satellites, and epochs. Although many
combinations are possible, the present
convention for differential processing of
GPS measurements is to take
differences between receivers (single
difference), then between satellites
(double difference), then between
measurement epochs (triple
difference). A single-difference
measurement between receivers is the
instantaneous difference in phase of
the signal from the same satellite,
measured by two receivers
simultaneously. A double-difference
measurement is the difference for a
chosen reference satellite. A triple-
difference measurement is the
difference between a double difference
at one epoch and the same double
difference at the previous epoch.
Differential (relative) positioning
Determination of relative coordinates of
two or more receivers which are
simultaneously tracking the same
satellites. Dynamic differential
positioning is a real-time calibration
technique achieved by sending
corrections to the roving user from one
or more reference stations. Static
differential GPS involves determining
baseline vectors between pairs of
receivers.
Dilution of Precision (DOP)
A measure of the receiver-satellite(s)
geometry. DOP relates the statistical
accuracy of the GPS measurements to
the statistical accuracy of the solution.
Geometric Dilution of Precision
(GDOP) is composed of Time Dilution
344
of Precision (TDOP); and Position
Dilution of Precision (PDOP), which are
composed of Horizontal Dilution of
Precision (HDOP); and Vertical Dilution
of Precision (VDOP).
DOP
Dilution of Precision
Doppler aiding
The use of Doppler carrier-phase
measurements to smooth code-phase
position measurements.
Doppler shift
An apparent change in signal frequency
which occurs as the transmitter and
receiver move toward or away from one
another.
Double difference
The arithmetic differencing of carrier
phases measured simultaneously by a
pair of receivers tracking the same pair of
satellites. Single differences are
obtained by each receiver from each
satellite; these differences are then
differenced in turn, which essentially
deletes all satellite and receiver clock
errors.
DTD
Distance to Destination
Dynamic positioning
Determination of a timed series of sets of
coordinates for a moving receiver, each
set of coordinates being determined from
a single data sample, and usually
computed in real-time.
DG14 and DG16 Board & Sensor Reference Manual