Geoscience Reference
In-Depth Information
PDOP and Number of Satellites for Kinematic GPS Data
RMS3D for Kinematic GPS Data using Single Point Positioning: Meter
11
10
9
8
7
6
5
4
3
2
1
0
20
18
PDOP
Satellite Number
16
14
12
10
8
6
4
2
0
500
1000
1500
2000
2500
3000
500
1000
1500
2000
2500
3000
Seconds
Seconds
RDOP and Number of DD for Kinematic GPS Data
RMS3D for Kinematic GPS Data: Meter
0.3
8
Number of obs.
RDOP
7
0.25
6
0.2
5
0.15
4
3
0.1
2
0.05
1
0
0
500
1000
1500
2000
2500
3000
500
1000
1500
2000
2500
3000
Seconds
Seconds
fIGURe 9.7
Position dilution of precision (PDOP) and the number of satellites observed (top left) and the
corresponding three-dimensional standard deviation for GPS point positioning with range observation (top
right); relative dilution of precision (RDOP) and the number of differential observations (bottom left) and the
corresponding three-dimensional standard deviation for GPS relative positioning with carrier phase observa-
tions (bottom right).
(see Section 9.7.1.2). SA levels were set to zero on May 2, 2000, at 04:00 UT (Universal Time). For
more information on GPS error sources, the reader is referred to Hofman-Wellenhof et al. (2001)
and Lachapelle (1990).
9.6 MAtheMAtICAl ModelS of pSeUdoRAnGe And CARRIeR
phASe obSeRvAbleS
Pseudorange is a
geometric range between the transmitter and the receiver, distorted by the propa-
gation media and the lack of synchronization between the satellite and the receiver clocks. It is
recovered from the measured time difference
between the epoch of the signal transmission and the
epoch of its reception by the receiver. The actual time measurement is performed with the use of the
PRN code. In principle, the receiver and the satellite generate the same PRN sequence. The arriv-
ing signal is delayed with respect to the replica generated by the receiver, as it travels ~20,000 km.
In order to find how much the satellite's signal is delayed, the receiver-replicated signal is delayed
until it falls into synchronization with the incoming signal (it is achieved at the point of maximum
correlation between the incoming PRN code and the receiver-generated replica). The amount by
which the receiver's version of the signal is delayed is equal to the travel time of the satellite's ver-
sion (Figure 9.8). The travel time, ∆t (~0.06 s), is converted to a range measurement by multiplying
it by the speed of light, c.
