Global Positioning System Reference
In-Depth Information
CHAPTER 7
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
[Fir
PROCESSING PSEUDORANGES
A ND CARRIER PHASES
[22
Lin
0.0
——
Nor
PgE
In keeping with the objectives of this topic, this chapter does not contain the depth
required to determine global positioning system (GPS) orbits or orbits of near-earth
satellites. Rather, the position is taken that precise GPS satellite ephemerides will
be available from the International GPS Service (IGS) and participating agencies
and individuals who will continue to fine-tune their models as part of their research
agenda. Therefore, the first section deals with the IGS and its products.
A separate section is devoted to antennas. Because of the increasing popularity of
precise point positioning (PPP), material is included on the phase windup correction
that results from the fact that the GPS satellite transmissions are right circularly
polarized. The separation between the center of the satellite antenna and the satellite's
center of mass must be properly dealt with in precise PPP application and respective
corrections must be applied. The two types of corrections are little known among
users performing relative positioning over short distances, because they cancel. All
users however, must be concerned with receiver antenna phase center offsets and
variations, and, certainly, signal multipath. These phenomena are treated in some
detail.
The various GPS positioning techniques are subdivided into geometry-free so-
lutions, point positioning (navigation solution), precise point positioning, real-time
precise point positioning, relative positioning (differential positioning), and real-time
relative positioning (real-time kinematic positioning [RTK] and network-aided RTK).
PPP, in either the static or kinematic mode, is becoming increasingly important be-
cause of the availability of very precise postprocessed satellite ephemerides within a
short delay time or even predicted precise ephemerides, and the discontinuation of se-
lective availability (SA). PPP becomes even more attractive because of computational
services that conveniently are available over the Internet. An example is the service
[22
228
 
Search WWH ::




Custom Search