Precise Orbit Determination of Global Navigation Satellite System of ...

Chapter 2 Observations of Orbit Determination
CHAPTER 2 OBSERVATIONS OF ORBIT DETERMINATION
The basic observations of orbit determination are ranges, range rates (Doppler), carrier-phases, laser ranging, etc.
According to the applications, these observations may be used for one-way or two-way systems. In this chapter,
the basic observations of orbit determination, the possible error budgets, the error models related to the receivers
and the advantages and disadvantages based on current satellite navigation systems, GPS/GLONASS are
discussed.
2.1 One-Way System
In a one-way system the signal transmitted from satellite is received by the ground tracking stations or the signal
transmitted from ground tracking stations is received by satellites. The received signal is then processed for orbit
determination. In a typical one-way system, the measurement is done by comparing a clock time at the
transmitter antenna with a clock time at the receiver antenna. The travel time of the signal is scaled into a range
measurement using signal propagation velocity. All microwave observations mentioned above can be used in a
one-way system.
2.1.1 Range
2.1.1.1 Basic Observation
S(t 2 )
S 1
Figure 2-1 One-way Range Measurement
3
r(t 1 )
S(t 1 )
As shown in Figure 2-1, assuming a clock time at the receiver antenna is t 2 , and a clock time at the transmitting
antenna is t1 , the one-way range measurement S1 can be expressed by
L = S1
= c(
t2
− t1)
+ ε
(2-1)
where
S1 the geometrical distance between the satellite and ground tracking station
c speed of light in vacuum
ε measurement noises such as ionospheric and tropospheric errors, multipath effect
satellite and receiver errors, and random noises
( t1)
r satellite geocenter position vector at t 1