About The Atmospheric Effects; About Orbit And Orbit Perturbation Parameters And Errors - R&S SMW-K44 User Manual

Satellite Navigation

12.1.1 About the Atmospheric Effects

When traveling thought the atmosphere, the satellite signal experiences changes it
speed and direction. While the increased travel time due to signal refraction is insignifi-
cant, the variation in the signal propagation speed causes pseudorange measurement
errors.
Tropospheric effects
The troposphere is the lower atmosphere layer that comprises rain, snow, clouds, etc.
and affects the GNSS signals propagation. The GNSS signals experience a variable
path delay, caused mainly by the dry atmosphere. The severance of this delay
depends on the pressure, humidity, temperature and the location of the receiver and
the satellite.
Ionospheric effects
The severity of the ionospheric effect depends geographical location of the receiver,
the hour of day and the solar activity.
The ionospheric effects are frequency-dependent and can be counteracted by fre-
quency measurements. For single frequency receivers, the navigation message con-
tains a set of parameters that describe an ionospheric prediction model with the goal to
remove the ionospheric effect.
Tropospheric and ionospheric models
The R&S SMW simulates atmospheric effects based on two models, a tropospheric
and an ionospheric one. These models define the ionospheric and tropospheric models
used to simulate the channel between the satellite and receiver. You can enable and
set each of them independently. The selected model applies for all satellites, irrespec-
tively to the GNSS system they belong to.
The provided models differ in terms of complexity. The ionospheric models also
assume different approximation of ionospheric effects. For information on the suppor-
ted models, see:
●
"Tropospheric Model"
●
"Ionospheric Model"
Ionospheric model vs. ionospheric parameters in the navigation message
The ionospheric model defines the satellite to receiver channel, whereas the iono-
spheric navigation parameters define what the satellites are transmitting (broadcasting)
as ionospheric correction parameters.

12.1.2 About Orbit and Orbit Perturbation Parameters and Errors

The different GNSS systems use specific approach to describe the satellite's orbit and
orbit perturbations.
The orbit description in the GPS, Galileo, BeiDou and QZSS systems is based on the
first approximation of 16 Keplerian parameters. The navigation message of a GPS sat-
User Manual 1178.6379.02 ─ 01
Perturbations and Errors Simulation
on page 108
on page 108
About the Errors Sources
102