P. Heroux and J. Kouba 

Title
A Simple GPS Precise Point Positioning Interface Using IGS Orbit =
Products

Abstract
The International GPS Service (IGS) has provided orbit/clock products =
to the
GPS community with increased precision and timeliness.  A number of GPS
users interested in geodetic positioning have adopted the IGS precise =
orbits
to benefit from the stability of its reference frame and achieve =
centimetre
or better positioning accuracy. Currently, precise positioning is =
usually
achieved by operating in relative positioning mode with respect to one =
or
multiple reference stations while processing double-difference carrier =
phase
observations using a baseline or network estimation approach.   This =
mode of
processing has received widespread acceptance but continues to be =
hindered
by the requirement to include data from at least one, often distant,
reference station. Furthermore, the differencing approach does not =
allow any
useful clock solutions and results only in relative parameter =
estimates.
This poster describes a simple post-processing approach that uses IGS
precise orbit/clock products with dual-frequency pseudorange and =
carrier
phase observations from a single GPS receiver, to estimate station
coordinates and the related tropospheric and clock parameters. Results =
show
that global centimetre positioning precision is achieved, directly in =
ITRF,
when using orbits/clock solutions from different IGS Analysis Centres =
(ACs)
and the IGS combined products.  The point positioning results also =
reveal
the existence of apparent geocenter offsets between orbit products from
different ACs.  Furthermore, station tropospheric zenith path delays =
with
centimetre precision and GPS receiver clock estimates precise to .3
nanoseconds can also be obtained using this simple technique.=20
The single point positioning mode proposed here forms an ideal user
interface to the IGS orbit/clock products since it takes advantage of =
the
satellite clocks available with the coordinates in the IGS precise =
orbit
products.  Models accounting for centimetre variations in the satellite =
to
user range are implemented in a program that has a simple user =
interface and
executes within a few minutes using a personal computer.  This poster
summarises the approach, describes the adjustment procedure, specifies =
the
models implemented and presents initial results obtained with  this =
precise
point positioning interface.
Authors
Pierre H=E9roux and Jan Kouba