Bernese GPS Software Version 5.0 - Bernese GNSS Software

7. Parameter Estimation
are addressed with the DYX-directions in this panel but dependent on your setting
for the “ORBIT MODEL IDENTIFIER” (panel “ORBGEN 3.1: Options”) the dynamical parameters
are set up either in the DYX- (orbit model F) or in RSW-directions (radial,
along-track, out of plane, orbit model G).
(5) Start the screening of the phase data by using program MAUPRP in zero-difference
mode. Enable the “Kinematic coordinate estimation”. For the GNSS satellites a standard
orbit together with a consistent precise GNSS satellite clock file has to be specified in
panel “MAUPRP 1: Input Files”. Introduce the initial LEO orbit from processing step (4)
in panel “MAUPRP 1.2: LEO Processing”, “LEO standard orbit”. Adjust the options “A priori
coordinate/baseline vector sigmas” and “Sigma for L1/L2 observations” to the quality of your
LEO orbit. We refer to Section 6.5 for a detailed program description.
If an attitude file is available for the satellite, it should be selected in the field “LEO
attitude”.
(6) The screened phase observation files are used in GPSEST to improve LEO orbit parameters.
The radiation pressure file together with the corresponding standard orbit
(obtained in step (4)) has to be introduced for “Orbit partials” respective “Standard
orbit(s)” in the “LEO INPUT FILES” section of panel “GPSEST 1.2: Input Files 2”. In
panel “GPSEST 4: Datum Definition for Station Coordinates”, the coordinates (“Coordinates
fixed”) should be fixed for ALL stations. We recommend to pre-eliminate the “Ambiguities”
AS SOON AS POSSIBLE and the “Receiver clock offsets” EVERY EPOCH (panel
“GPSEST 5.1: Setup of Parameters and Pre-Elimination 1”). Make sure that the backsubstitution
of the receiver clock parameters is disabled (select no clock result file
and enable the printing option “Suppression of output concerning epoch parameters” in
“GPSEST 3.3: Extended Printing Options”). If you are interested in the receiver clock corrections
for the LEO you are not allowed to pre-eliminate any non-epoch parameter
(e.g., ambiguities).
With the activation of “GNSS or LEO orbit determination” in panel “GPSEST 5.2: Setup
of Parameters and Pre-Elimination 2” the panel “GPSEST 6.9.1: LEO Orbit Determination 1”
appears. It is recommended to improve all the orbital elements and the dynamical
parameters and, most importantly, to activate the option “ESTIMATION OF STOCHAS-
TIC PULSES”. The dynamical parameters are again addressed with the DYX-directions
in the panel but corresponding to ORBGEN it depends on the selection of the orbit
model whether the parameters are set up in DYX- or RSW-directions.
In panel “GPSEST 6.9.2: LEO Orbit Determination 2” it is necessary to specify the “Number
of parameter sets per day” (e.g., 96 means every 15 minutes), whereas stochastic pulse
parameters may be set up in up to three directions. The “Radial”, “Along track”, and
“Out of plane” directions are recommended for the LEOs (“A priori sigma” of 5.0D-6 m/s
is suitable). For the processing of one single LEO, it is not necessary to specify the
parameter setup with “SATELLITE-SPECIFIC PARAMETER SETUP”.
It is important for the subsequent update step with ORBGEN to write an orbital
element file with option “LEO orbital elements” in panel “GPSEST 2.2: Output Files 2”.
(7) The improved LEO orbital elements are introduced in the input field “Update standard
orbit” of the top panel of ORBGEN. The result is an improved standard orbit for the
LEO. Details on orbit determination are discussed in Section 15.3.
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