Bernese GPS Software Version 5.0 - Bernese GNSS Software

6.6 Screening of Post-Fit Residuals
“RMS threshold level for a bad solution” only the station with the biggest total RMS error will
be marked as “bad”. The residual screening has to be repeated after removing the station.
The “bad” stations may be listed in a file allowing to delete the corresponding observation
files. If you have detected and removed bad stations you should recompute the residual files
(program GPSEST) and generate a new edit information file (program RESRMS) before
marking the observations with the program SATMRK. If you are processing a network
of baselines you have to rebuild the entire network (program SNGDIF) after deleting the
observation files of the bad station. The new baselines have, of course, to be preprocessed
again (program MAUPRP) before the residuals may be recomputed.
Bad Satellite Detection
You can download the file indicating satellite problems from the anonymous ftp account
of AIUB (http://www.aiub.unibe.ch/download/BSWUSER50/GEN/SAT_yyyy.CRX, where
yyyy is the four digit year). This file is updated every time when a new satellite problem
appears (satellite maneuvers, bad data,...) in the routine processing for the IGS at CODE.
Observations of misbehaving satellites are rejected by the program RXOBV3 in your processing
if you use this file. It is, therefore, not necessary for you to repeat the detection
procedure for misbehaving satellites.
Nevertheless, the description of the algorithm is given here:
(1) The CODSPP extraction (program CODXTR, see Section 6.3.4) and the arc split summary
(program DEFXTR, see Section 5.4.2) may contain hints for a repositioning of a
satellite. If at least one of these files shows an indication of a repositioning a maneuver
is postulated for the corresponding satellites.
(2) Satellites for which a maneuver is postulated but which show no abnormal behavior
with respect to the mean RMS in the bottom line of the RESRMS-residual summary
(option “Maximum ratio of satellite RMS to overall RMS” in the section “OPTIONS FOR BAD
SATELLITE DETECTION”) are dropped from the maneuver list.
(3) Satellites without any observations in the RESRMS summary table are added to the
list of bad satellites. This can happen, e.g., when all observations of the satellite in all
contributing observation files are marked.
(4) The number of observations from all stations or baselines to each satellite are compared
in the first and in the second table of the RESRMS residual summary (before and
after the screening of post-fit residuals). A satellite for which a big amount of data
is removed is assumed to be “bad” (option “Maximal percentage of deleted data”). This
part is skipped if a maneuver hypothesis holds for at least one satellite because a
maneuvered satellite may affect the residuals of other satellites.
Note that for GLONASS a four times higher value is applied than for GPS because
of the lower total number of observations (see subroutine RCSATCHK.f90).
(5) The ratio of the overall RMS for one satellite w.r.t. the mean total RMS for all satellites
is computed. If this ratio exceeds the specified maximum ratio (option “Maximum ratio
of satellite RMS to overall RMS”), the satellite is assumed to be “bad”. Two different
threshold ratios are used depending on whether satellites with a maneuver hypothesis
were identified or not.
Bernese GPS Software Version 5.0 Page 135