Bernese GNSS Software, Version 5.2 is a high-quality geodetic software package for the post- processing mode (Dach et al., 2007). Bernese software is widely used for geodetic networks estimation in many aspects. In addition, it has the potential to process the GNSS data for the static and kinematic applications. Moreover, it processes the measurement data in double-difference (Differential GNSS estimation) and zero-difference (PPP solution estimation) (Dach et al., 2007). Complete documentation of the software can be obtained from the official website under
(http://www.bernese.unibe.ch/). Dach et al. (2007) provided the user manual, and Dach and Walser
(2015) showed a course tutorial including processing examples, introductory course and a terminal session; this tutorial is always updated. The complete descriptions for the processing procedure are illustrated in Appendix A.
Figure 5.2 is a flow chart depicting a brief explanation about the processing using Bernese GNSS software. The processing in the case of the kinematic PPP technique is obtained using the automatic script (Bernese Protocol Engine (BPE)). The related processing steps for the PPP solution are illustrated in the following points:
The related processing data, e.g. satellite orbits, clocks and earth rotation parameters, are downloaded from the CODE ftp server.
The orbit tools, which are used to prepare the earth orientation parameters, generate the satellite clock, and prepare the standard satellite orbits.
The pre-processing of the RINEX files, which are used to create observation statistics, smooth code and phase observation data from the outliers and cycle slips, is performed in addition to convert the observation data to a binary Bernese format.
The orbit and the binary observation data are inserted to the synchronization process for the receiver clock using the dual code combination. These clock errors are stored to the binary observation files; moreover, an a priori kinematic file is generated.
The parameter estimation for the zero-difference solution (PPP solution) is estimated using the main program GPSEST. In this case, the orbit data, observation data after receiver clock synchronization and the a priori kinematic file are inserted into the estimation. As described in Appendix 1, two loops from the GPSEST program are realized inside the software to get the final solution:
1. The first solution is aimed to generate a residual file for the data based on the L3 linear combination. Residuals are written as elevation dependent weighting of the observations. The solution is followed by residual statistics for estimation outliers (using program RESRMS). Then the residuals are screened. The satellite residuals with more than 6 mm for phase and 60 cm for code are marked as
56 Concept and Realization of Measurements
outliers (using program SATMRK). These outliers are eliminated afterwards from the next estimation.
2. The second solution is based on the cleaned observation.
The main programs of ADDNEQ, NUVELO, COOVEL and CRDMERGE aim to determine
the coordinate velocity and merge the different static solutions for the networks.
Download orbit data
POLUPD PRETAB ORBGEN Orbit tools Rinex measurement data RNXGRA RNXSMT RXOBV3 Preprocessing tools Clock Synchronization CODSPP & CODXTR
A priori kinematic file
CODE/IGS ftp server
Static Kinematic
Receiver Clock error stored to Obs. files GPSEST/RESRMS/SATMRK/ADDNEQ2 GPSXTR/RESCHK/HELMR1 Processing tools NUVELO/COOVEL/CRDMERGE Final Solution PPP kinematic file
Figure 5.2: General processing schedule for Bernese GNSS software in PPP technique
Turning now to the double-difference solution, it can be seen from Figure 5.3 that the processing procedure for the double-difference solution begins with the same pre-processing steps as for the PPP solution, Figure 5.2. What follows is a brief outline of the double-difference solution:
The baseline is created in Bernese software throughout (SNGDIF program), and this single difference is sorted into files;
Four loops using GPSEST program are performed for the main estimation of the parameters
as follow:
1. The main task of the first loop is to screen the satellite residuals using float solution (L3). The residuals are displayed (using REDISP program) and the statistical summary file is stored (with RESRMS program),
2. The second loop aims to estimate the tropospheric delay using float solution (L3) 3. The ambiguity resolution is resolved in the third loop using GPSEST program. The tropospheric delay, which is estimated in the second loop, is defined as a
57
known parameter. The estimated ambiguities for L1 & L2 are stored. The summary of the ambiguity resolution is generated by the GPSXTR program. 4. The final estimation of the coordinates can be accomplished through the fourth
loop, where the stored ambiguities are inserted in this case, and the a priori kinematic coordinate file from the CODSPP program is inserted as well.
Loop 4 Loop 3 Loop 2 Loop 1
Download orbit data
POLUPD PRETAB ORBGEN Orbit tools Rinex measurement data RNXGRA RNXSMT RXOBV3 Preprocessing tools Clock Synchronization CODSPP & CODXTR
A priori kinematic file
Pre-processing (Residual screening) GPSEST/REDISP/RESRMS
CODE/IGS ftp server
Form Baseline (SNGDIF)
Static Kinematic
Receiver Clock error stored to Obs. files
First solution (Tropospheric delay estimation) GPSEST
Satellite residuals
Tropospheric delay
Ambiguity resolution (Save estimated ambiguity for L1 & L2) GPSEST/GPSXTR
Store ambiguity
Final estimation (Final solution)
GPSEST/ADDNEQ/NUVLEO/COOVEL/CRDMERGE
Double-difference kinematic file
Figure 5.3: Bernese GNSS software flow chart for double-difference solution
As previously described, the processing using Bernese GNSS software is carried out for the double- difference solution step by step. In case of the PPP solution, an automated script (Bernese Protocol Engine (BPE)) is used in the estimation; this script may be adapted relative to each case study. The processing parameters for the computations in this thesis using Bernese software are illustrated in Table 5.1. The used satellite orbit and clock data are provided from CODE with different clock intervals related to the case study. Satellite and receiver phase centre offsets are considered using the IGS-ANTEX format (NGS, 2015, and CODE_FTP, 2015). The tropospheric correction is applied using two models (NIELL, GMF, and VMF1) for the hydrostatic and wet delay estimation. These models are applied related to the case study. Regarding ionospheric correction, the estimation of the PPP solution is based on the linear ionospheric-free combination. Moreover, high order ionospheric parameters are used to improve the estimation. For an accurate estimation, the ocean tidal loading
58 Concept and Realization of Measurements
correction is considered in the PPP estimation; the model parameters (of FES2004 model) are obtained through the website of Scherneck (2011). The atmosphere tidal loading is corrected by the Ray and Ponte model based on the IERS 2010 conventions (Ray and Ponte, 2003).
Table 5.1: Bernese software processing parameters for the thesis
DI ledoM
Reference System ITRF2008
Coordinate format Cartesian & Ellipsoidal
Satellite Orbits CODE/15 min
Satellite clocks CODE/05 s, CODE/30 s
Satellite phase centre offsets PCV.I08 (ANTEX format)
Receiver phase centre offsets PCV.I08 (ANTEX format)
Tropospheric model NIELL, GMF, VMF1
Ionosphere model Linear ionosphere free combination
Higher order parameters
GNSS System GPS
Observation data Both phase and code
Ocean tidal loading FES2004 model
Atmosphere tidal loading Ray and Ponte 2003 model
based on ITRS 2010
Cut off elevation angle 10°
Sampling rate 30 s/5 s/1 s