BERNese's data processing method
Transfer from: http: //blog.sina.com.cn/s/blog_5d2058ca010126gc.html author: cub
BERN's data processing method. Basically it can be divided into the following steps:
1. Preparation for processing data
This step includes preparing the observation file, ephemeris file, and updating the table file required for data processing, and then converting the RINEX format data into the Bernese binary format file, in order to accelerate the data reading rate.
The files in RINEX format are observation files (ssssdddf.yyo), navigation files (ssssdddf.yyN, ssssdddf.yyG) and meteorological files (ssssdddf.yyM). Observation files are converted into BERNESE format in the following four formats, which are:
* .PZH (phase non-difference header file)
* .PZO (phase non-difference observation file)
* .CZH (code non-difference header file)
* .CZO ( Code non-difference observation file)
The conversion of navigation file and weather file is similar to this. In the process of converting the original file from RINEX format to BERNSE format, sometimes an error occurs and the receiver type is considered to be Phas_igs. The O1 file does not match, resulting in unsuccessful conversion. The main problem is that there may be illegal characters in the original file in RINEX format. This problem can usually be checked by checking the original file for illegal characters or standardized with the data management software teqc, which can be downloaded from www.unavco.ucar.edu.
Before running the software, you must first prepare the necessary files, including:
(1) Original files (%% o, %% n, %% m) have original observation files, original navigation files, and original meteorological files. It is mainly the original observation file;
(2) The Datum File (DATUM) includes the current datum model. Unless new ground reference plane model is added, there is generally no need to change;
(3) Phase center correction table (PHASE__IGS.01) includes most commonly used antennas and receivers and their parameters;
(4) Earth gravity field model (JGM3., GEMq3.) GEMq3. Is used manually, and JGM3. Is used for BPE calculation, no need to change;
(5) Polar deviation coefficient file (POLOFF.) Generally does not need to be changed;
(6) Satellite parameters (SATELLIT.EX1) should be changed to SATELLIT.TTT;
(7) Constants (CONST.) Including speed of light, L1, L2 frequency, earth radius , Normal light pressure acceleration, etc .; generally not changed;
(8) Receiver information file (RECEIVER.) Mainly includes receiver type, single and dual frequency conditions, observation code and receiver phase center correction, etc., if there is a new receiver The type can be added in the prescribed format in this file;
(9) Earth rotation parameter information file (C04- $ JJ2.ERP) $ JJ2 is a specific year, we changed it to 2002, etc., and it should be downloaded in accordance with the observation time Relevant documents;
(10) GPS jumping seconds (GPSUTC) GPS jumping seconds;
(11) Satellite problem files (SAT- $ JJ2.CRX) including bad satellites and their observations. $ JJ2 is a specific year, we will change it to 2002 and other forms of the year;
(12) Station problem file (STACRUX.) The antenna height of the station, the center correction and other record files of the situation.
Among the above files, (2)-(12) can be downloaded from ftp://ftp.unibe.ch/aiub/BSWUSER/, under normal circumstances, (2), (4), (5), (7) , (8), (10), (12) do not need to be changed, (3), (6), (9), (11) should be updated frequently, in addition, the antenna height table file, antenna and receiver conversion must also be prepared Table files, initial coordinate files, and precision ephemeris files. Among them, the precision ephemeris file will be changed from the orbit format sp3 file downloaded from IGS to a PRE file (sp3 file format has been updated to sp3-c on September 5, 2002 Format), can also be downloaded from the menu Menu2.0.21, such as: igs10765.sp3 changed to IGS10765.PRE (all letters in the file name in the BERNESE42 software must be capitalized), antenna height table file, antenna and receiver conversion table file ( It is worth noting that in the process of generating the antenna and receiver conversion table, the receiver and antenna types in the file header in the observation file that has been converted to the RINEX format should be capitalized, otherwise it will be wrong), the initial coordinate file must be manually generated, and attention must be paid to The format of coordinate input in the initial coordinate file, otherwise it is easy to make mistakes, and the update of data or files can be done through the website ftp: //ftp.unibe, ch / aiub / BSWUSER , ftp: //ftp.unibe,ch/aiub/CODE or www.aiub.unibe.ch/download.
2. Standardization of satellite orbits
Satellite ephemeris can choose precise ephemeris or broadcast ephemeris. Bernese software has two main programs in the track part, the first program is PRET. AB, whose main job is to convert the precise ephemeris from the geocentric fixed coordinate frame to the inertial coordinate frame, and the program also extracts the satellite clock difference. The second program is ORBGEN, whose job is to generate standard tracks from track table files. A standard track file is usually generated for each period (usually one day). If a precise ephemeris is used, the root mean square error (RMS) of the standard orbit generated by ORBGEN is generally less than 3 cm. Another important function of ORBGEN is to integrate the resolved orbital elements to produce precise orbitals.
Third, calculate the receiver clock correction
The program for calculating the receiver clock correction is CODSPP. The calculated clock corrections are stored in the phase and pseudorange observation files. The posterior root mean square error value will be provided in the output file of this program.
4. Form a baseline document
SNGDIF forms an independent baseline single difference file in the entire processing network according to the selected criteria. Generally, the maximum observation value criterion (OBSMAX) is selected, that is, the common observation between the two stations constitutes the baseline for the most. The baseline can also be defined manually or by other standards.
V. Preprocessing of phase observations
For high-precision positioning, clean phase observations are a prerequisite. We know that there are multiple data preprocessing methods in the Bernese software. But the core program for preprocessing phase observations is MAUPRP (Manual and AUtomatic PRe-Processing). It can handle both non-difference data and single-difference data.
6. Parameter estimation
There are two main programs for parameter estimation in Bernese, one is GP. SEST, based on the original observations to solve the parameters; the other is ADDNEQ2 (version 4.2 is ADDNEQ), based on pseudo observations (normal equations or SINEX files) to solve the parameters. GPSEST combines the pre-processed phase observations into second-difference observations to solve the coordinate parameters. In the specific solution, there are many different settings and techniques according to different situations, especially for the ambiguity parameters and epoch parameters (dynamic coordinates and receiver clock difference). In general, QIF (Quasi-Ionosphere-Free) method is used to solve the ambiguity, and the correlation of the baseline is ignored, and the method of solving each baseline is used. The epoch parameters are generally pre-eliminated and then iteratively solved at the normal equation level. It is worth emphasizing that observation preprocessing and parameter estimation are an iterative process. Clean observations can lead to more accurate parameter solutions, which in turn help to obtain cleaner observations.
Seven, multi-time comprehensive solution
This part of the program is ADDNEQ 2, and all the baseline solutions obtained in step 6) are used as pseudo observations and then adjusted to obtain a more accurate parameter solution, or to invert some other parameters, such as station speed and earth rotation Parameters etc.
The steps are as follows:
1) Project installation
2) Copy or download GEN related files, ATM, STA folders to the project folder
3) Check meteorological files *. ATM, GEN general files (CONST. (All constants used by this software)-DATUM. (Projection plane definition)-RECEIVER. (Receiver information)-PHAS COD. I01 (phase center correction table) -RADOME CODES-SATALLIT.I01 (satellite information file) -SAT $ Y + 0.CRX (satellite problem file) -GPSUTC. (Jump second file issued by IERS) -IAU2000.NUT (chapter model parameter file) -IERS2000 .SUB (half-day polar shift model parameter) -POLOFF. (Polar deviation coefficient) -JGM3. (Earth gravity field model) -CSRC.TID (tide parameter) -SINEX.TRO-SINXE.PPP-SINEX.RNX2SNX-IONEX.- IONEX.PPP), orbit file * .PRE and earth rotation parameter file (polar shift information file is provided once a week) * .IEP
4) Rinex files (RINEX files of the clock are located in the OUT subdirectory, and these files are stored in the ORB subdirectory together with IGS orbit data and ERP data. These files contain station and satellite clock clock corrections. The sampling interval for clock corrections is 5 minutes)
5) Station file * .STA (under the ITRF2000 reference framework, using the data provided by the IGS center, you can get the a priori coordinates of the station, the a priori coordinates are stored in the file IGS 00.CRD. It uses a batch PPP program The station coordinates in the example are generated according to the 143th day of 2002. It contains the coordinates of all IGS core stations (copied from the IGS 00 R.CRD file-IGS 2000 reference framework at that time was ITRF2000), and the coordinates of the remaining stations The a priori coordinates are the results of the batch program PPP calculation. The coordinate epoch is January 01, 2000. The velocity field file corresponding to the station coordinate file is IGS 00.VEL, and the core is included in the IGS 00.VEL file Station speed (copied from file IGS 00 R.VEL), the speed of the core station is calculated by the NNR-NUVEL1 A speed of other stations. The file Example.PLD provides that the stations are distributed in different sectors The above situation. The file IGS 00. FIX contains a list of all IGS core stations. When estimating the station coordinates, it is very useful to define the earth coordinate system reference. Confirm the station information in the data processed by Bernese software is correct (Station name, receiver type, Antenna type, antenna height, etc.), the file Example.STA is used to verify the header information of the RINEX file. The reason for using this file is: in practice, some antenna heights or receiver / antenna will appear in the RINEX file The type is incorrect. The antenna height based on the reference points of different antennas may not be measured correctly. Similarly, the name of the station name in the RINEX file may not be the same as the name of the station we want to deal with. The receiver antenna type must be consistent with the file The definitions of PHASCOD.I01 match, the reason is that the offset and change of the receiver antenna phase center will be used. The receiver type must be defined in the receiver.file, and the DCB should be correctly applied in the file for correction. The last file mentioned in the section is Example.BLQ. It provides and loads the ocean tidal coefficient of the station to be processed. It is generally used in the final operation program (GPSEST) for parameter estimation)
6) The extrapolation method generates a priori coordinates * .CRD (Before obtaining the a priori coordinates through the PPP program in the batch processing program BPE, the reference epoch should be set to January 1, 2000)
7) Import RINEX data conversion
8) Prepare the polar shift information file.
In the ORB subdirectory, a set of fixed earth orientation information including the precision orbit file (PRE) is provided. However, the precision track files are published by the IGS Center from the final data series, and the update frequency is once a week, which can be used as the track file EOPs used within the same week. These information files defined in the IERS / IGS standard format (file extension in Bernese * .IEP) must be converted to information files defined in Bernese internal EOP format (file extension in Bernese * .ERP) ).
9) Generate a tabular orbit file (TAB) and satellite clock file (CLK). If there is no broadcast ephemeris orbit file, the clock file will be called when the running program CODSPP runs
10) Generate standard orbit files *. STD
contains important information about the RMS (root mean square) error of each satellite in the output file, if the precise orbit data used is consistent with the information in the EOP file (true RMS (mean square Root) The error depends on the quality of the precision orbit file and the polar shift file. The polar shift file realizes the conversion between the ITRF reference frame and the ICRF reference frame; there is also the orbit model option selected in the running program ORBGEN). The RMS (root mean square) error should not be greater than 1 to 2 cm. Comparing the RMS (root mean square) error after the second iteration is completed and after the second iteration is completed, it can be concluded that the result after 2 iterations is sufficient It is now possible to generate precise standard orbit data for GNSS satellites.
11) The receiver clock synchronization calculation (CODSPP)
in the output file, the most important information is: CLOCK OFFSETS STORED IN CODE + PHASE OBSERVATION FILES (the clock difference value stored in the code + phase observation value file), it will display The receiver clock difference value δk calculated by running the program CODSPP is simultaneously saved in the code and phase observation value files. Through this step of calculation, the code observation file is no longer used during the further processing of the sample data. In the output file after the end of the program CODSPP, you can check (each processed non-difference (zero difference) file) posteriori root mean square error (posteriori RMS error).
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PS：
During the processing of GPS data, Bernese will encounter all kinds of unexpected errors and warnings. Even if you have been using it for several years, you will remember every step of the operation. It is difficult to grasp the essence.
