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Appendix A. Required external files

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This section briefly introduces the external files that need to be downloaded. For more information on the relevant files, please refer to the official website of IGS (https://igs.org/), the official website of IERS (IERS), etc.

A.1 Precise products

Satellite orbit products

The precise ephemeris product gives the orbit information of GNSS satellites at certain time intervals, including satellite coordinates, satellite clock errors and optionally motion velocity, coordinate standard deviation and satellite clock errors standard deviation. The current standard format is SP3 (Standard Product 3), including SP3-a, SP3-c and SP3-d. A brief description of SP3-d is given below, and the specific file format can be found at sp3d.pdf (igs.org).

  1. File header

    • The first line starts with “#a”, “#c” or “#d”, indicating the SP3 file type; the third character is “P” or “V”, marking the position or speed; the penultimate data is the reference frame. It should be noted that PRIDE PPP-AR cannot recognize the "# a" version of sp3 files;
    • The second line, beginning with “##”, records the GPS week for the corresponding day, the seconds of week, the sampling interval, the integer part and the fractional part of the MJD.

  2. Data blocks

    • The line starting with “*” marks the beginning of the epoch, followed by the corresponding epoch time;

    • The first character of the data line is "P" or "V", followed by the PRN of the satellite;

    • If the first letter is "P", the XYZ coordinates and clock deviation of the satellite will be recorded;

    • If the first letter is "V", the change rate of satellite XYZ velocity and clock deviation is recorded;

    • The end-of-file marker is "EOF".

image75

Figure A-1 Example of a SP3-d file

Clock difference products

The satellite clock difference product records the correction of the satellite time relative to the standard time. The latest file format is currently clock RINEX 3.04. A brief description of the corresponding format is given below, and the specific file format can be found at https://files.igs.org/pub/data/format/rinex_clock304.txt.

  1. File header

    • The comment “TIME SYSTEM ID” records the time system used;
    • The comment “SYS / DCBS APPLIED” records the input bias-SINEX file;
    • The comment “SYS / PCVS APPLIED” records the input ANTEX file;
    • The comment “LEAP SECONDS” records the value of the leap seconds;
    • The comment “SOLN STA NAME / NUM” records the station/receiver name, station/receiver identifier number and geocentric XYZ station coordinates.

  2. Data blocks

    • Column 1: Data type: "AS" represents satellite clock difference; "AR" represents the receiver clock difference (usually is the station);

    • Column 2: The name of the satellite or station: "AS" means satellite PRN; "AR" represents the name of the station;

    • Column 3-8: The epoch of the data occupies six columns (yyyy mm dd hh MM ss);

    • Column 9: The number of clock difference data in this line (usually 1 or 2. If is 1, there will be only clock difference; if is 2, there will be add clock difference standard deviation);

    • Column 10: Clock difference (unit: s);

    • Column 11: Optional, when the value in the ninth column is 2, it represents the standard deviation of clock deviation (unit: s).

image76

Figure A-2 Example of a clock RINEX 3.04 file

Earth Rotation Parameter

When fixing the satellite orbit, ERP parameters need to be considered for data processing under the inertial reference frames. ERP files record the Earth rotation parameters, including polar position and UT1-UTC, etc. The current version is version 2. A brief description of the corresponding format is given below, and the specific file format can be found at [IGSMAIL-1943] New IGS ERP Format (version 2).

  • MJD: modified Julian day
  • Xpole and Ypole: pole coordinates
  • UT1-UTC: Difference between UT1 (Universal Time) and UTC (Universal Time Coordinate)
  • LOD: Length of day

image77

Figure A-3 Example of an ERP file

Code/Phase bias

The current version of the bias file is Bias-SINEX V1.00. The absolute bias OSB (Observable-specific Signal Bias) of the original code/phase observations is recorded in the PRIDE PPP-AR default product. A brief description of the corresponding format is given below, and the specific file format can be found at sinex_bias_100.dvi (igs.org).

  1. File header

    • The penultimate parameter in the first row is the bias model, with “A” denoting absolute bias and “R” denoting relative bias;

    • The comment “OBSERVATION_SAMPLING” records the sampling interval;

    • The comment “PARAMETER_SPACING” records the effective time span of the bias;

    • The comment “TIME_SYSTEM” records the time system used;

    • The comment “APC_MODEL” records the antenna correction model of the bias.

    image78

    Figure A-4 Example of a code/bias file header

  2. Data blocks

  • The column sequence of data blocks is bias type, space vehicle number (SVN) of the satellite, satellite PRN, observation data type, start and end time, unit, bias value and its standard deviation;

    Generally speaking, there are three types of bias, and the three bias values can be converted to each other according to the formula. It should be noted that PRIDE PPP-AR can only handle OSB type deviation files.

    • Differential Signal Bias (DSB)

    • Ionosphere-free Signal Bias (ISB)

    • Observable-specific Signal Bias (OSB)

    For observation types, it consists of three characters. The first character represents the type of observation value, usually C (code pseudo-range) or L (carrier phase); The second character is the frequency number, which has different label for different frequencies. The corresponding relationship between frequency and label can be seen in [Table 5-4](https://file+.vscode-resource.vscode-cdn.net/e%3A/bug/PRIDE-PPPAR-master/doc/PRIDE PPP-AR v3.0 manual-en-1222.md#_ref144899485); The third character is the observation attribute, mainly distinguished by channel (branch) or code type.

  • The file end flag is "%=ENDBIA"

    image79

    Figure A-5 Example of a code/phase bias file data blocks

Quaternions

The quaternions file records the quaternions associated with the satellite attitude, which can be converted into a rotation matrix for the transformed of the earth-fixed system to the satellite-fixed system. The current file version is ORBXEX 0.09 (ORBit EXchange format) and the corresponding brief format is described below.

  1. File header

    • The comment “TIME_SYSTEM” records time system, consistent with the satellite orbit/clock difference file
    • The comment “EPOCH_INTERVAL” records the sampling interval;
    • The comment “COORD_SYSTEM” records the ECEF (Earth Center Earth Fixed) frame involved in the transformation.

    image80

    Figure A-6 Example of a quaternions file header

  2. Data blocks

    The data blocks are marked by “+EPHEMERIS/DATA” and “-EPHEMERIS/DATA”.

    • The current epoch line is marked with "# #", followed by the corresponding epoch time and the number of satellites in that epoch;

    • The data row is marked with "ATT", followed by satellite PRN, number of data, and corresponding quaternion.

    image81

    Figure A-7 Example of a quaternions data blocks

IONEX maps

IONEX-Format (Ionosphere map Exchange format) is a global ionospheric product calculated daily by the IGS using observations from GNSS stations. It mainly provides a generic interface to IGS ionospheric products that supports the exchange of 2- or 3-dimensional TEC maps given in a geographic grid. A brief description of the corresponding format is given below, and the specific file format can be found at ionex1.pdf (igs.org).

  1. File header

    • The lines with the label “DESCRIPTION” give a brief description of the technique, model, etc.;
    • “INTERVAL” indicates the interval between the TEC maps, in seconds (integer);
    • “# OF MAPS IN FILE” indicates the total number of TEC/RMS/HGT maps;
    • “ELEVATION CUTOFF” indicates the minimum elevation angle in degrees;
    • “BASE RADIUS” indicates the mean earth radius or bottom of height grid (in km);
    • “HGT1 / HGT2 / DHGT” defines an equidistant grid in height;
    • “LAT1 / LAT2 / DLAT” defines an equidistant grid in latitude;
    • “LON1 / LON2 / DLON” defines an equidistant grid in longitude.

  2. Data blocks

    The data block of a single epoch is enclosed by “START OF TEC MPA” and “END OF TEC MAP”, “START OF RMS MAP” and “END OF RMS MAP”.

    • “EPOCH OF CURRENT MAP” indicates the epoch of current MAP (UT);

    • “LAT/LON1/LON2/DLON/H” record initializing a new TEC/RMS/HGT data block for latitude “LAT” (and height ‘H(GT)’), from “LON1” to “LON2”.

image82

Figure A-8 Example of an IONEX maps file

Grid-wise VMF1/VMF3

VMF1 and VMF3 are tropospheric mapping models developed by the Vienna University of Technology, Austria. VMF1/VMF3 value for arbitrary sites can be determined through interpolation from the grid-wise VMF1/VMF3 data. A brief description of the corresponding format is given below, and the specific file format can be found at VMF Data Server - Products (tuwien.ac.at).

  1. File header

    • The line where “! Epoch:” is located records the epoch corresponding to the file;

    • “! Range/resolution” indicates the latitude and longitude ranges and their respective increments;

  2. Data blocks

    • latitude (unit: °)

    • longitude (unit: °)

    • hydrostatic “a” coefficient

    • wet “a” coefficient

    • hydrostatic zenith delay (unit: m)

    • wet zenith delay (unit: m)

image83

Figure A-9. Example of a grid-wise VMF1 file

image84

Figure A-10 Example of a grid-wise VMF3 file

SINEX

The SINEX (Solution Independent Exchange format) file records the station positions and velocity. The SINEX file with “.snx” suffix records the station position/velocity, and the SINEX file with “.ssc” suffix records the station coordinates. What we need is the SOLUTION/ESTIMATE Block, enclosed by the “+SOLUTION/ESTIMATE Block” and the “-SOLUTION/ESTIMATE Block”. The brief format of this section is presented below, and the specific file format can be found at Microsoft Word - sinex_v202.doc (iers.org).

  • Index: Index of estimated parameters. Values from 1 to the number of parameters.
  • TYPE: Identification of the type of parameter.
  • CODE: Site code for which the parameter is estimated.
  • PT: Point Code for which the parameter is estimated.
  • SOLN: Solution ID at a Site/Point code for which the parameter is estimated.
  • REF_EPOCH_: Epoch at which the estimated parameter is valid.
  • UNIT: Units used for the estimates add sigmas.
  • S: Constraint applied to the parameter.
  • ___ESTIMATED_VALUE___: Estimated value of the parameter.
  • __STD_DEV__: Estimated standard deviation for the parameter.

image85

Figure A-11 Example of a SINEX file

A.2 Table files

leap.sec

The time difference between UTC and UT1 needs to be kept within 0.9s as specified, otherwise the adjustment will take the form of leap seconds. The leap seconds file required by the software can be downloaded at ftp://igs.gnsswhu.cn/pub/whu/phasebias/table/leap.sec. It records the MJD and its leap second value on the day before the leap second occurred. Note that the first line of the leap seconds file ends with a “*” sign to distinguish it from other files with the same naming format. In case of no internet access computing, the user needs to download the file beforehand and place it in the table directory specified in the configuration file.

image86

Figure A-12 Example of a leap.sec file

sat_parameters

The “sat_parameters” file is used to record the satellite parameters. A brief description of the corresponding file format is as follows.

  • PRN: PRN of the satellite;
  • SVN: SVN of the satellite;
  • LAUNCHED: Launch time of the satellite in the format of YYYYDDD:SSSSS;
  • DECOMMISSIONED: Decommission time of the satellite in the format of YYYYDDD:SSSSS;
  • COSPAR-ID: Committee on Space Research-ID;
  • MASS: Mass of the satellite in the unit of kg;
  • MAX_YAW: Maximum speed of satellite rotation at the beginning of design
  • FID: The frequency ID of the satellite;
  • BLOCK-TYPE: Block type of the satellite;

image87

Figure A-13 Example of the sat_parameters file

ANTEX

The ANTEX (The Antenna Exchange Format) file is used to record the PCO/PCV at the satellite and station ends, which is stored in the “igsXX.atx” file, consistent with the current igsXX reference frame. The current version of the ANTEX file is Version 1.4. The brief description of the corresponding file format is as follows, and the specific format of the file can be viewed at https://files.igs.org/pub/data/format/antex14.txt.

  1. File header

    • “ANTEX VERSION /SYST” denotes file version and satellite systems included in the file
    • “PCV TYPE / REFANT” denotes the phase center variation type, ‘A’: absolute values, ‘R’: relative values;

  2. Data blocks

    The data block contains satellite antennas and receiver antennas, all organized in a hierarchical sorting way, single data block enclosed by “START OF ANTENNA” and “END OF ANTENNA”. Satellite antenna part: first sorted according to the satellite system, then sorted according to satellite code “sNN”, and finally sorted according to “VALID FROM”.

    • “TYPE / SERIAL NO” denotes the antenna type, satellite PRN, satellite SVN and cosplay-id;

    • “DAZI” denotes increment of the azimuth, “0.0” denotes non-azimuth-dependent phase center variations;

    • “ZEN1 / ZEN2 / DZEN” denotes the zenith distance “ZEN1” to “ZEN2” with increment “DZEN”;

    • “VALID FROM” and “VALID FROM” represents the start of validity period and end of validity period in GPS time, respectively;

    • “START OF FREQUENCY” and “END OF FREQUENCY” indicate the start and end of a new frequency section, respectively;

    • “NORTH / EAST / UP” denotes the mean antenna phase center relative to the center of mass of the satellite in X-, Y- and Z-direction (unit: mm);

    • The flag “NOAZI” denotes the non-azimuth-dependent PCV values, the PCV values from “ZEN1” to “ZEN2” were subsequently recorded.

image88

Figure A-14 Example of the satellite section of an ANTEX file

Receiver antennas part: first sorted according to antenna type, then sorted according to receiver radome code, and finally sorted according to the “SERIAL NO”.

  • “TYPE / SERIAL NO” denotes the antenna type and serial number;
  • “NORTH / EAST / UP” denotes the mean antenna phase center relative to the antenna reference point (ARP). North, east and up component (in millimeters);
  • IF “DAZI” > 0.0, the PCV value corresponding to the azimuth angle in increments of “DAZI” is recorded after the line where “NOAZI” is located.

image89

Figure A-15 Example of the receiver section of an ANTEX file

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