Technical description of dgf2018a.snx
          -------------------------------------

 1.  Purpose: Datum-free VLBI session normal equation files in SINEX 2.02 
     format, including station/source coordinates and EOP.

 2.  Analysis Center: Deutsches Geodaetisches Forschungsinstitut (DGFI-TUM), 
     Technische Universitaet Muenchen, Munich, Germany

 3.  Estimated parameters:

     a. Celestial frame: Yes

     b. Terrestrial frame: Yes

     c. Earth orientation: Pole coordinates and their first derivatives, 
        UT1-UTC and LOD, dX, dY, each valid for the duration of the 
        session (normally 24 h), reference epoch is mid of session

     d. Zenith troposphere (per station): 
        continuous piece-wise linear function (1 hour)  
        rate constraint 66.0 ps/h

     e. Troposphere gradient (per station): 
        discontinuous piece-wise linear function (24 hours)
        offset constraint 2.5 ps
        rate constraint 5.0 ps/h

     f. Station clocks (per station): Quadratic function per session plus
        a continuous piece-wise linear function (1 hour) 
        offset constraint 66.0 ps 
        rate constraint 135.0 ps/h
        (clock jumps estimated additionally)
 
 4.  Celestial reference frame:

     a. A priori source positions: ICRF2

     b. Source positions adjusted in solution: Yes (>3 observations)

 5   Terrestrial reference frame:

     a. A priori station positions: ITRF2014

     b. A priori station velocities: ITRF2014

     c. Axis offsets: taken from official IVS-table
        http://vlbi.geod.uni-bonn.de/Analysis/Thermal/antenna-info.txt

     d. Reference epoch: session epoch

 6.  Earth orientation:

     a. A priori precession/nutation model: IAU2006A

     b. A priori x and y pole coordinates and rates, UT1-UTC and rate: 
        IERS EOP 14 C04, cubic window interpolation 

     c. A priori short period (~daily and subdaily) tidal variations in 
        x, y, dUT1: IERS Conventions 2010

     d. EOP estimation: Pole coordinates and rates, UT1-UTC and rate (UT1dot), 
        dX, dY, each valid for the duration of the session 
        (normally 24 h), reference epoch is mid of session (see the
        SOLUTION/APRIORI block)

 7.  A priori geophysical models:

     a. Troposphere: hydrostatic component from surface pressure (in 
        general as reported in the NGS files) mapped with the VMF1
        dry mapping function, wet delay is estimated with the VMF1 
        wet mapping function. A priori values for the gradients are 
        from TU Wien (Boehm & Schuh, 2007) since 2005.0 and from GSFC
        (MacMillan, 1995, and MacMillan & Ma, 1997) before 2005.

     b. Solid Earth tide: IERS Conventions 2010

     c. Tidal ocean loading: FES2004

     d. Pole Tide: IERS Conventions 2010

     e. Atmosphere loading: Petrov & Boy (2003) 
        https://lacerta.gsfc.nasa.gov/aplo_eph/

     f. Thermal deformation: according to IVS conventions 
        http://vlbi.geod.uni-bonn.de/Analysis/Thermal/antenna-info.txt

 8.  Data type: Group delays

 9. Data editing: 5-degree elevation cut-off

 10. Data weighting: Only observations with a zero quality flag in NGS 
     cards are used. All observations are subject to an outlier test 
     (data snooping).

 11. Software: DOGS-RI 1.0

 12. Further information:
     The SINEX 2.02 files include datum-free normal equations only, no 
     solution. None of the station/source position parameters or EOP reported 
     in this file are subject to any constraints.