DORIS data format description

Format change: January 2004

An improved tropospheric delay computation algorithm is introduced in the data preprocessing. See DORISMail Slight change (Jan 2004) Nr 301 

 
Starting arc/cycle:     JASON-1         cycle  73  ja1data073...
                        TOPEX/POSEIDON  cycle 417  topdata417...
                        ENVISAT         arc    76  en1data076...
                        SPOT-5          arc    65  sp5data065...
                        SPOT-4          arc   251  sp4data251... 
                        SPOT-2          arc   498  sp2data498...

Format change: January 2002

Data are delivered under either of two versions of the file content, depending of the date of the observations. The change of format is not reflected in the data filenames.

Starting dates for the adoption of the 2.1 format 
 
      JASON-1         cycle   1  (15-24 Jan 2002)  ja1data001...
      TOPEX/POSEIDON  cycle 344  (15-24 Jan 2002)  topdata344...
      ENVISAT         arc     7                    en1data001...
      SPOT-5          arc     1                    sp5data001...
      SPOT-4          arc   168  (11-20 Jan 2002)  sp4data168... 
      SPOT-2          arc   413  (11-17 Jan 2002)  sp2data413...

  • The 1.0 format that was first used to distribute the data is acceptable only for the pre-Jason receivers. Times t1 and t2 (start and end of observations) are given in TAI. The Doppler count is converted from cycles to mm/s based on frequency values that are the best estimates (polynomial model for the onboard Ultra Stable Oscillator (USO), pass by pass solutions for ground beacons) derived in the Precise orbit determination (POD) process.

  • The 2.1 format is a slight modification of the 1.0 format, with the following characteristics. Times t1 and t2 are in TAI. The Doppler count is converted from cycles to mm/s based on the timing polynomial for the onboard frequency and nominal values for the ground beacons. The 2.1 format better fits the analysts needs, in particular in the context on multi-satellite solutions.

    The change from formats 1.0 to 2.1 may be summarized as follows.

  • Columns 46-56: Range rate is computed with
    f(bea)= nominal (instead of best estimate) beacon frequency
  • Column 90: Channel indicator
  • Users should also check column 35: preprocessing indicator.
    With format 1.0, CNES only measurements considered to be good were delivered (value = 0).
    With format 2.1 edited measurements may also be delivered (value=1 for preprocessing, value=2 for postprocessing)

    More on the change in DORISMail No 0197