   Specifications of TROPO_PATH_DELAY Exchange format Version 1.1
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

   TROPO_PATH_DELAY format is for
1) providing a template for computation of slanted path delay in the
   neutral atmosphere as well as its partial derivatives in the direction
   of the symmetry axis of the neutral atmosphere and partial derivatives
   on directions of that axis, and

2) for distributing results of variations.

   A file in TROPO_PATH_DELAY format consists of records of variable length
in ASCII coding. The records are separated by a character with decimal
code 13. The records are grouped into sections. Sections follow
in this order:

1) Header record -- the first record should have a signature:
                    TROPO_PATH_DELAY  Format version of 2007.10.04

                    The header record allows to distinguish a valid
                    file in the TROPO_PATH_DELAY  format from files
                    in other formats.

2) E-records section
   E-record  has letter E in the first field. It specified the experiment
             name.

3) H-records section
   H-record  has letter H in the first field. It specified the secondary
             experiment name.

4) M-records section
   M-record  has letter M in the first field. The M record keeps the
             model identifier.

4) U-records section
   U-record  has letter U in the first field. The U instructs analysis
             software how to use the data. Analysis software may 
             override this recommendation.

5) S-records section
   S-record  has letter S in the first field. It defines a name
             and coordinates of each site. A site cannot be defined
             more than once.

6) O-records section
   O-record  has letter O in the first field. It defines
             circumstances of the observation: the time tag, site ID,
             azimuth and elevation in the local topocentric coordinate
             system surface atmospheric pressure and air temperature,
             slanted path delay and its partial derivatives.

7) Trailer record -- the last record is the same as the header record.

Records which start from # character are considered as comments.


Format of a U-record:

Field  1:1   A1    -- Record ID. Should be letter U (decimal code 85).
field  2:2   a1       delimiter: blanks.
Field  4:67  A64   -- a 64 characters long string with keywords separated
                      by blank. Recognized keywords:
                      ZEN   -- interpreted the field "slanted path delay" 
                               as zenith path delay and use it.
                      SLANT -- use slanted path delay
                      DERZ  -- use partial derivative with respect to the
                               zenith path delay
                      DERN  -- use partial derivative with respect to the 
                               tilt of the atmosphere symmetry axis in the
                               north direction.
                      DERE  -- use partial derivative with respect to the 
                               tilt of the atmosphere symmetry axis in the
                               east direction.
	              Example: STANT DERZ

Format of an S-record:
----------------------

Field  1:1   A1    -- Record ID. Should be letter S (decimal code 83).
field  2:2   a1       delimiter: blanks.
Field  4:11  A8    -- 8-letter long site identifier. May contain
                      any characters with decimal codes 32-255, but
                      blanks are allowed only at the end of the site
                      identifier. This site identifier should be unique
                      among S-records. This field should not
                      necessarily have a special meaning. Parsing
                      software should not try to interpret it.
field 12:13  a2       delimiter: blanks.
Field 14:26  F13.4 -- X site coordinate in a crust fixed reference
                      frame. Units: meters.
field 27:27  a1       delimiter: blank.
Field 28:40  F13.4 -- Y site coordinate in a crust fixed reference
                      frame. Units: meters.
field 27:27  a1       delimiter: blank.
Field 42:54  F13.4 -- Z site coordinate in a crust fixed reference
                      frame. Units: meters.
field 55:56  a2       delimiter: blanks.
Field 57:64  F8.4  -- Site geocentric latitude, positive to north,
                      in degrees. This field is for information only.
                      Parsing software MUST ignore it.
field 65:65  a1       delimiter: blank.
Field 66:73  F8.4  -- Site longitude, positive towards east,
                      in degrees. This field is for information only.
                      Parsing software MUST ignore it.
field 74:74  a1       delimiter: blank.
Field 75:80  F6.1  -- Site height above the reference ellipsoid in
                      meters. This field is for information only.
                      Parsing software MUST ignore it.

Format of an O-record:
----------------------

Field  1:1    A1      -- Record ID. Should be letter A (decimal code 68).
field  2:3    a2         delimiter: blanks.
Field 14:23   A2      -- Experiment name
field 24:24   a1         delimiter: blanks.
Field 25:46   A1      -- Calendar date in TAI in YYYY.MM.DD-hh:mm:ss.s format
                         Calendar date format:
                         field 1:4   -- I4   Year
                         field 5:5   -- a1   delimiter: .
                         field 6:7   -- I2   Month of the year
                         field 8:8   -- a1   delimiter: .
                         field 9:10  -- I2   Day of the month
                         field 11:11 -- a1   delimiter: -
                         field 12:13 -- I2   Hour
                         field 14:14 -- a1   delimiter: :
                         field 15:16 -- I2   Minute
                         field 17:17 -- a1   delimiter: :
                         field 18:21 -- F4.1 Seconds part
field 47:48   a2         delimiter: blank.
Field 49:56   A8      -- Site identifier
                         in TAI, in seconds. This field is for
                         information only. Parsing software MUST ignore it.
field 57:58   a2         delimiter: blanks.
Field 59:67   F9.5    -- Azimuth   in degrees.
field 68:68   a1         delimiter: blanks.
Field 69:76   F8.5    -- Elevation in degrees.
field 77:78   a2         delimiter: blanks.
Field 79:84   F6.1    -- Surface atmospheric pressure in mbars
field 85:85   a1         delimiter: blanks.
Field 86:90   F5.1    -- Surface air temperature in degrees Celsius.
field 91:92   a2         delimiter: blanks.
Field 93:107  1PD15.7 -- Slanted path delay in seconds of time.
field 108:108 a1         delimiter: blanks.
Field 109:123 1PD15.7 -- Partial derivative of the slanted path delay wrt
                         to the path delay in the direction of the
                         atmosphere symmetry. This direction is usually
                         close to the zenith.
field 124:124 a1         delimiter: blanks.
Field 125:139 1PD15.7 -- Partial derivative of the slanted path delay wrt
                         the tilt of the the direction of the atmosphere
                         symmetry in north direction. Units: seconds of time.
field 140:140 a1         delimiter: blanks.
Field 141:155 1PD15.7 -- Partial derivative of the slanted path delay wrt
                         the tilt of the the direction of the atmosphere
                         symmetry in east direction. Units: seconds of time.

Comments:
---------

  1. Site IDs in this files are ARBITRARY. They do not have any meaning
     and are for internal labeling only. Parsing software SHOULD NOT
     try to use and match them against common station names.
     Site coordinates should be used for matching stations within the
     area of validity defined in record O.

  2. O-records must be sorted in the order of increasing time epochs.
