Trajectory files are created by the Airborne Topographic Mapper team at NASA/GSFC/WFF.
They are ASCII flat files. They are derived from double-differenced dual-frequency
GPS measurements and are computed by the GITAR ("GPS-Inferred Trajectories for Aircraft
and Rockets") analysis package, which was developed in-house by the ATM team. Columns
are labeled, and additional information follows.
Word 1: 1- or 2-digit year
Word 2: Day-of-year
Word 3: Time of day in seconds.
Time is measured according to the GPS time scale, which differs from UTC by
an integer number of seconds according to the addition of leap seconds by the
International Earth Rotation Service. As of mid-July 2010, GPS-UTC=15s
Word 4: Geodetic latitude (decimal degrees). See Note below.
Word 5: Geodetic longitude (decimal degrees). See Note below.
Word 6: Height (meters) measured relative to the WGS-84 ellipsoid. See Note below.
Word 7: Position Dilution of Precision (dimensionless)
Word 8: Vertical Dilution of Precision (dimensionless)
Note: Trajectories are referenced to the most current version of the International
Terrestrial Reference Frame (ITRF) as of the date the mission was flown. As of mid-July
2010, this is ITRF 2005 (shorthanded as ITRF05). Cartesian ITRF coordinates are
converted into geodetic latitude, longitude, and height using the WGS-84 ellipsoid.
The WGS-84 ellipsoid is defined as follows:
semi-major axis: 6378137.0 meters
flattening: 1.0/298.257223563