USNO GPS data is formatted in accordance with the specifications set by the GGTTS. Each common view file consists of a file header which provides information about the GPS equipment used, and the laboratory operating the equipment. Data is then presented for each satellite tracked in the following categories.

Data Category | Explanation |
---|---|

PRN | the satellite vehicle PRN number |

CL | the hexadecimal number that corresponds to the Common View class of the track |

MJD | the five digit Modified Julian Date of the start of the track |

STTIME | hour, minute, and second (in UTC) of the start of the track |

TRKL | the track length in seconds (a full track is 780 seconds) |

ELV | the elevation of the satellite at the midpoint of the track |

AZTH | the azimuth of the satellite at the midpoint of the track |

REFSV | the time difference (measured in .1 nanosecond) between the laboratory reference clock and satellite time, referred to the midpoint of the pass via a linear fit |

SRSV | the slope determined via the linear fit to produce REFSV (measured in .1 picosecond per second) |

REFGPS | the time difference (measured in .1 nanosecond) between the laboratory reference clock and GPS time, referred to the midpoint of the pass via a linear fit |

SRGPS | the slope determined via the linear fit to produce REFGPS (measured in .1 picosecond per second) |

DSG | the root mean square of the residuals of the linear fit used to produce REFGPS |

IOE | the index of ephemeris, a three digit decimal code indicating the ephemeris used for computations |

MDTR | the modeled tropospheric delay (measured in .1 nanosecond) referred to the midpoint of the pass via a linear fit |

SMDT | the slope determined via the linear fit to produce MDTR (measured in .1 picosecond per second) |

MDIO | the modeled ionospheric delay (measured in .1 nanosecond) referred to the midpoint of the pass via a linear fit |

SMDI | the slope determined via the linear fit to produce MDIO (measured in .1 picosecond per second) |

CK | the data line check sum in hexadecimal format, computed as the sum of the ASCII values of the preceeding 101 columns, modulo 256 |

optional | optional data may be presented beyond the check sum column, and is not included in the CK value |

Reference: D. Allan and C. Thomas, Technical Directives for Standardization of GPS
Time Receiver Software, *Metrologica*, 1994, 31, pp. 67-79.

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