About the CGGTTS data format

The Consultative Committee for Time and Frequency (CCTF) advocated in its Recommendation S 5 (2001) that the manufacturers of receivers used for timing with global navigation satellite systems (GNSS) implement the technical guidelines for receiver hardware compiled by the CCTF Group on GNSS Time Transfer Standards (CGGTTS). These guidelines have been compiled with the aim of achieving a system that can transfer time with an accuracy of 1 ns or better. They can be applied to all available global navigation satellite systems, such as GPS, GLONASS, WAAS, EGNOS, MSAS, and Galileo.

USNO GPS data is formatted in accordance with the specifications set by the CGGTTS. 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 CategoryExplanation
PRNthe satellite vehicle PRN number
CLthe hexadecimal number that corresponds to the Common View class of the track
MJDthe five digit Modified Julian Date of the start of the track
STTIMEhour, minute, and second (in UTC) of the start of the track
TRKLthe track length in seconds (a full track is 780 seconds)
ELVthe elevation of the satellite at the midpoint of the track
AZTHthe azimuth of the satellite at the midpoint of the track
REFSVthe 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
SRSVthe slope determined via the linear fit to produce REFSV (measured in .1 picosecond per second)
REFGPSthe time difference (measured in .1 nanosecond) between the laboratory reference clock and GPS system time, referred to the midpoint of the pass via a linear fit
SRGPSthe slope determined via the linear fit to produce REFGPS (measured in .1 picosecond per second)
DSGthe root mean square of the residuals of the linear fit used to produce REFGPS
IOEthe index of ephemeris, a three digit decimal code indicating the ephemeris used for computations
MDTRthe modeled tropospheric delay (measured in .1 nanosecond) referred to the midpoint of the pass via a linear fit
SMDTthe slope determined via the linear fit to produce MDTR (measured in .1 picosecond per second)
MDIOthe modeled ionospheric delay (measured in .1 nanosecond) referred to the midpoint of the pass via a linear fit
SMDIthe slope determined via the linear fit to produce MDIO (measured in .1 picosecond per second)
MSIOthe measured ionospheric delay (measured in .1 nanosecond) referred to the midpoint of the pass via a linear fit, 9999 indicates no data available
SMSIthe slope determined via the linear fit to produce MSIO (measured in .1 picosecond per second)
ISGthe root mean square of the residuals of the linear fit used to produce MSIO
CKthe data line check sum in hexadecimal format, computed as the sum of the ASCII values of the preceding 115 columns, modulo 256
optionaloptional data may be presented beyond the check sum column, and is not included in the CK value

References



US Naval Observatory Home Page
What Time Is It? USNO Time Service Home Page
GPS Home Page at USNO