The data are placed in files called
The content of this file is in development. At present this file contains just numbers of launched satellites, changes in their configuration, and inserting or removing the satellite from the almanac. We are going to keep this file up to date.
The file iono.gps contents archive of ionospheric parameters from the GPS almanac.
In the file health.gps is a list of detected satellite drop-outs indicated in the almanac .
The almanac data are the subset of the clock and ephemeris parameters with reduced precision. The almanac parameters are updated usually at least once a week. We will update the almanac as quickly as possible. You should find the newest almanac in almanac.gps file. Every data item is preceeded by a variable name. Variable name conventions: all names were chosen so that they would match the symbols used in the NATO STANAG. Most of the variables contain a subscript. Each subscript is separated from a variable name by a slash (”/”). Greek symbols are rewritten following their pronunciation and they are distinguished from other letters of a variable name by underscore (“_”). The value and the name of a variable are split by equal sign (”=”).
The file almanac.gps consists of three parts:
***** 1) HEADER ***** The header of this file is self explaining. Example: ALMANAC was received on 14 Jan 1994, 12:45:21 UTC ***** 2) UTC AND IONOSPHERE DATA ***** UTC and IONO blocks contain coefficients from page 18 of subframe 4. UTC block begins with a keyword "UTC:". It contains the parameters needed to relate GPS time to UTC (USNO) time: A/1 First order term of polynomial units [s/s]; range approx. (-7.5ns/s, 7.5ns/s) A/0 Constant term of polynomial units [s]; range approx. (-2s, 2s) t/ot Reference time for UTC data units [s]; range (0, 602112) WN/t UTC reference week number units [weeks]; range (0, 1023) DELTA_t/LS Time difference due to leap seconds units [s]; range (-128, 127) WN/LSF Week number at the end of which the leap seconds become effective units [weeks]; range (0, 1023) DN Day number at the end of which the leap seconds become effective units [days]; range (1, 7) DELTA_t/LSF Difference due to leap seconds units [s]; range (-128, 127) IONO block begins with a keyword "IONO:". It contains current coefficients for eight-coefficient (Klobuchar) model of ionosphere: alpha/0..3 four alfa coefficients units [s s/semicircle s/semicircle^2 s/semicircle^3]; ranges approx. (+-120ns) (+-954ns/semicircles) (+-7.6us/semicircles^2) (+-7.6us/semicircles^3) beta/0..3 four beta coefficients units [s s/semicircle s/semicircle^2 s/semicircle^3]; ranges approx. (+- 260000) (+-2100000) (+-8400000) (+-8400000) Example: UTC: A/1 = 4.707346E-0014 A/0 = 1.862645E-0008 t/ot = 118784 WN/t = 732 DELTA_t/LS = 9 WN/LSF = 703 DN = 3 DELTA_t/LSF = 9 IONO: alpha/0..3 = 1.117587E-0008 -7.450581E-0009 -5.960464E-0008 1.192093E-0007 beta/0..3 = 1.146880E+0005 -1.638400E+0005 -1.966080E+0005 9.175040E+0005 ***** 3) SATELLITES DATA ***** These data come from subframe 4 (pages 2 through 5 and 7 through 10 and page 25) and subframe 5 (all pages). Satellite data begin with a keyword "ALM:". Satellites are distinguished from each other by an empty line. SV_ID Space vehicle - satellite identifier [dimensionless]; range (1, 32) A-S Anti-Spoofing; P-code encryption (ON, OFF) Block Configuration of satellite (1, 2) Health 8-bits health word (the 5 LSB bits provide the health status of signal components and 3 MSB bits (range 0..255) The meaning in the health word is translated to readable form (BAD/GOOD) in parantheses behind the value t/oa Reference time of almanac units [seconds in week]; range (0..602112) step 4096 WN/a Reference week of almanac units [weeks]; range (0, 1023) e Eccentricity [dimensionless]; range approx. (0, 0.032) i Inclination angle units [semicircles]; range approx.(0.23, 0.37) sqrt(A) Square root of the semi-major axis units [metres^1/2]; range approx. (0, 8200) OMEGA/0 Longitude of ascending node of orbit plane at weekly epoch units [semicircles]; range (+-1) OMEGA_DOT Rate of right ascension units [semicircle/second]; range (+-120e-9) omega Argument of perigee units [semicircles]; range (+-1) M/0 Mean anomaly at reference time units [semicircles]; range (+-1) a/f0 Satellite PRN code phase time offset units [s]; range (+-1ms) a/f1 Satellite PRN code relative frequency offset units [s/s]; range approx. (+-4ns/s) N.B. 1 semicircle= 1 rad/PI Example: ALM: SV_ID = 1 A-S = OFF Block = 2 Health = 0 ( Signal = GOOD , Data = GOOD ) t/oa = 118784 WN/a = 732 e = 3.47614288330078E-0003 i = 3.00995635986328E-0001 sqrt(A) = 5.15362451171875E+0003 OMEGA/0 = 4.99201297760009E-0001 OMEGA_DOT = -2.53930920735001E-0009 omega = -3.57437849044800E-0001 M/0 = -5.23125290870666E-0001 a/f0 = -4.57763671875000E-0005 a/f1 = -2.03726813197136E-0010 SV_ID = 2 A-S = OFF Block = 2 Health = 0 ( Signal = GOOD , Data = GOOD ) t/oa = 118784 ... etc.