GPS

The data are placed in files called

Older data files (1994-2011) you can find here: health_a.gps, iono.gps, iono_a.gps.

Organization of status.gps file:

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.

Organization of ionospheric parameters:

The file iono.gps contents archive of ionospheric parameters from the GPS almanac.

Organization of satellite health drop-outs file:

In the file health.gps is a list of detected satellite drop-outs indicated in the almanac .

Organization of almanac data:

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
  2. UTC and ionosphere data
  3. Satellites data
 *****  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.
 
 
almanacs/gps.txt · Last modified: 2013/01/24 10:18 by webadmin
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