NGA GPS Ephemeris/Station/Antenna Offset Documentation -- July 01, 2005

NGA GPS Ephemeris/Station/Antenna Offset Documentation
  http://earth-info.nga.mil/GandG/sathtml/gpsdoc2005_07a.html

Effective date July 01, 2005

                     NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY
              GPS PRECISE EPHEMERIDES, SATELLITE CLOCK PARAMETERS
                          AND SMOOTHED OBSERVATIONS

                              PRECISE EPHEMERIS

Earth-centered Earth-fixed trajectory
Coordinate system:  WGS84 (G1150)
Position -- x,y,z (km)
Velocity -- dx/dt,dy/dt,dz/dt (dm/s)
GPS time -- year, day, hour, minute
Trajectory interval:  15 min.
Standard Trajectory referenced to satellite center of mass
Optional Trajectory referenced to satellite antenna phase center


                         SATELLITE CLOCK PARAMETERS

Clock parameters for each satellite:
     Time offset (microseconds)
     Frequency offset (10E-4 microsec/s = parts in 10E10)
Time interval for parameters: 15 min.
Satellite clock events: All events processed as reinitializations


                          SMOOTHED OBSERVATIONS

Smoothed range and range difference observations (km) with corrections
  applied (see below)
GPS time of observation (year, day, seconds from beginning of day)
Standard deviation of observation (km)
Coordinate system:  WGS84 (G1150)
Station coordinates: Position -- x,y,z (m), Epoch 2001.0
                     Velocity -- dx/dt,dy/dt,dz/dt (m/year)
Temperature (degrees Celsius)
Pressure (millibars)
Humidity (percent)
Data interval: 15 min.
Smoothing uses carrier phase to smooth range and range difference
  measurements collected at a 1.5 second rate for NGA and Air Force
  monitor stations and at a 30 second rate for IGS monitor stations
Minimum elevation angle for observation:  10 degrees
National Geospatial-Intelligence Agency and Air Force monitor station data
  collected and smoothed using similar procedures
  References: Computer Program Development Spec., Master Control
  Station, Ephemeris/Clock Computer Program, NAVSTAR GPS Operational
  Control System Segment, CP-MCSEC-302C, Part 1, Appendix A, 7 May 1993.
  Description of the Smoothing Algorithm in the NGA Monitor Station
  Network, (MSN29), Applied Research Laboratories, The University of
  Texas at Austin, GR-SGG-97-1, 3 April 1997.


                            PHYSICAL CONSTANTS

GM(Earth) =  398600.4418 km**3/s**2
GM(Sun)   = 132712400000 km**3/s**2
GM(Moon)  =  4902.799186 km**3/s**2
Moon radius =   1738 km
Sun radius  = 696000 km
Earth semi-major axis (a) = 6378.137  km
Inverse flattening (1/f)  = 298.257223563
Earth angular velocity    = 0.72921158553 X 10**-4 Rad/s
Speed of light  = 299792.458 km/s
Love's constant = 0.290
Solar constant = 4.560 X 10**-6 N/m**2
Astronomical Unit = 149597870.691 km

     STATION COORDINATES (GEODETIC)
                         WGS84 (G1150)  Epoch 2001.0

                       STATION COORDINATES  (CARTESIAN)
                         WGS84 (G1150)  Epoch 2001.0


                           Due to security concerns
                  surrounding the current threat situations,
                  the coordinates for the NGA/Air Force/IGS
                         stations have been removed.

                  Any such information needed about the NGA
                     stations should be requested, until
                     further notice, at:  (314) 263-4120
                               or DSN 693-4120


                     CORRECTIONS APPLIED TO MEASUREMENTS

Ionospheric delay:  2-frequency, 1st order correction
Tropospheric refraction: Saastamoinen hydrostatic and wet zenith delay
  models and Niell hydrostatic and wet mapping functions
Periodic relativistic effects

Satellite antenna offset (satellite body centered coordinates, meters)
  Block II  PRN's  - Delta x=  0.2794, Delta y=  0.0000, Delta z=  0.9519
  Block IIA PRN's  - Delta x=  0.2794, Delta y=  0.0000, Delta z=  0.9519

  Block IIR PRN 02 - Delta x= -0.0099, Delta y=  0.0061, Delta z= -0.0820
  Block IIR PRN 11 - Delta x=  0.0019, Delta y=  0.0011, Delta z=  1.5141
  Block IIR PRN 13 - Delta x=  0.0024, Delta y=  0.0025, Delta z=  1.6140
  Block IIR PRN 14 - Delta x=  0.0018, Delta y=  0.0002, Delta z=  1.6137
  Block IIR PRN 16 - Delta x= -0.0098, Delta y=  0.0060, Delta z=  1.6630
  Block IIR PRN 18 - Delta x= -0.0098, Delta y=  0.0060, Delta z=  1.5923
  Block IIR PRN 19 - Delta x= -0.0079, Delta y=  0.0046, Delta z= -0.0180
  Block IIR PRN 20 - Delta x=  0.0022, Delta y=  0.0014, Delta z=  1.6140
  Block IIR PRN 21 - Delta x=  0.0023, Delta y= -0.0006, Delta z=  1.5840
  Block IIR PRN 22 - Delta x=  0.0018, Delta y= -0.0009, Delta z=  0.0598
  Block IIR PRN 23 - Delta x= -0.0088, Delta y=  0.0035, Delta z=  0.0004
  Block IIR PRN 28 - Delta x=  0.0019, Delta y=  0.0007, Delta z=  1.5131

Station displacement due to tides
Yaw Bias: JPL yaw bias model for  Block II and IIA satellites in eclipse


                              FORCE MODELING

Gravitational:
     EGM96 Earth gravity model truncated at degree 12 and order 12
     Solar and Lunar gravity using the DE403 ephemeredes, J2000 epoch,
       and IAU Resolutions on Astronomical Constants, Time Scales, and
       the Fundamental Reference Frame (1976-1980)
     Solid Earth tides

Non-gravitational:
     Radiation Pressure
       The JPL TJPLXYZ03-II/IIA version model for Block II and IIA satellites
       The JPL TJPLXYZ03-IIR version model for Block IIR satellites
     Thrusts
     Momentum dumps

Kinematic:
     Luni-solar and planetary precession (IAU Resolutions, as above)
     Nutation (IAU Resolutions, as above)
     Earth rotation (IAU Resolutions, as above)
     Polar Motion (using NGA initial values generated the week before
       the orbit fit) + diurnal and semi-diurnal effects
     UT1-UTC (using NGA initial values generated the week before the
       orbit fit) + Zonal tide effects + diurnal and semi-diurnal effects

Integration step size:  300 seconds, reduced to 10 seconds during
  eclipse boundary crossings


                        ORBIT ESTIMATION METHOD

Kalman Filter/RTS Smoother (Square Root Information implementation)
Initial conditions: From previous fit
Solution parameters:
	Satellite state vector in element form at trajectory epoch --
	  semi-major axis
	  eccentricity * sin(argument of perigee)
	  eccentricity * cos(argument of perigee)
	  inclination
	  mean anomaly + argument of perigee
	  right ascension of the ascending node
	Satellite clock parameters -- Time offset, Frequency offset
	Monitor station clock parameters (excluding master station) --
          Time offset, Frequency offset
	Polar motion parameters -- Pole and pole rate components along
          Greenwich meridian, Pole and pole rate components along
          meridian 90 deg west of Greenwich, Rate of change and
          acceleration of UT1-UTC
	Satellite radiation pressure parameters -- Radiation pressure
          scale, and Y-axis acceleration
        Tropospheric refraction -- One stochastic zenith delay
          parameter per station
Minimum range observation uncertainty(1-sigma):100 cm (IGS Stations)
                                                80 cm (AF Station 85130)
                                                40 cm (Other AF and NGA stations)
Minimum range difference observation uncertainty (1-sigma): 1.5 cm
Process noise in Kalman Filter:
        Radiation pressure (each satellite)--
	     Decorrelation time   14,400 s
	     Steady state sigmas --
	        SCALE   0.05
	        Y-AXIS  0.5 X 10**-12 km/s**2
	Tropospheric refraction variance rate: 2.89 cm**2/hr
	Station clock white noise spectral density: (each station) --
	     Time offset       0.1111 X 10**-2 (microseconds)**2/s
	     Frequency offset  0.1111 X 10**-8 (ppm)**2/s
	Satellite clock white noise spectral density: (each satellite)
           Time offset       0.1111 X 10**-2 (microseconds)**2/s
	     Frequency offset  0.1111 X 10**-8 (ppm)**2/s
	     Frequency drift   0.              (ppm/s)**2/s


                     SATELLITE CLOCK ESTIMATION METHOD

Kalman Filter/RTS Smoother (Square Root Information implementation)
Orbit solutions from above method are held fixed for satellite clock
  estimation
Solution parameters:
    Satellite clock parameters -- Time offset, Frequency offset		
    Monitor station clock parameters (excluding master station) --
      Time offset, Frequency offset
    Tropospheric refraction -- One stochastic zenith delay parameter
      per station.
Minimum range observation uncertainty(1-sigma):100 cm (IGS Stations)
                                                80 cm (AF Station 85130)
                                                40 cm (Other AF and NGA stations)
Minimum range difference observation uncertainty (1-sigma): 15.0 cm
Process noise in Kalman Filter:
    Tropospheric refraction variance rate: 2.89 cm**2/hr

    Station clock white noise spectral densities:
      NGA stations (except USNO) and Air Force stations (except Colorado Springs):
             Time offset       0.1944 X 10**-8  (microseconds)**2/s
             Frequency offset  0.4440 X 10**-19 (ppm)**2/s
      NGA station at USNO and Air Force station at Colorado Springs:
             Time offset       0.1380 X 10**-9  (microseconds)**2/s
             Frequency offset  0.4440 X 10**-19 (ppm)**2/s
	IGS stations:
             Time offset       0.3456 X 10**-8  (microseconds)**2/s
             Frequency offset  0.4440 X 10**-19 (ppm)**2/s

    Satellite clock white noise spectral densities:
	Satellite Block IIR Rubidium clocks
             Time offset       0.8640 X 10**-9  (microseconds)**2/s
             Frequency offset  0.1110 X 10**-18 (ppm)**2/s
	     Frequency drift   0.               (ppm/s)**2/s
        Satellite Block II/IIA Rubidium clocks
             Time offset       0.1944 X 10**-8  (microseconds)**2/s
             Frequency offset  0.1110 X 10**-18 (ppm)**2/s
             Frequency drift   0.               (ppm/s)**2/s
        Satellite Cesium clocks
             Time offset       0.13824 X 10**-7 (microseconds)**2/s
             Frequency offset  0.1000 X 10**-17 (ppm)**2/s
	     Frequency drift   0.               (ppm/s)**2/s
	Satellite 'Noisy' Cesium clocks
             Time offset       0.2000 X 10**-7  (microseconds)**2/s
	     Frequency offset  0.1110 X 10**-16 (ppm)**2/s
             Frequency drift   0.               (ppm/s)**2/s


Reference:  Swift, E., Mathematical Description of the GPS Multi-Satellite
  Filter/Smoother, NSWCDD Report (Oct. 2001).




.

Relevant Pages
Loading