NGA GPS Ephemeris/Station/Antenna Offset Documentation

NGA GPS Ephemeris/Station/Antenna Offset Documentation
Ref: http://earth-info.nga.mil/GandG/sathtml/gpsdoc2005_04a.html
Effective date April 08, 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 NIMA and Air Force
monitor stations and at a 30 second rate for IGS monitor stations
Minimum elevation angle for observation: 10 degrees
National Imagery and Mapping 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 NIMA 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 NIMA initial values generated the week before
the orbit fit) + diurnal and semi-diurnal effects
UT1-UTC (using NIMA 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)
100 cm (Station 85128)
80 cm (Station 85130)
40 cm (other 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)
100 cm (Station 85128)
80 cm (Station 85130)
40 cm (other 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 and Air Force Colorado Springs station:
Time offset 0.1944 X 10**-8 (microseconds)**2/s
Frequency offset 0.4440 X 10**-19 (ppm)**2/s
        Air Force stations (except Colorado Springs) and 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).