NGA GPS Ephemeris/Station/Antenna Offset Documentation
Effective date June 1, 2010
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 (CARTESIAN)
WGS84 (G1150) Epoch 2001.0
COORDINATES ARE IN METERS
VELOCITIES ARE IN METERS/YEAR
ID X (m) Y (m) Z (m)
85128) AMC1 -1248599.616 -4819441.045 3976490.143
-.0179 .0010 -.0037
85129) ASCN 6118523.959 -1572350.788 -876463.966
-.0025 -.0048 .0102
85130) DGAR 1916197.038 6029998.760 -801737.324
-.0422 .0203 .0307
85131) KWGL -6160884.189 1339851.890 960843.048
.0207 .0673 .0270
85132) HAWI -5511980.267 -2200247.059 2329480.888
-.0095 .0630 .0298
85143) CAPE 918988.120 -5534552.966 3023721.377
-.0102 -.0015 .0015
--------------------------------------------------
85402) AUSA -3939182.131 3467075.376 -3613220.824
-.0408 .0036 .0473
85403) ARGA 2745499.065 -4483636.591 -3599054.582
.0021 -.0100 .0070
85404) ENGD 3981776.642 -89239.095 4965284.650
-.0138 .0165 .0077
85405) BAH1 3633910.281 4425277.149 2799862.429
-.0297 .0091 .0253
85406) ECUA 1272867.329 -6252772.124 -23801.818
.0030 .0004 .0099
85407) USNO 1112160.327 -4842854.274 3985496.368
-.0148 -.0001 .0010
85410) ALAS -2296298.460 -1484805.050 5743080.090
-.0222 -.0036 -.0092
85411) NZLD -4780787.718 436877.170 -4185259.709
-.0235 .0192 .0220
85412) SAFR 5066232.133 2719226.969 -2754392.735
.0001 .0209 .0140
85413) SKOR -3067863.123 4067641.035 3824295.830
-.0290 -.0076 -.0102
85414) TAHI -5246403.866 -3077285.554 -1913839.459
-.0425 .0468 .0291
STATION COORDINATES (GEODETIC)
WGS84 (G1150) Epoch 2001.0
ID LAT (deg N) LONG (deg E) ELLIPSOID HT (m)
85128) 38.80293823 255.47540511 1911.811
85129) -7.95132970 345.58786971 106.382
85130) -7.26984340 72.37092199 -64.333
85131) 8.72250080 167.73052657 39.733
85132) 21.56149103 201.76066969 425.854
85143) 28.48373800 279.42769549 -24.005
--------------------------------------------------
85402) -34.72900041 138.64734499 38.155
85403) -34.57370168 301.48070059 48.747
85404) 51.45374284 358.71610888 163.097
85405) 26.20914022 50.60814451 -14.707
85406) -.21515762 281.50639203 2922.537
85407) 38.92056568 282.93370406 57.872
85410) 64.68794025 212.88703366 176.570
85411) -41.27264988 174.77870783 47.892
85412) -25.74634609 28.22403736 1416.405
85413) 37.07756804 127.02403172 51.792
85414) -17.57703053 210.39381438 99.927
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
Block IIR-M PRN 01 - Delta x= 0.01245, Delta y= -0.00038, Delta z= -0.02283
Block IIR-M PRN 05 - Delta x= 0.00292, Delta y= -0.00005, Delta z= -0.01671
Block IIR-M PRN 07 - Delta x= 0.00127, Delta y= 0.00025, Delta z= 0.00056
Block IIR-M PRN 12 - Delta x= -0.01016, Delta y= 0.00587, Delta z= -0.09355
Block IIR-M PRN 15 - Delta x= -0.00996, Delta y= 0.00579, Delta z= -0.01227
Block IIR-M PRN 17 - Delta x= -0.00996, Delta y= 0.00599, Delta z= -0.10060
Block IIR-M PRN 29 - Delta x= -0.01012, Delta y= 0.00591, Delta z= -0.01512
Block IIR-M PRN 31 - Delta x= 0.00160, Delta y= 0.00033, Delta z= -0.05750
Block IIF PRN 25 - Delta x= 0.39200, Delta y= 0.00200, Delta z= 1.09300
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
The ?????? - IIF version model for Block IIF 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/IIF 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).
Point of Contact: GPS Branch
Phone Numbers:
Com. (314)676-9142
DSN 846-9142
Email: gps@nga.mil
