TOC | | | | | INDEX
NOAA's Analysis Center Questionaire
The models and processing strategy used in orbit production
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INTERNATIONAL GPS SERVICE FOR GEODYNAMICS
NOAA/NGS Analysis Strategy Summary
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ANALYSIS CENTRE | National Oceanic and Atmospheric Administration (NOAA)
| National Geodetic Survey (NGS)
| Phone: 301-713-3205, Fax: 301-713-4322
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CONTACT PERSON(S) | Operations:
| William Kass email: billk@buster.ngs.noaa.gov
| phone : 301-713-3208
| Paul Spofford email: pauls@dancer.ngs.noaa.gov
| phone : 301-713-3205
| Analysis Software:
| Steve Hilla email: Steve.Hilla@noaa.gov
| phone : 301-713-2854
| Jim Ray email: jimr@ray.grdl.noaa.gov
| phone : 301-713-2850
| Gerald Mader email: gerry@mozart.grdl.noaa.gov
| phone : 301-713-2854
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SOFTWARE USED | page4 developed at NOAA
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IGS PRODUCTS | NGS0wwwn.EPH GPS ephemeris/clock files in 7 daily
GENERATED FOR | files at 15 min intervals in SP3 format,
GPS WEEK 'www' | including accuracy codes computed from
DAY OF WEEK 'n' | the formal orbit errors of the solution
(n=0,1,...,6) | NGS0wwwn.ERP EOP (pole and LOD estimates; a priori
| UT1-UTC) in 7 daily files
| NGS0wwwn.SUM Processing summary in 7 daily files
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PREPARATION DATE | Sep. 19, 1995
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EFFECTIVE DATE FOR | Aug. 06, 1995
DATA ANALYSIS |
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| MEASUREMENT MODELS |
|---------------------------------------------------------------------------|
| Preprocessing | Phase preprocessing in a baseline by baseline mode |
| | using double-differences. In most cases cycle slips |
| | are fixed automatically looking simultaneously at |
| | different linear combinations of L1 and L2. Manual |
| | re-editting is done if any baseline shows larger |
| | than normal post-fit RMS statistics in the all base- |
| | combined solution. At that time, bad data points are |
| | removed or new ambiguities are set up. |
|---------------------------------------------------------------------------|
| Basic observable | Carrier phase, code only used for receiver clock sync. |
| |--------------------------------------------------------|
| | Elevation angle cutoff : 15 degrees |
| | Sampling rate : 30 seconds |
| | Weighting : uniform |
| | Rejection criteria : No rejection during parameter|
| | estimation. Outliers marked |
| | during preprocessing step; |
| | manual re-edit done for any |
| | baseline with high RMS fit. |
|---------------------------------------------------------------------------|
| Modelled | Double-differences, ionosphere-free linear combination.|
| observable | |
|---------------------------------------------------------------------------|
| RHC phase | applied (Wu et al., 1993) |
| rotation corr. | |
|---------------------------------------------------------------------------|
| Ground antenna | Elevation-dependent phase center corrections are |
| phase centre | applied to all antenna types (Mader & MacKay, 1995) |
|---------------------------------------------------------------------------|
| Troposphere | A priori zenith : Saastamoinen (1972) "dry" + "wet" |
| | delay zenith delays |
| |--------------------------------------------------------|
| | Mapping function: NMF dry and wet mapping functions |
| | (Niell, 1995) |
| |--------------------------------------------------------|
| | Met. data input : latitude, height, DOY model |
| |--------------------------------------------------------|
| | Estimation : wet zenith delay adjusted in 2-hour |
| | intervals for all sites |
|---------------------------------------------------------------------------|
| Ionosphere | Not modelled (ionosphere eliminated by forming the |
| | ionosphere-free linear combination of L1 and L2) |
|---------------------------------------------------------------------------|
| Plate motions | ITRF93 station velocities fixed (see IGSMAIL#819) |
|---------------------------------------------------------------------------|
| Tidal | Solid earth tidal : Cartwright & Taylor (1971) tidal |
| displacements | displacement potential complete thru degree 3 |
| | with newest Shida and Love numbers |
| | (Mathews et al., unpublished) |
| | Correction applied: zero-frequency contribution not |
| | to remove removed |
| | permanent tide |
| | Nominal Love nos. : h2 = 0.6067; el2 = 0.0844 |
| | h3 = 0.2900 el3 = 0.0152 |
| | dh resonance : applied for 6 largest tides |
| | corrections |
| |--------------------------------------------------------|
| | Pole tide : not applied |
| |--------------------------------------------------------|
| | Ocean loading : not applied |
|---------------------------------------------------------------------------|
| Earth orientation| Tidal UT1 (>5day) : not modelled |
| models | Sub-daily EOP : Herring & Dong (1994) model applied|
|---------------------------------------------------------------------------|
| Atmospheric load.| not applied |
|---------------------------------------------------------------------------|
| Satellite center | Block I x,y,z: 0.2110, 0.0000, 0.8540 m |
| of mass |--------------------------------------------------------|
| correction | Block II/IIA x,y,z: 0.2790, 0.0000, 1.0230 m |
|---------------------------------------------------------------------------|
| Satellite phase | not applied |
| centre calibrat. | |
|---------------------------------------------------------------------------|
| Relativity | periodic corrections applied |
|---------------------------------------------------------------------------|
| GPS attitude | not applied |
| model | |
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| ORBIT MODELS |
|---------------------------------------------------------------------------|
| Geopotential | GEM-T3 model up to degree and order 8; |
| | C21, S21 as recommended by IERS (1992) |
| |--------------------------------------------------------|
| | GM = 398600.4418 km**3/sec**2 |
| |--------------------------------------------------------|
| | AE = 6378.1363 km |
|---------------------------------------------------------------------------|
| Third-body | Sun and Moon as point masses |
| |--------------------------------------------------------|
| | Ephemeris: Generated from the MIT PEP program |
| |--------------------------------------------------------|
| | GMsun = 132712440000 km**3/sec**2 |
| |--------------------------------------------------------|
| | GMmoon = 4902.7989 km**3/sec**2 |
|---------------------------------------------------------------------------|
| Solar radiation | Direct radiation: ROCK4 and ROCK42 models (T10 and T20)|
| pressure | for Block I and II satellites, resp. |
| | (Fliegel et al., 1992) |
| | Satellite masses: |
| | PRN 01 972.9 kg PRN 15 885.9 kg |
| | PRN 02 878.2 kg PRN 16-19 883.2 kg |
| | PRN 05-07 972.9 kg PRN 20 887.4 kg |
| | PRN 09 972.9 kg PRN 21-22 883.9 kg |
| | PRN 12 519.8 kg PRN 23-29 972.9 kg |
| | PRN 14 887.4 kg PRN 31 972.9 kg |
| |--------------------------------------------------------|
| | x-scale, y-bias : offset adjustment for each 1-day arc |
| |--------------------------------------------------------|
| | Earth shadow model includes: umbra and penumbra |
| |--------------------------------------------------------|
| | Reflection radiation: not included |
| |--------------------------------------------------------|
| | New GPS satellite attitude model: not applied |
| | Geometrical effects : not applied |
| | Orbit dynamic effects : not applied |
| | Yaw rates : -- |
|---------------------------------------------------------------------------|
| Tidal forces | Solid earth tides: C20, C21, S21, C22, and S22 as in |
| | IERS (1992); n=2 order-dependent |
| | Love numbers and frequency-dependent|
| | corrections for 6 (2,1) tides from |
| | Richard Eanes (private comm., 1995) |
| |--------------------------------------------------------|
| | Ocean tides : not applied |
|---------------------------------------------------------------------------|
| Numerical | 11th order Adams-Moulton Predictor-corrector |
| Integration | |
| |--------------------------------------------------------|
| | Integration step : variable |
| |--------------------------------------------------------|
| | Starter procedure: Initial conditions taken from the |
| | previous day at 23:45 (from |
| | broadcast under special conditions).|
| |--------------------------------------------------------|
| | Arc length : 24 hours |
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| ESTIMATED PARAMETERS (APRIORI VALUES & SIGMAS) |
|---------------------------------------------------------------------------|
| Adjustment | Least-squares algorithms using 24 hours of double- |
| | differenced phase observations from the global network.|
|---------------------------------------------------------------------------|
| Station | Standard 13 stations fixed to the ITRF93 positions as |
| coordinates | given in IGSMAIL#819, plus MDO1 and MATE also fixed. |
| | The ITRF93 velocities are used for coordinate updates. |
| | All remaining stations estimated. |
|---------------------------------------------------------------------------|
| Satellite clock | Satellite clock biases are not estimated but elimi- |
| bias | nated by forming double-differences. |
|---------------------------------------------------------------------------|
| Receiver clock | Receiver clock corrections are estimated during the |
| bias | pre-processing using code measurements. |
|---------------------------------------------------------------------------|
| Orbital | Geocentric position and velocity, solar radiation |
| parameters | pressure scales in x and y SV directions estimated as |
| | constant offsets for each one-day arc. |
|---------------------------------------------------------------------------|
| GPS attitude | none estimated |
| parameters | |
|---------------------------------------------------------------------------|
| Troposphere | Wet zenith delay estimated as constant offset for 2-hr |
| | intervals at each station. |
|---------------------------------------------------------------------------|
| Ionospheric | Not estimated; L1 & L2 used for 1st order corrections |
| correction | |
|---------------------------------------------------------------------------|
| Ambiguity | Estimated as real values with no a priori constraints |
|---------------------------------------------------------------------------|
| EOP | x and y pole and LOD estimated as constant offsets for |
| | each one-day arc. A priori values taken from IERS |
| | Rapid Service Bulletin A. |
|---------------------------------------------------------------------------|
| Other | None |
| parameters | |
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| REFERENCE FRAMES |
|---------------------------------------------------------------------------|
| Inertial | Geocentric; mean equator and equinox of Besselian year |
| | 1950 (B1950.0) |
|---------------------------------------------------------------------------|
| Terrestrial | ITRF93 reference frame realized through a set of 15 |
| | station coordinates and velocities as given in IGSMAIL |
| | #819 as well as the antenna offsets for the above |
| | stations given in /igscb/station/tie/localtie.tab |
| | (available from IGS at sideshow.jpl.nasa.gov). |
|---------------------------------------------------------------------------|
| Interconnection | Precession: IAU 1976 Precession Theory |
| |--------------------------------------------------------|
| | Nutation: IAU 1980 Nutation Theory |
| |--------------------------------------------------------|
| | Relationship between UT1 and GMST: USNO Circular |
| | No. 163 (IAU Res.) |
| |--------------------------------------------------------|
| | A priori EOP values: from IERS Rapid Service Bull. A |
| |--------------------------------------------------------|
| | Tidal UT1 (>5day) : not modelled |
| | Sub-daily EOP : not modelled |
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REFERENCES:
Cartwright, D.E., and R.J. Taylor, New computations of the tide-
generating potential, Geophys. J.R. astr. Soc., 23, 45-74, 1971;
Cartwright, D.E., and A.C. Edden, Corrected tables of tidal harmonics,
ibid, 33, 253-264, 1973.
Fliegel, H., T. Gallini and E. Swift, Global Positioning System
radiation force model for geodetic applications, J. Geophys. Res. 97(B1),
559-568, 1992.
Herring, T.A., and D. Dong, Measurement of diurnal and semidiurnal
rotational variations and tidal parameters of Earth, J. Geophys. Res.,
99(B9), 18051-18071, 1994.
Mader, G.L. and J.R. MacKay, Calibration of GPS antennas, in preparation,
1995.
McCarthy, D.D. (ed.), IERS Standards (1992), IERS Technical Note 13,
Observatoire de Paris, 1992.
Niell, A.E., Global mapping functions for the atmosphere delay at radio
wavelengths, submitted to J. Geophys. Res., 1995.
Saastamoinen, J., Atmospheric correction for the troposphere and
stratosphere in radio ranging of satellites, in The Use of Artificial
Satellites for Geodesy, Geophys. Monogr. Ser. 15 (S.W. Henriksen et al.,
eds.), AGU, Washington, D.C., pp. 247-251, 1972.
Wu, J.T., S.C. Wu, G.A. Hajj, W.I. Bertiger, and S.M. Lichten, Effects of
antenna orientation on GPS carrier phase, Manuscripta Geodaetica, 18,
91-98, 1993.
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September 10, 1996
Steve Hilla