Subject: [IGSMAIL-0695] NOAA Analysis Center Survey
From: M. Schenewerk
Date: Tue, 2 Aug 1994 13:59:35 PDT

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IGS Electronic Mail      Tue Aug  2 13:59:35 PDT 1994      Message Number 0695
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Author: M. Schenewerk
Subject: NOAA Analysis Center Survey

Subject: NOAA Analysis Center Questionnaire

             INTERNATIONAL GPS SERVICE FOR GEODYNAMICS

        	     Analysis Centre Questionnaire

-----------------------------------------------------------------------------
|                           GENERAL INFORMATION                             |
|---------------------------------------------------------------------------|
| Analysis Centre  | National Oceanic and Atmospheric Administration (NOAA) | 
|                  | National Geodetic Survey (NGS)                         |
|                  | SSMC3; N/CG14                                          |
|                  | 1315 East-West Highway                                 |
|                  | Silver Spring, MD  20910                               |
|                  | USA                                                    |
|                  | Phone: 301-713-3205,        Fax: 301-713-4322          |
|---------------------------------------------------------------------------|
| Contact Person(s)| Mark Schenewerk   e-mail: [email-masked]      |
|                  |                   phone : 301-713-2854                 |
|                  | William Kass      e-mail: [email-masked]    |
|                  |                   phone : 301-713-3208                 |
|                  | Gerald Mader      e-mail: [email-masked]   |
|                  |                   phone : 301-713-2854                 |
|                  | Paul Spofford     e-mail: [email-masked]    |
|                  |                   phone : 301-713-3205                 |
|---------------------------------------------------------------------------| 
| Software Used    | PAGE3 developed at NOAA                                |
|---------------------------------------------------------------------------|
| IGS Products     | NGSwwwwn.EPH  GPS ephemeris/clock files in 7 daily     |
| generated for    |               files at 15 min intervals in SP3 format, |
| GPS week 'wwww'  |               including accuracy codes computed from   |
| day of week 'n'  |               the formal orbit errors of the solution  |
| (n=0,1,...,6)    | NGSwwwwn.ERP  ERP (pole estimates and a priori UT1-UTC)|
|                  |               in 7 daily files                         |
|                  | NGSwwwwn.SUM  Processing summary in 7 daily files      |
|---------------------------------------------------------------------------|
| Preparation Date | July 18, 1994                                          |
-----------------------------------------------------------------------------
 
-----------------------------------------------------------------------------
|                           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 :  20 degrees                   |
|                  | Sampling rate          :  30 seconds                   |
|                  | Weighting              : Uniform                       |
|---------------------------------------------------------------------------| 
| Modelled         | Double-differences, ionosphere-free linear combination.|
| observable       |                                                        |
|---------------------------------------------------------------------------| 
| RHC phase        | None                                                   |
| rotation corr.   |                                                        |
|---------------------------------------------------------------------------|
| Ground antenna   | Elevation-dependent phase center corrections are       |
| phase centre     | applied to all antenna types.                          |
|---------------------------------------------------------------------------|
| Troposphere      | A priori model: Saastamoinen "dry" zenith with the     |
|                  | CfA 2.2 mapping function plus the Chao "wet" zenith    |
|                  | with the Saastamoinen "wet" mapping function.          |
|                  |--------------------------------------------------------| 
|                  | Estimation      : zenith delays in 6 hour intervals.   |
|---------------------------------------------------------------------------| 
| Ionosphere       | Not modelled (ionosphere eliminated by forming the     |
|                  | ionosphere-free linear combination of L1 and L2)       |
|---------------------------------------------------------------------------| 
| Plate motions    | ITRF92 station velocities fixed (see IGSMAIL#421)      |
|---------------------------------------------------------------------------| 
| Tidal            | Solid earth tidal displacement: Melchion (1978)        | 
| displacements    |--------------------------------------------------------| 
|                  | Pole tide: not applied                                 |
|                  |--------------------------------------------------------| 
|                  | Ocean loading: not 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. |                                                        |
-----------------------------------------------------------------------------

----------------------------------------------------------------------------- 
|                             ORBIT MODELS                                  |
|---------------------------------------------------------------------------| 
| Geopotential     | GEMT3 model up to degree and order 8                   |
|                  |--------------------------------------------------------| 
|                  | 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 approximations (T10 |
| pressure         |                   and T20) for Block I and II sat.     |
|                  |                                                        |
|                  | Satellite masses used:                                 |
|                  |  all Block I = 520.0 kg                                |
|                  |  all Block II= 885.0 kg                                |
|                  |--------------------------------------------------------| 
|                  | One scale factor and the y-bias estimated per arc      |
|                  |--------------------------------------------------------| 
|                  | Earth shadow model includes: umbra and penumbra        |
|                  |--------------------------------------------------------| 
|                  | Reflection radiation: not included                     |
|                  |--------------------------------------------------------|
|                  | New GPS satellite attitude model: not applied          |
|---------------------------------------------------------------------------| 
| Tidal forces     | Solid earth tides: not applied                         |
|                  |--------------------------------------------------------| 
|                  | Ocean tides: not applied                               |
|---------------------------------------------------------------------------| 
| Relativity       | Not applied                                            |
|---------------------------------------------------------------------------| 
| Numerical        | 11th order Adams-Moulton Predictor-corrector           | 
| Integration      |                                                        |
|                  |--------------------------------------------------------|
|                  | Integration step: 22.5 minutes                         |
|                  |--------------------------------------------------------| 
|                  | Starter procedure: Initial conditions taken from the   |
|                  | previous day at 24:00 (from broadcast under special    |
|                  | conditions).                                           |
|                  |--------------------------------------------------------| 
|                  | Arc length: 31 hours (3.5 + 24 + 3.5)                  |
----------------------------------------------------------------------------- 

----------------------------------------------------------------------------- 
|               ESTIMATED PARAMETERS (APRIORI VALUES & SIGMAS)              |
|---------------------------------------------------------------------------| 
| Adjustment       | Least-squares algorithms using 24 hours of double-     |
|                  | differenced phase observations from the global network.|
|---------------------------------------------------------------------------| 
| Rejection Criter.| No rejection during parameter estimation procedure.    |
|                  | Outliers are marked during pre-processing step         |
|---------------------------------------------------------------------------|
| Station          | 13 stations absolutely fixed to the ITRF92 positions   |
| coordinates      | as given in IGSMAIL#421 and #430, the remaining are    |
|                  | estimated.  The ITRF92 velocities are used for daily   |
|                  | coordinate updates.  Other site positions defined in   |
|                  | IGSMAIL#421 and #430.                                  |
|                  | Beginning with data from July 20, 1994, an additional  |
|                  | 12 sites are fixed.                                    |
|---------------------------------------------------------------------------| 
| Orbital          | 6 element state vector at IC, solar radiation and      |
| parameters       | y-bias scaling factors estimated as constants for one  | 
|                  | arc. No a priori sigmas used.                          |
|---------------------------------------------------------------------------| 
| Troposphere      | Zenith delays estimated once per 6 hours for each      |
|                  | station.                                               |
|---------------------------------------------------------------------------| 
| Ionospheric      | Not estimated                                          |
| correction       |                                                        |
|---------------------------------------------------------------------------| 
| Ambiguity        | Estimated as real values with no a priori constraints  |
|---------------------------------------------------------------------------| 
| ERP              | X- and Y-pole coordinates.                             |
|                  | A priori values taken from IGS Rapid Service Bulletin. |
|---------------------------------------------------------------------------| 
| 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.                |
|---------------------------------------------------------------------------|
| Other            | None                                                   |
| parameters       |                                                        |
----------------------------------------------------------------------------- 

----------------------------------------------------------------------------- 
|                            REFERENCE FRAMES                               |
|---------------------------------------------------------------------------| 
| Inertial         | Geocentric; mean equator and equinox of Besselian year |
|                  | 1950 (B1950.0)                                         |
|---------------------------------------------------------------------------| 
| Terrestrial      | ITRF92 reference frame realized through a set of 13    |
|                  | station coordinates and velocities as given in IGSMAIL |
|                  | #421 and #430 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).         |
|                  | Beginning with data from July 20, 1994, an additional  |
|                  | 12 sites were fixed.                                   |
|---------------------------------------------------------------------------| 
| Interconnection  | Precession: IAU 1976 Precession Theory                 | 
|                  |--------------------------------------------------------|
|                  | Nutation: IAU 1980 Nutation Theory                     |
|                  |--------------------------------------------------------| 
|                  | Relationship between UT1 and GMST: USNO Circular       |
|                  | No. 163 (IAU Resolution)                               |
|                  |--------------------------------------------------------| 
|                  | A priori ERP values taken from IGS Rapid Service Bull. |
----------------------------------------------------------------------------- 

REFERENCES:

  Fliegel, H., T. Gallini and E. Swift (1992), Global Positioning System 
    radiation force model for geodetic applications, J.Geophys.Res. 97(B1), 
    pp. 559-568, January 1992.

  McCarthy, D.D. (ed.) (1992). IERS Standards (1992), IERS Technical Note 
    13, Observatoire de Paris, July 1992.

  Melchion, P (1978), "The Tides of the Planet Earth", Pergamon Press,
    pp. 109-121.

  Remondi, B.W., Extending the National Geodetic Survey Standard GPS Orbit
    Formats, NOAA Technical Report 133 NGS 46, Rockville, MD, November 1989.

  Remondi, B.W., NGS Second Generation ASCII and Binary Orbit Formats and
    Associated Interpolation Studies, Proceedings Twentieth General Assembly
    of the International Union of Geodesy and Geophysics, Vienna, Austria,
    August 1991.

  Schenewerk, M.S., MacKay, J.R., Kass, W., Miranda, C., and Mader, G., (1993),
    Rapid Turnaround GPS Ephemerides from the National Geodetic Survey,
    Proceedings of the ION GPS-93, Institute of Navigation, pp. 247-255.

[Mailed From: Mark Schenewerk <[email-masked]>]