NOAA GFO Altimeter IGDR Format: 11/24/03

  ITEM   PARAMETER           UNITS         RANGE        BYTES  

    1    UTC (since 1/1/85)  sec         2E8 to 5E8         4    
    2    UTC (continued)     micro sec   0 to 1E6           4    
    3    Latitude            micro deg   +/- 72.0E6         4    SLR/Doppler
    4    Longitude           micro deg   0 to 360.0E6       4       ""
    5    Orbit               mm          7.7E8 to 8.1E8     4       ""
    6    Flags               bits        (see below)        4    
    7    H (uncorrected)     cm          +/- 1.5E5          4    
    8    Sigma (H)           cm          0 to 100           2    Linear Fit
    9    SWH                 cm          0 to 2500          2    
   10    Sigma (SWH)         cm          5 to 100           2
   11    AGC                 .01 dB      ??                 2    
   12    Sigma (AGC)         .01 dB      ??                 2    
   13    No. in average                  6-10               2    
   14    Mean Sea Surface    cm          +/- 1.5E5          2    OSUMSS95
   15    Solid Tide          mm          +/- 500            2    T/P (TIDPOT)
   16    Ocean Tide          mm          +/- 5000           2    CSR_3.0
   17    Wet (NCEP)          mm          0 to -400          2    Operational
   18    Dry (NCEP)          mm          -2100 to -2400     2        ""
   19    Iono                mm          0 to -200          2    IRI95
   20    ATT_SWH correction  mm          ??                 2    
   21    Sigma-0             .01 dB      0 to 4000          2    
   22    Attitude**2         1e-4 deg**2 ??                 2    ** 11/24/2003
   23    SDR Status Word #1  bits                           2    
   24    Wet (NVAP)          mm          0 to -400          2    Climatology
   25    Wet (MWR)           mm          0 to -400          2    Radiometer
                                                                 
                                   TOTAL NUMBER OF BYTES   64      
Notes:

1) Values unavailable for any reason are set to 2147483646 (4 bytes, 2**31 - 2)
   or 32767 (2 bytes, 2**15 - 1).

2) Flag bits:  0:  Set to 1 if over water, based on 1/12th-deg land mask
                   Set to 0 if over land
               1:  Set to 1 if over water > "2251m", based on 1-deg mask
                   Set to 0 if over shallow sea < "2251m", or over land
	       8:  Set to 1 if wet/dry model interp. > 6 hours (06/21/2001)
            2-31:  RA Quality Word #1, bits 2-31, from SDR (bits 0,1,8 = spare)

   Also, field #23 contains flag bits from Status Word #1 (2-byte)

3) H is height above the reference ellipsoid, computed as the difference
   between the orbit (mm) & the altimeter range to the sea surface (cm):

	      H = Orbit/10.0 - Altimeter

   The reference ellipsoid is: ae = 6378136.3 m; f = 1/298.257 (Topex/Poseidon)

   Environmental corrections (mm) are applied to H (cm) as follows:

              H (corrected) = H - 0.1 ( Tides + Wet + Dry + Iono )

   Instrumental corrections have already been applied to the "uncorrected"
   heights in field #7.

4) Field #22 changed from attitude (.01 deg) to attitude squared 
   (.0001 deg**2) on 11/24/03 to avoid clipping from SDR values of
   attitude. Attitude squared is computed from fitted VATT according to the
   formula: att**2 = b1**2 * (VATT_F - b0); b0=1.11, b1=.8747.