AVHRR 1KM Global Scaling

Theoretical description

Implemented algorithm


AVHRR Global Scaling (THEORETICAL METHOD)

  1. Equations for scaling and unscaling values.
           scaled = (actual + shift) * scale + offset
           actual = (scaled - offset) / scale - shift
    

    The tables below reflect the above equations. However, for the sake of efficiency, these equations are not actually implemented in the scaling code. In the scaling code, the "scale", "offset", and "shift" parameters are combined into just a "scale" and "offset" parameter. See the AVHRR Global Scaling (IMPLEMENTED METHOD) table for more details.

  2. Values to be scaled are stored in signed data types, except unsigned byte.
  3. Each value to be scaled must be greater than or equal to 0. This allows the values 0 thru 9 to be reserved for special masks (water, interrupted area,no data, ect). To accomplishthis, a shift value is added to each pixel prior to scaling.
  4. Care must be taken when unscaling the data. The mask values must be reset to some value not present in the data range or they must be reset to a fixed value. For example, if all mask values are set to zero, they will be indistinguishable from a data value of zero.
  5. Satellite zenith angles are truncated to the range -90 to 90.
  6. NDVI values are not actually implemented in the scaling coding and are listed in the these tables only for reference.

    Field Actual Shift Shifted ---------------------------------------------- SatZen: -180 to 180 90 0 to 180 SolZen: 0 to 180 0 0 to 180 RelAz: -180 to 180 180 0 to 360 Reflectance: 0 to 100 0 0 to 100 Radiance: 0 to 540 0 0 to 540 Thermal: 160 to 340 -160 0 to 180 NDVI: -1 to 1 1 0 to 2 | BYTE | 10BIT Field | scale offset min/max Field | scale offset min/max ------------------------------------ ------------------------------------- SatZen: | 1.0 10.0 10/190 SatZen: | 1.0 10.0 10/190 SolZen: | 1.0 10.0 10/190 SolZen: | 1.0 10.0 10/190 RelAz: | 0.5 10.0 10/190 RelAz: | 1.0 10.0 10/370 Reflectance: | 1.0 10.0 10/110 Reflectance: | 10.0 10.0 10/1010 Radiance: | 0.454 10.0 10/255 Radiance: | 1.874 10.0 10/1022 Thermal: | 1.359 10.0 10/255 Thermal: | 5.602 10.0 10/1018 NDVI: | 100.0 10.0 10/210 NDVI: | 100.0 10.0 10/210 | 16BIT | 32BIT Field | scale offset min/max Field | scale offset min/max ------------------------------------- ------------------------------------ SatZen: | 10.0 10.0 10/1810 SatZen: | 100.0 10.0 10/18010 SolZen: | 10.0 10.0 10/1810 SolZen: | 100.0 10.0 10/18010 RelAz: | 10.0 10.0 10/3610 RelAz: | 100.0 10.0 10/36010 Reflectance: | 10.0 10.0 10/1010 Reflectance: | 100.0 10.0 10/10010 Radiance: | 10.0 10.0 10/5410 Radiance: | 100.0 10.0 10/54010 Thermal: | 10.0 10.0 10/1810 Thermal: | 100.0 10.0 10/18010 NDVI: | 100.0 10.0 10/210 NDVI: | 100.0 10.0 10/210 | REAL Field | scale offset min/max ------------------------------------ SatZen: | 1.0 10.0 10/190 SolZen: | 1.0 10.0 10/190 RelAz: | 1.0 10.0 10/370 Reflectance: | 1.0 10.0 10/110 Radiance: | 1.0 10.0 10/550 Thermal: | 1.0 10.0 10/190 NDVI: | 100.0 10.0 10/210


AVHRR Global Scaling (IMPLEMENTED METHOD)

  1. Equations for scaling and unscaling values.
           scaled = (actual * scale) + offset
           actual = (scaled - offset) * unscale
       
           where:
    
           unscale = 1.0 / scale
    
    The tables below reflect the above equations. However, the above equations were derived from the more explicit equations:
           scaled = (actual + shift) * scale + offset
           actual = (scaled - offset) / scale - shift
    
    For the sake of efficiency, the "scale", "offset", and "shift" parameters were combined into just a "scale" and "offset" parameter. This more efficient set of equations are what is actually implemented in the scaling code. See the AVHRR Global Scaling ( THEORETICAL METHOD) table for more details.
  2. NDVI values are not actually implemented in the scaling coding and are listed in the these tables only for reference.
    
                         Field        Actual         Used
                     ---------------------------------------- 
                     SatZen:       -180 to 180    -90 to  90                       
                     SolZen:          0 to 180      0 to 180                 
                     RelAz:        -180 to 180   -180 to 180                    
                     Reflectance:     0 to 100      0 to 100              
                     Radiance:        0 to 540      0 to 540              
                     Thermal:       160 to 340    160 to 340                  
                     NDVI:           -1 to   1     -1 to   1              
    
    
    
                 |         BYTE                          |         10BIT
        Field    |  scale offset min/max        Field    |  scale offset min/max
    ------------------------------------    ------------------------------------
    SatZen:      |    1.0  100.0  10/190    SatZen:      |  1.0    100.0  10/190
    SolZen:      |    1.0   10.0  10/190    SolZen:      |  1.0     10.0  10/190
    RelAz:       |    0.5  100.0  10/190    RelAz:       |  1.0    190.0  10/370
    Reflectance: |    1.0   10.0  10/110    Reflectance: | 10.0     10.0  10/1010
    Radiance:    |  0.454   10.0  10/255    Radiance:    |  1.874   10.0  10/1022
    Thermal:     |  1.359 -207.44 10/255    Thermal:     |  5.602 -886.32 10/1018
    NDVI:        |100.0    110.0  10/210    NDVI:        |100.0    110.0  10/210
    
    
    
                 |         16BIT                          |         32BIT           
        Field    |  scale offset min/max        Field    |  scale offset min/max   
    ------------------------------------     ------------------------------------
    SatZen:      |   10.0   910.0  10/1810   SatZen:      |  100.0   9010.0 10/18010
    SolZen:      |   10.0    10.0  10/1810   SolZen:      |  100.0     10.0 10/18010
    RelAz:       |   10.0  1810.0  10/3610   RelAz:       |  100.0  18010.0 10/36010
    Reflectance: |   10.0    10.0  10/1010   Reflectance: |  100.0     10.0 10/10010
    Radiance:    |   10.0    10.0  10/5410   Radiance:    |  100.0     10.0 10/54010
    Thermal:     |   10.0 -1590.0  10/1810   Thermal:     |  100.0 -15990.0 10/18010
    NDVI:        |  100.0   110.0  10/210    NDVI:        |  100.0    110.0 10/210
    
    
    
                 |         REAL 
        Field    |  scale offset min/max
    ------------------------------------
    SatZen:      |    1.0   100.0 10/190
    SolZen:      |    1.0    10.0 10/190
    RelAz:       |    1.0   190.0 10/370
    Reflectance: |    1.0    10.0 10/110
    Radiance:    |    1.0    10.0 10/550
    Thermal:     |    1.0  -150.0 10/190
    NDVI:        |  100.0   110.0 10/210