USGS EROS Archive - Advanced Very High Resolution Radiometer (AVHRR) - 1KM Global Scaling Active

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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. 

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.

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 Field | scale offset min/max 

• SatZen: | 1.0 10.0 10/190
• SolZen: | 1.0 10.0 10/190
• RelAz: | 0.5 10.0 10/190
• Reflectance: | 1.0 10.0 10/110
• Radiance: | 0.454 10.0 10/255
• Thermal: | 1.359 10.0 10/255
• NDVI: | 100.0 10.0 10/210

10BIT 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: | 10.0 10.0 10/1010 
• Radiance: | 1.874 10.0 10/1022 
• Thermal: | 5.602 10.0 10/1018 
• NDVI: | 100.0 10.0 10/210

16BIT Field | scale offset min/max 

• SatZen: | 10.0 10.0 10/1810
• SolZen: | 10.0 10.0 10/1810
• RelAz: | 10.0 10.0 10/3610
• Reflectance: | 10.0 10.0 10/1010
• Radiance: | 10.0 10.0 10/5410
• Thermal: | 10.0 10.0 10/1810
• NDVI: | 100.0 10.0 10/210 

32BIT Field | scale offset min/max 

• SatZen: | 100.0 10.0 10/18010 
• SolZen: | 100.0 10.0 10/18010 
• RelAz: | 100.0 10.0 10/36010 
• Reflectance: | 100.0 10.0 10/10010 
• Radiance: | 100.0 10.0 10/54010 
• Thermal: | 100.0 10.0 10/18010 
• 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. 

   1. 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

Additional Information

• Advanced Very High Resolution Radiometer (AVHRR) 

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