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AVHRR 1KM Global Scaling

~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

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   U.S. Department of the Interior | U.S. Geological Survey URL: http://edcsns17.usgs.gov/1KM/scale_1km.html Page Contact Information: custserv@usgs.gov Page Last Modified: Friday August 19, 2005

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