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I need to get MODIS NDVI (MOD13A3), but output from EarthExplorer or Daac2Disk HDF format is a numerical range is -2000 to 9996.

But I need for futher work basic range -1 to 1.

Is there any conversion method?

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The product description page says the following:

Science Data Sets

  • (HDF Layers) (11): 1km monthly NDVI
  • UNITS: NDVI
  • BIT: 16-bit
  • TYPE: signed integer
  • FILL: -3000
  • VALID RANGE: -2000, 10000
  • MULTIPLY BY SCALE FACTOR: 0.0001

My first guess would be to multiply your data with 0.0001 to get to the correct NDVI values. You could use an additional conditional statement to set -3000 values to nan/nodata

UPDATE: I guess in your case the fill value might not be set

UPDATE2: Here is the description (p. 5)

"MOD13A3 product
As presented in Table 2, the NDVI value given in MOD13A3 products is a integer (16 bits) and range between -2000 and 10 000. In order to convert these values in NDVI “true” values was necessary to apply a scale factor. Therefore, all the original data were multiplied by 0.0001 and the final values were in the range between -0.2 and 1.0. "

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