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I'm really happy to find this website. It is very helpful for the learners of Arcgis. Now I wanna ask a question. When i open NDVI image in ENVI, its value is still within the range (-1 to 1). But when I open this NDVI image in ERDAS and Arcgis, its value is 0-255. What does it mean? Is the NDVI image some problem? best regards |
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NDVI ranges from (theoretically) -1.0 to +1.0. If you got data ranging from 0..255 then you have data to 8 bit integer which need to be correctly rescaled to -1.0..+1.0 based on the related metadata. |
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What method did you use to generate this NDVI? It may be that ArcGIS and ERDAS make a normalization of their data by comparing the range of -1 to 1 for 0 to 255 so that its value to become integer and not floating. But you must know how NDVI was generated. a hug. |
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The VI Calculator by default applies a biophysical mask to values that are unreasonable. It is likely that the atmospherically corrected data has some values that are outside a reasonable range (because some pixels are not modelled well) and thus return unreasonable NDVI values. These should be masked. |
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