I am trying to derive Enhanced Vegetation Index (EVI) from Landsat 5 TM data using ERDAS model builder.d I can't seem to get the output I want as it comes out blank.
This is the formula that I used:
2.5 * (("%Band 4%" - "%Band 3%") / ("%Band 4%" + 6 * "%Band 3%" - 7.5 *"%Band 1%" + 1))
can someone assist me with the exact formula I need to type into ERDAS model builder?
Does anyone see something in here that doesn't make sense — or even better — a formula I could copy/paste?
Best Answer
Your problem is likely due to how your model handles bit-depth. EVI, like NDVI, ranges from -1 to 1 and has a practical range of 0 - 1. Therefore, if you try and perform the EVI (or NDVI) calculation and save it as an integer type raster (e.g. signed 8 bit), the output will appear to be black, or all one value. Rather, you need to save the output as a float type, which allows decimals. Alternatively, you can stretch the data to the full range of, for example, an 8-bit unsigned raster (0 - 256).