Hi everyone, I'm trying to derive Enhanced Vegetation Index (EVI) from Landsat 5 TM data using the raster calculator and I can't seem to get the output I want. Here is a link to the description and formula for EVI:
What data type are the bands? If you have byte or unsigned integer data, you might be getting integer overflows as you're applying the float conversion after the operations. As an example - say you have unsigned 16bit integers, band 4 = 500 and band 43 = 750. Float(500 - 750) will return 65286 but Float(500) - 750 will return -250.0.
I'm trying to derive Enhanced Vegetation Index (EVI) from Landsat 5 TM data using the raster calculator and I can't seem to get the output I want. Here is a link to the description and formula for EVI:
The output should be a raster with values ranging from -1 to 1, but I get values from like 30-40 which is incorrect.
The coefficients you are using are hard-coded for MODIS data sets (as stated in the wikipedia article). Additionally, the values required are not raw Landsat dataset DN values (0-255) but instead must be atmospherically-corrected reflectance values.
The coefficients you are using are hard-coded for MODIS data sets (as stated in the wikipedia article). Additionally, the values required are not raw Landsat dataset DN values (0-255) but instead must be atmospherically-corrected reflectance values.
Hi Curt, Thanks for the advice--I do plan on using atmospherically corrected imagery in my eventual run--I forgot to mention that.
Thanks too for the article, it was very informative. However, do you know if EVI correction factors have been developed for TM data? I can't seem to find anything that suggests anyone has derived EVI from Landsat.
What data type are the bands? If you have byte or unsigned integer data, you might be getting integer overflows as you're applying the float conversion after the operations. As an example - say you have unsigned 16bit integers, band 4 = 500 and band 43 = 750. Float(500 - 750) will return 65286 but Float(500) - 750 will return -250.0.
What data type are the bands? If you have byte or unsigned integer data, you might be getting integer overflows as you're applying the float conversion after the operations. As an example - say you have unsigned 16bit integers, band 4 = 500 and band 43 = 750. Float(500 - 750) will return 65286 but Float(500) - 750 will return -250.0.
I am having a similar problem in creating the formula for EVI using MODIS bands. No matter which way I enter it (with the float conversion in various positions), I still get an index from -10405 to 9610. All of the bands I am using are 32-bit unsigned integers. Any tips on how to enter the EVI equation using these MODIS bands?
