Formula for Enhanced Vegetation Index (EVI) in Raster Calculator?

[StephenChignell]

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:

http://en.wikipedia.org/wiki/Enhanced_vegetation_index


The output should be a raster with values ranging from -1 to 1, but I get values from like 30-40 which is incorrect.

Right now my formula looks like this:


2.5 * (Float("%Band 4%" - "%Band 3%") / Float("%Band 4%" + 6 * "%Band 3%" - 7.5 *"%Band 1%" + 1))


Does anyone see something in here that doesn't make sense-- or even better--a formula I could copy/paste?

Thanks!

[SalmanAhmed3]

Can you tell me what is the purpose of this scale factor? Ive calculated NDVI from Landsat TM and never applied this scale factor. Ive always got the correct values nevertheless. Thats why Im a bit confused why to use this?

[Luke_Pinner]

The EVI formula only works with reflectance (from 0 - 1) because of the coefficients in the formula -  L=1, C1 = 6, C2 = 7.5, and G (gain factor) = 2.5

NDVI has no such coefficients, so you can calculate it regardless of whether your data is scaled or not.

Note that that scale factor I referred to is specifically for the MODIS MYD09A1 surface reflectance product.  MODIS MYD09A1 surface reflectance values are multiplied by 1000 and then stored as 16-bit integer data to reduce file size/storage space.  The scale factor converts the 16 bit values to floating point values from 0.0 - 1.0

If you want Landsat EVI, you can just download it these days. If you want to calculate it yourself, you need to use reflectance data (not DN) which you can either download (the surface reflectance product) or calculate it yourself (either simple top of atmosphere reflectance  or atmospheric correction to surface reflectance).

[MeganMcSherry]

Are you applying the MYD09A1 scale factor of 0.0001?

2.5 * (("%Band 4%" * 0.0001 - "%Band 3%" * 0.0001)) / (("%Band 4%" * 0.0001) + 6 * ("%Band 3%" * 0.0001) - 7.5 * ("%Band 1%" * 0.0001) + 1))

No I hadn't been...the numbers make so much more sense now! Thank you for bringing that to my attention, I'm still learning. Much appreciated.

[ahmedzaeen1]

Please, I tired to do it, but unfortunately, I have got  map has the same color. just one color?????

[RushatiDey]

Hello, could you calculate the EVI values? I'm facing the same issue. Even after ToA correction,the values are not between -1 to +1.