ENVI Vegetation Index Calculator

Question

I am attempting to input 4-band CIR imagery into ENVI's Vegetation Index Calculator and keep running into the same error: "Wavelengths must be defined to calculate vegetation indices".

I have attempted the following troubleshooting based on this thread with no success:

File > Edit ENVI Header > Edit Attributes > Wavelengths... > Wavelength/FWHM Units: Wavenumber

Unfortunately ENVI's help section does not provide good support for this problem. Any advice on how to correctly input these images would be greatly appreciated.

Edit: An example of the 2010 NAIP 1M NC/CIR DOQQ input imagery can be found here. Please note that I converted the base DOQQs from .jp2 to 8 bit unsigned geoTIFFs.

Answer 1

Assuming this is just a follow on to your previous question about vegetation indices, I would recommend not using the Vegetation Index Calculator. It's quite cumbersome, and (as far as I can tell) more relevant for hyperspectral imagery where you want ENVI to automatically choose the correct band from an image cube based on that wavelengths defined in the header.

Instead, I would suggest using the Band Math tool. If you're doing NDVI or EVI, you can just type in the formula here, choose the bands, and ENVI will run the calculation. You will want to have your EVI formula be something like this:

2.5 * ((B2-B1) / (B2 + 6 * B1 - 7.5 * B3 + 1))

Where B1 = red, B2 = NIR, and B3 = blue. Note that you may need to play around with the float() command depending on the data type of the NAIP data. Otherwise, ENVI will incur some serious rounding errors.