6. Spectral Ratioing

Spectral Ratioing is used to further highlight differences between features and often reduces the effect of different light reflectance intensities. Spectral ratioing can be used to detect stressed or diseased crops. One common ratio, called Normalized Difference Vegetation Index (NDVI) is: (NIR-RED) / (NIR+RED) or simplified (NIR /RED). For a good video (last accessed 5.19.20 ) explaining NDVI click here. To perform this spectral ratio:

1. Open MultiSpec©.
2. Click File. Click Open Image. Select the file you want to ratio.
3. Select Processor.
4. Select Reformat.
5. Select Change Image File Format.
6. Select Transform Data.
7. Select New Channel from General Algebraic Transformation.
8. Type in your ratio equation. It may be set for NDVI for Landsat 8 data:

= 0.0 + [(1.0 C5 - 1.0C4) / (1.0C4 + 1.0C5)] + 1.0

1. Click OK.
2. Click OK in next window.
3. Save image as a .tif file with a new name, such as the ratio name, NDVI, followed by the existing name .
4. Close initial file and open newly saved file.
5. Select: Display type 1-channel thematic. Click OK twice. Save.
6. Zoom in and re-center as needed.
7. To conduct a classification, go to "Classifying An Image"