The NDVI (Normalized Difference Vegetation Index) tool in the Image Analysis Window calculates how vigorous the vegetation is in an area. But it’s not the only index available, although it may be the most widely used.
When indices have the same format as NDVI, which is to say (Band X – Band Y)/(Band X + Band Y) you can substitute any of the bands and the tool will still work. For example, to calculate the Normalized Difference Built-up Index (NDBI), select the near infrared and the shortwave infrared bands. For Landsat 7, band 4 is near infrared and band 5 is shortwave infrared. For Landsat 8, band 5 and 6 showed the most contrast (in a limited observation of Landsat 8 here at Redlands). Choose the appropriate bands and click the NDVI button, and your output will be the NDBI. NDBI is great for showing impervious surfaces and is really useful for detecting the growth of cities.
The reason this works is because the NDVI tool is programmed; see last week’s blog for more background on what the tool is doing. Urban areas are the lighter blues, green is forest, and the deep blues are water. Here’s what the NDBI looks like—can you guess what city this is?
Written by Kevin J Butler