I'm trying to calculate NDVI from Landsat 5 imagery. I'm using ArcMap 10.2.2. I know that the formula for NDVI is (VIS-INFRA)/(VIS+INFRA), where in Landsat 5 VIS= band 3 and INFRA= band 4.
When I plug this into the raster calculator I get a raster with a max of 0.8, a min of -0.4 and a std of 0.1.
The NDVI tool in the Image Analysis window seems convenient (and would save a minute or two for each calculation if it worked properly), so I tried using that as well. I included a picture of how I'm using the image analysis window. I first designate the correct bands in the options menu, then highlight the proper bands and click on the NDVI button.
The raster I get from this tool has a max 0.98 a min of -0.98 and a std of 0.18. This histograms of both NDVI rasters look completely different.
Am I using the image analysis tool incorrectly? Or which approach in this case would give me the true NDVI values? I am leaning towards the NDVI values I calculated using the raster calculator as being correct, since an NDVI of 0.98 seems unreasonably high for my study area (urban).
Perplexingly, when I use the identify tool and pick any random location, I get the same NDVI value to six decimal places for both rasters. I'm not sure how that can be, yet to have the NDVI raster made through Image Analysis report a min, max, and std very different from the other raster.
Has anyone else run into a similar situation?