The ratio between two bands can help to reveal relationships and remove the effects of differential lighting. Lighting can vary with the seasons, time of day, cloud conditions, or shadows so that absolute reflectances can give misleading results. A low reflectance could be due to a low albedo, low light, or shadows, and otherwise identical pixels would look very different.
The ratio between bands should give a more consistent relationship to the surface materials. Even in shadow, the ratio of reflectance should be similar to the case in bright sun.
On the Imagery analysis menu, Create difference index, band ratio, new band for satellite imagery.
|TM band 3 (red). Note the difficulty in picking out the shoreline.
This is the red ban; the blue band is even worse.
|TM band 4 (NIR) over Band 3 (red): note the sharp differentiation between land and
Normalized satellite indexes
Last revision 9/9/2020