Simple Ratio

This is the simplest VI which is a ratio between the reflectance recorded in the Near Infra-Red (NIR) and Red bands. This is a quick way to distinguish green leaves from other objects in the scene and estimate the relative biomass present in the image. Also, this value may be very useful in distinguishing stressed vegetation from non-stressed areas.

                                                              

According to the spectral signature of green leaves, they exhibit very low reflectance in the Red and Blue regions (leaves reflect more in the green region and hence appear green). However, the reflectance is relatively higher in the NIR region. Thus, the SR value is close to 1 when the object has similar reflectance in both Red and NIR bands – for example, soil. Whereas, for a green object the value would be much greater than 1.