Step 3: Pre-Process the Images as Needed

MSG IR 10.8 µm image 03 Mar 2004 1212 UTC before being stretched in the process of creating a dust RGB product

Before combining these channels into an RGB, the input images need to be processed to better highlight features of interest.

The first image, the 10.8 µm infrared channel, needs what is called contrast stretching.

Conceptual depiction of IR dust detection by contrast with the surface during the daytime

To understand why, consider how the channel detects dust layers aloft. The radiating temperature of the surface is greater than that of the dust aloft, therefore the dust stands out against the hotter background.

Conceptual depiction of IR dust detection by contrast with the surface at night

But the contrast is often limited. For example, at night, the temperatures of the dust and background surface are similar.

Enhancement table with a portion stretched for use in creating a dust RGB

To make the most out of the limited contrast and really highlight the dust features, we stretch the temperatures within a relatively narrow temperature range, as shown in the chart. The warm cutoff is 289 Kelvin (the white in the image), and the cold cutoff is 261 Kelvin (the black in the image).

MSG IR 10.8 µm image 03 Mar 2004 1212 UTC after being stretched in the process of creating a dust RGB product

The resulting image usually enhances the dust signature and provides useful information when combined with the other inputs into the RGB.