How to create Night Microphysics RGB images

EUMETSAT's recommendation for Microphysics RGBs is that the cloud thickness information should be visualized in red, the microphysical information in green, and the temperature information in blue.

The 'recipe' of the Night Microphysics RGB type is summarized in Table 1. It shows which channels correspond to which color. The measured values should be calibrated to brightness temperatures. The images should be then enhanced - linearly stretched - within the ranges shown in the table.

AVHRR Night Microphysics RGB
Color Channel Range
Red IR12.0 - IR10.8 -4 +2 K
Green IR10.8 - IR3.74 -4 +6 K
Blue IR10.8 243 293 K

Table 2:Recipe of the AVHRR Night Microphysics RGB scheme

The following example shows how the Night Microphysics RGB is combined from IR3.74, IR10.8 and IR12.0 images. Both the resulting RGB and its components are included.

Fig. 2a shows the three IR channels separately as single channels, all enhanced in the 243-293 K brightness temperature range. Usually the IR images are grayscale images in which bright shades are assigned to cold and dark shades to warm objects. However, in Fig. 2a the warm objects (surface, warm clouds) are bright and the cold clouds are dark. In Fig. 2a the Po Valley and several other areas are covered by fog or low clouds. This fog is not (or barely) visible in the IR10.8 and IR12.0 images. In the IR3.74 image one might suspect its presence. As mentioned before, the transparency of cirrus clouds is dependent on wavelength; see for example the thin cirrus clouds over the ocean west of France. They are the least dark (the most transparent) in the IR3.74 image.

Figure 2a: AVHRR IR3.74 (top), IR10.8 (middle) and IR12.0 (bottom) images of western Europe on 10 December 2015 at 03:18 UTC

Fig. 2b shows the color components of a Night Microphysics RGB image; that is, the channel (differences) found in the recipe with the corresponding enhancement. The lower left panel shows the Night Microphysics RGB.

  • In the (IR12-IR10.8) difference image semi-transparent clouds in their dark shades are easily recognizable, while fog is not.
  • In the (IR10.8-IR3.74) difference image the surface is medium grey, water clouds (fog) are much brighter, while thin ice clouds are dark. Foggy areas have excellent contrast against cloud-free areas.

Figure 2b: AVHRR (IR12.0-IR10.8) BTD (upper left), (IR10.8-IR3.74) BTD (upper right), Night Microphysics RGB (bottom left) and IR10.8 (bottom right) images of western Europe on 10 December 2015 at 03:18 UTC

Fig. 2c shows the same images as Fig. 2b except the three components are visualized in their respective colors instead of shades of gray. This is how the three components are visualized together in the RGB.

Figure 2c: AVHRR (IR12.0-IR10.8) BTD (upper left), (IR10.8-IR3.74) BTD (upper right), Night Microphysics RGB (bottom left) and IR10.8 (bottom right) images of western Europe on 10 December 2015 at 03:18 UTC

Fig. 2d shows the four panels of Fig. 2b on top of each other. Hover your mouse over the image to use the slider.

12.0-10.8 10.8-3.7 10.8 night micro
12.0-10.8

Figure 2d: 4-Panel display, please use your mouse to compare the four images. AVHRR (IR12.0-IR10.8), (IR10.8-IR3.74), IR10.8 and Night Microphysics RGB images of western Europe on 10 December 2015 at 03:18 UTC.