The channels have different spatial resolutions: ~1km in the visible, ~5km in the infrared, and ~5km in the water vapor channel. This means that the high resolution information in the compound image is derived from data in the visible channel, while that information having its origin higher in the atmosphere (the water vapor channel) lacks spatial resolution.
The histogram was based on the following limiting ranges:
| Channel Name--Number | Wavelength range | Spatial Resolution | Minimum (unit) | Maximum (unit) |
|---|---|---|---|---|
| Visible -- 1 | 0.49-0.81um | 1 km | 0% (Albedo) | 60% (Albedo) |
| Moisture -- 3 | 6.2-7.1um | 5 km | -77° C | -3° C |
| Longwave -- 4 | 10.1-11.6um | 5 km | -77° C | 38° C |
This image displays the actual histogram used to map a channel's value to a color. The red line is channel 1, the green line is channel 3 and the blue line is channel 4. The data are scaled to be between 0 and 255, after being scaled, the direct-color images are written to 24-bit jpeg file format.
This results in the following colormaps:
Since these images do not substitute any pseudo visible channel data at night, the interpretation of the colors is quite different between day-time and night-time.
| Colors | Characteristics | Interpretation |
|---|---|---|
| White | cold, bright clouds | high cloud top |
| Red | bright cloud that is relatively warm | low cloud top |
| Pinks and purples | Bright and low to intermediate temperature | can sometimes be associated with snow cover, but is difficult to distinguish from low clouds |
| Dark blue/green | dark and warm | clear dark surface |
| Bright green | dark, warm, and high humidity | Clear sky with high water vapor burden |
| Colors | Characteristics | Interpretation |
|---|---|---|
| Bluish white | Cold | High clouds |
| Dark blue | Warm, low humidity | Surface |
| Green | Warm, High humidity | Surface with humidity |
Rao, Holmes, Anderson, Winston, Lehr, Weather satellites: Systems, data and environmental applications.