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Technical note

Notes for the advanced reader:

  • Weather satellites are equipped with sensors for detecting visible lights and infrared (IR) radiation using different channels in the electromagnetic spectrum. The capability to detect IR radiation enables 'night vision', i.e. 24 - hour operation. A listing of the different channels is given below:

NOAA / FY-1* channels and wavelengths

MTSAT/FY-2 # channels and wavelengths

1: 0.58 - 0.68 um
( visible / yellow )

VIS: 0.55 - 0.90 um
( visible )

2: 0.725 - 1.0 um
( near IR )

3A: 1.58 - 1.64 um
( short wave IR )

-

3B: 3.55 - 3.93 um
( intermediate IR )

IR4:3.5 - 4.0 um
( intermediate IR )

-

IR3: 6.5 - 7.0 um
( intermediate IR )

4:10.3 - 11.3
( thermal IR )

IR1:10.3 - 11.3
( thermal IR )

5:11.5 - 12.5 um
( thermal IR )

IR2:11.5 - 12.5 um
( thermal IR )

*FY-1 channels somewhat differ from those of NOAA satellites in that FY-1 covers only the range 0.84um - 0.89um for channel 2 . There are also additional channels for other applications.
# FY-2 series satellite covers the range 6.3um 7.6um for IR3 channel.

  • The multi-observational channels have enabled certain invisible features (e.g. IR emitted from hot objects) to be captured. During image processing, a colour (e.g. Red) is assigned to a certain channel and other colours (Green and Blue) are assigned to other channels. The combined image would then make certain invisible or vague features distinguishable.