A flight is due to depart from Heathrow (EGLL) at 00:15 local time. The pilot wishes to watch satellite imagery to determine the weather situation on the route. Which type of imagery should be used?
SATELLITE IMAGERY
Cloud detection.
There are two methods of producing the weather picture; visual photography and infrared.
- Visible imagery is produced by the sun's rays reflecting off of clouds - which means that it is not available continuously, due to the lack of sunlight at night. Clouds will appear white, the land grey and the sea black.
- Infrared imagery is produced by sensing the emitted radiation coming off of clouds. The temperature of the cloud will determine the wavelength of radiation emitted from the cloud. Infrared images have the advantage of being available for 24 hours a day and the shading of the picture will be more or less the same by day and by night. Cold (high) cloud will give a white image, lower cloud a somewhat darker one, whilst warm land will give a dark image.
With regards to this question, note that this is a night flight. As above discussed, at night, due to lack of sunlight, visible images are not available. Therefore, the weather picture which shall be used is the infrared imagery, which is available 24 h a day.
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