Infrared Satellite Image
Infrared (IR) images are derived from radiation emitted from the Earth and its atmosphere at thermal-infrared wavelengths (10-12 µm). These images provide information on the temperature of the underlying surface or cloud. IR images are available 24 hours per day because temperature can always be measured.
Temperatures are represented by a greyscale, where black and white represent the hottest and coldest areas respectively. As clouds tend to be cooler than the ground or sea below (not always the case for low-lying clouds), they appear as light grey to white.
Himawari-8 is a geostationary satellite operated by the Japan Meteorological Agency and is permanently stationed over the equator at a height of approximately 35,800 km near 140° E. This satellite provides excellent coverage over the Australian region and is the basis for images used by the Australian Bureau of Meteorology.
The image above is known as a cloud/surface composite, and is enhanced to clearly show land areas. These types of images are created by combining information from two images:
- The Earth’s surface (land and oceans) is a static image from NASA's Blue Marble image set.
- The cloud cover, which is overlaid on top of this surface image, is derived from a greyscale infrared image by removing the temperature range associated with the surface.
While a clouds/surface composite gives a good indication of the current cloud cover, it should not be confused with a true visible image.
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