Satellite imagery on this site is obtained from geostationary meteorological satellites. Geostationary meteorological satellites maintain a fixed position relative to the earth. They are positioned about 36,000 km above the equator and complete one orbit every 24 hours.

Infra-red Images

Infra-red (IR) images are the result of the satellite sampling the infra-red (long-wave) radiation which upwells from the earth's surface and atmosphere. The images show the temperature of the radiating surface - that is, the temperature of land, sea or cloud top. The NZ-Tasman and Australian animated images depict the sea and land surfaces as false-coloured blue and green respectively. Because infra-red radiation is emitted by cloud tops and the earth's surface continuously, infra-red images are available at any time of the night or day. The public can reasonably interpret the following from the IR satellite imagery shown here:

• A sequence of IR satellite images may illustrate the development of cloud masses associated with significant weather features such as depressions and fronts;
• Because the higher atmosphere is colder, the whiter the IR cloud image, the higher the cloud tops. Low cloud tops are represented by grey colours. Very low cloud (for example, fog), will emit a similar IR signal to the underlying land or sea and may be hard to distinguish.
• The influence of New Zealand's terrain on air flow, and consequently on cloud shape, varies from situation to situation. Mountain chains may block the air flow, causing a build-up of cloud on the windward side and a depletion of cloud from the leeward side. However, in some situations wave ("lenticular") clouds will also form on the leeward side of the mountain chain, but at a higher level, and therefore appear a brighter white in the IR image.
• Concentrations of small speckled clouds can often indicate cold showery airflow. These can sometimes be seen moving northwards from the Southern Ocean.
• The centre of low pressure systems can sometimes be seen as clockwise "whirls" of cloud;
• Cloud movement gives some indication of wind speed and direction at cloud height, which may be different to the winds experienced at ground or surface level.

Satellite images will show areas of cloud but will not show rainfall. On the other hand, radar shows areas of rainfall but tends not to detect cloud that is free of precipitation.