Satellite images are images taken from space of an area at any given time. The three types of satellite imagery displayed on Weatherzone are infrared images, visible images and water vapour images.
Visible satellite imagery takes a photo of what the sky (and ground) "look" like at any one time. Therefore, these images are only useful during daylight hours. Thicker cloud will show up as brighter white in these images, regardless of its height. Thin cloud shows up as paler grey shades.
Infra-red satellite imagery detects the temperature of the cloud tops (or ground). As it does not rely on visible light for illumination, these images are available 24 hours a day. Colder temperatures are shown in brighter shades of white and warmer temperatures in darker shades of grey. Therefore, low cloud, which is close to the surface and, as such, warm, will show up very faintly. High cloud, which is colder, will show up as bright white.
Therefore, during daylight hours, it is possible to use visible and infra-red satellite imagery in tandem to get a better snapshot of the state of the atmosphere. Visible imagery can be used to get an idea of the thickness of clouds (and also to detect low cloud that may not have been apparent on infra-red imagery) and infra-red imagery can give an idea of the height of those clouds.
Water vapour images show moisture in the atmosphere that may or may not be in the form of clouds.
11:28 EST Commuters on Sydney Harbour ferries have faced "white knuckle" trips to work this morning, with services still operating as the city is smashed by wild storms.