About the Satellite Images

Satellite | Satellite Products and Archive | About Satellite Images

Infrared (IR) images

IR images are derived from radiation emitted from the Earth and its atmosphere at thermal-infrared wavelengths (10-12 µm). They provide information on the temperature of the underlying surface or cloud.

IR images are available 24 hours per day because temperatures can always be measured, regardless of day or night. (This is in contrast to Visible images which are only available during the day. See below). The temperatures are represented either by a grey-scale (black is no-cloud, and increasing white means higher colder clouds), or in a colour scheme.

IR imagery is available on:

• NOAA 17 and NOAA-18: Channel 4: 10.3-11.3 µm Channel 5: 11.5-12.5 µm
• MTSAT-1R: Channel 4: 10.3-11.3µm Channel 5: 11.5-12.5 µm
• FY-2C: IR1: 10.5-12.5 µm

• More information on IR images

Visible images

Visible (VIS) images are a record of the visible light scattered or reflected towards the satellite from the Earth and clouds. i.e. you can 'see' the clouds. Visible images give meteorologists extra information that may not appear on Infrared temperature images. For example, fog appears in Visible images, but may not in Infrared images when the fog and the land are at the same temperature.

Visible images are only available during the daytime, because at night the world looks black. VIS images are normally displayed in a manner similar to that seen by the human eye. Using a black and white colour scale, with different shades of grey indicating different levels of reflectivity, the brightest and most reflective surfaces are in white tones and the least reflective in black. In general, clouds are seen as white objects against the darker background of the earth's surface.

Visible imagery is available on:

• NOAA 17 and NOAA-18: Channel 1: 0.58-0.68 µm Channel 2: 0.725-1.10 µm
• MTSAT-1R: Channel 1: 0.55-0.90µm
• FY-2C: VIS 0.5-1.05 µm

• More information on VIS images

Water Vapour channel

Water Vapour imagery is derived from radiation emitted by water vapour at wavelengths around 6-7 µm. This is not an atmospheric window but a part of the spectrum where water vapour is the dominant absorbing gas. The centre of the absorbing band is 6.7µm.

The water vapour channel is available on MTSAT-1R and FY-2C.

• More information on the Water Vapour channel

Image Updates

The time stamp on the images is the start time of the reception of the top of the image from the satellite. It takes approximately 30 minutes for MTSAT-1R to complete a scan and the image is generally available on the Web within 30 minutes of completion, i.e an hour after the time stamp.

Time stamps

Satellite images are time stamped in "UTC" (Coordinated Universal Time), which is equivalent to GMT or Z time (Greenwich Mean Time). This is the start time of the reception of the top of the image from the satellite. It takes approximately 30 minutes for MTSAT-1R to complete a scan and the image is available on the Web within 30 minutes of completion, i.e an hour after the time stamp.

Below is a comparison of current UTC to current Eastern Standard Time (EST), Central Standard Time (CST) and Western Standard Time (WST) or the Daylight Saving equivalent.

To convert UTC times to local Australian times, add the time difference between your Australian time zone and UTC. For daylight saving add an extra hour to the difference between Australian times and UTC. During daylight saving, the difference for (EDT) i.e. New South Wales, Victoria and Tasmania is 11 hours instead of 10, and the difference for South Australia (CDT) is 10.5 hours instead of 9.5, and the difference for Western Australia is 9 hours instead of 8.

• More information on UTC and Daylight Savings Time

Browsing the Archive

A browse service provides free access to browse images for Visible (1:32 resolution) or Infrared (1:8 resolution) channels to assist with the selection of required dates and times for ordering higher resolution images or radiances from the Bureau's Satellite Data Archive.