About The Satellite Pictures
Understanding the Satellite Pictures
On the Bureau's WWW service, there are two types of satellite images: infrared and visible. Visible images are just like those that a normal video camera (black and white) would see looking down at the earth - the brightest clouds are usually the thicker ones low down in the atmosphere and the duller clouds are the thin ones such as cirrus. Infrared (IR) images convert the temperature of the cloud, or land or sea (whichever the satellite can see at each point) to a shade of grey. The warmest points are at the ground and are black. The coolest points are high in the atmosphere (cirrus cloud) and are white. In between are shades of grey which become brighter as the cloud becomes colder (higher). The dull grey cloud which you see on the IR images is low to middle cloud. Sometimes the differences in temperature of the ground can also be seen as different shades of grey.Timestamping
Satellite images are timestamped in "UTC" (Coordinated Universal Time), which is equivalent to GMT (Greenwich Mean Time). To convert these times to local Australian times, add the time difference between your Australian time zone and GMT to these times:- For Eastern States, add 10 hours e.g.
- 0000 UTC = 1000 (10 a.m.) EST
1200 UTC = 2200 (10 p.m.) EST
1800 UTC = 0400 ( 4 a.m.) EST next day - For S.A. and N.T., add 9.5 hours e.g.
- 0000 UTC = 0930 (9.30 a.m.) CST
1200 UTC = 2130 (9.30 p.m.) CST
1800 UTC = 0330 (3.30 a.m.) CST next day - For W.A., add 8 hours e.g.
- 0000 UTC = 0800 (8 a.m.) WST
1200 UTC = 2000 (8 p.m.) WST
1800 UTC = 0200 (2 a.m.) WST next day
The satellite images also have an associated "Z" time. This refers to the nearest UTC hour to which the image is received in full. The image takes about 25 minutes to transmit, starting usually at half past the hour. Thus, the image that is started at 23:32 will be called the 00Z image.
Updating
The free service provides a satellite image every 6 hours, when the image is available.March 1996