From July 2015, the Bureau of Meteorology has been receiving satellite observations data from Himawari-8, a geostationary satellite operated by the Japan Meteorological Agency (JMA). Himawari-8 and its sister satellite, Himawari-9, are the successors to JMA’s Multi-functional Transport Satellites (MTSAT), and offer significant improvements in frequency, resolution and precision. They are situated 35 800 km above the equator at longitude 140.7°E (above the western Pacific, in line with Japan, Papua and central Australia) and so provide excellent coverage of the Australian region.
Himawari-8 data are used extensively within the Bureau to assist in real-time analysis and forecasting, and are also fed into the Bureau's numerical weather prediction (NWP) models.
The Bureau also receives data from China's Feng Yun-2 series of geostationary satellites, which are situated over the equator at longitudes of 86.5°E and 105°E, providing excellent coverage of the Indian Ocean and the western parts of Australia.
Our Crib Point Satellite Earth Station is the only dedicated weather-related Satellite Earth Station in Australia, forming a critical part of the Bureau's operations.
The following types of imagery are available to the public:
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 temperatures can always be measured. This is in contrast to visible images, which are only available during daylight hours.
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, making IR images simple to compare with visible images.
To assist in interpreting greyscale IR images, methods can be used to colour all pixels representing a particular temperature range. The temperature of clouds is associated with their height, so highlighting certain temperature ranges is useful for estimating the height of the observed clouds. These precision of these temperature measurements are within one or two degrees Celsius. Images coloured in this way are known as 'false colour' images.
The Bureau also provides false colour infrared images that use the Zehr colour enhancement, which was developed by Ray Zehr from the US National Oceanic and Atmospheric Administration (NOAA). This enhancement only applies temperature colour ranges to the cold end of the scale, which highlights very deep convection that is generally associated with tropical cyclones and thunderstorms. Hence, this type of image can be useful in tracking the movement of tropical cyclones.
Visible (VIS) images are a record of the visible light scattered or reflected towards the satellite from the Earth and clouds. They give meteorologists extra information that may not appear on infrared images. For example, fog appears in visible images, but may not show up in infrared images as its temperature is very close to that of the land below.
Visible images are only available during daytime, as at night there is no reflected sunlight.
The clouds/surface composites 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 (see Infrared Images), 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.
Daytime visible / night-time infrared blended imagery
Observations from Himawari-8 enable the Bureau to create true colour visible imagery during the day. To avoid this imagery fading to black at night, the daytime visible / night-time infrared blended imagery provides an easy to use product, which essentially incorporate the best available data for any particular time of the day.
Image updates and timestamps
Satellite images are timestamped in 'UTC' (Coordinated Universal Time). The timestamp is the start time of the observation of the top of the image from the satellite. It takes approximately ten minutes for Himawari-8 to complete a scan.
As geostationary satellites orbit the Earth, there are certain times during the year when the Earth is directly between the Sun and the satellites. This results in the Earth eclipsing the satellites. Such eclipses occur each year, usually between February to April and between August and October.
In these circumstances, the Sun can shine directly into the optical path of the satellites' instrumentation, overloading the sensors. The observing instrument is shielded to avoid this 'flaring', so a whole image or parts of an image may be missed.