The Bureau of Meteorology currently runs a computer model which produces estimates of the total amount of solar radiation that reaches the earth's surface in a day called "daily global solar exposure". For each location on the surface of the earth, an energy budget calculation is made using hourly visible radiation information i.e. radiances from the current operational geostationary meteorological satellite.
This process involves calculation of instantaneous downward irradiance (radiative fluxes) at the ground every hour in real time over Australia using the hourly visible satellite data, as well as data on total column water vapour and recent hourly surface albedos. The hourly irradiances are then integrated during each evening to give daily insolation totals in megajoules per square metre, i.e. "daily global solar exposure".
The solar exposure values have been derived for most days since the start of 1990 from a sequence of satellites: GMS-4, GMS-5, GOES-9, MTSAT-1R, MTSAT-2 and, since 23 March 2016, Himawari-8. The satellite model's horizontal resolution is 0.05 degrees in longitude and latitude, or approximately 5 km. The accuracy of the model's daily estimates of insolation is estimated by comparison with independent measurement by Bureau ground instruments.
Solar exposure estimates are important for a wide range of applications, mainly in the agricultural and to a lesser extent engineering sectors, and in research. Examples of use include:
- monitoring plant growth and disease control;
- evaporation and irrigation;
- architecture and building design e.g. power station condensor cooling systems;
- power generation;
- calculation of water requirements for crops;
- solar heating system design and use;
- skin cancer research;
- research into coral growth;
- weather and climate prediction models;
- solar powered car races.
Solar radiation data can potentially be provided in a variety of forms to suit these applications. Currently the satellite-derived data are available as daily colour maps, daily grid files and daily point values for many locations in Australia. The schedule of updates is available here.
Map Projections
The map projections used are either Cylindrical Equidistant (CE) or Lambert Conformal (LC). The Lambert Conformal projection takes three parameters; the central longitude (in degrees east of the Greenwich Meridian) and two standard parallels of latitude (in degrees south of the equator).
| Region | Aus. | Qld | NSW | Vic. | Tas. | SA | WA | NT |
|---|---|---|---|---|---|---|---|---|
| Map projection | LC 134° 10°, 40° | CE | CE | LC 140.8° 10°, 40° | LC 146.5° 10°, 44° | CE | CE | CE |
The Victoria and Tasmania maps are based on a finer resolution analysis than the remaining maps. Consequently there may be slight inconsistencies in the detail represented on the Vic./Tas. maps as compared against the Aus./SA/NSW maps.
Grid format
Daily and monthly solar exposure grids may be downloaded from the Bureau's website. These grids are in an ASCII format suitable for ingesting into geographic information systems (GISs), compressed using the UNIX compress utility. The ASCII grids have appended to them their original AIFS ASCII grid header (a Bureau of Meteorology grid format), to provide additional grid metadata. Note that some GISs may require the user to change the grid file extension from '.grid' to '.txt', prior to ingestion into the GIS.
Outages
Satellite problems occasionally mean that the solar radiation data are not available. During an outage the grid files are generated and provided but missing data are flagged with the special value of -99.99.
References
- Crowder, R. B., 1995: Wonders of the Weather. Australian Government Publishing Service Canberra.
(General introduction to solar energy budget for the Earth.) - Gautier, C., Diak, G., Masse, S., 1980: A Simple Model to Estimate the Incident Solar Radiation at the Surface from GOES Satellite Data. J. of Appl. Meter. 19 1005-1012.
(Basic method for calculating surface solar radiation from satellite data.) - Weymouth, G., Le Marshall, J., 1994: An Operational System to Estimate Insolation over the Australian Region. Proc. Pacific Ocean Remote Sensing Conference 443-449.
(The description of the model used to calculate the solar radiation over Australia.) - Weymouth, G., Le Marshall, J. F., 2001, Estimation of daily surface solar exposure using GMS-5 stretched-VISSR observations: The system and basic results, Australian Meteorological Magazine, 50, 263-278.
