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MAKING THE MODERN WORLD
Stories about the lives we've made

module:Weather forecasting

Technology and chaos

page:Satellite monitoring from space


Earth, as seen from a weather satellite, late 20th century. The ability to view weather systems of the entire globe at a moment in time has contributed enormously to our ability to forecast. picture zoom © Science Museum/Science and Society Picture Library

By viewing weather systems over whole regions of the planet – especially regions such as oceans where data was previously very sparse – satellites give forecasters new advantages and new insights into weather and climate. Tiros - the first weather satellite - was launched by the USA on 1 April 1960, just over three years after the Russians launched Sputnik in October 1957.


Artist’s impression of the TIROS 1. Originally, satellites were limited in the information they could return to earth - TIROS only measured visible light and data transmission was very slow. picture zoom © National Aeronautics & Space Administration

The design of weather satellites has to take into account two key things; what kind of imagery is required and which part of the world it is required for. In terms of image type, satellite sensors can take images in different parts of the electromagnetic spectrum. The most useful parts of the spectrum for weather forecasting are visible light and infrared.

Comparing weather images

Visible light sensors

Visible light sensors provide detailed visual data on cloud shapes, textures, patterns and thicknesses, clearly discriminating between cloud and land or sea. Unfortunately, these sensors only provide data during daylight hours and the appearance of features varies with the angle of the Sun.

Infrared sensors: Temperature

The infrared spectrum is very sensitive to temperature and channels are visible both day and night. Different tones on infrared temperature sensor images indicate detailed temperature data of land, sea or cloud surfaces. Combined with other data, cloud height, thickness and likely nature of precipitation can be estimated. Unfortunately, the physical structure of weather systems can be difficult to make out on infrared sensor images, since air temperature rather than cloud is being observed. Features such as low stratus and fog can be difficult to see.

Infrared sensors: Water vapour

Certain ranges of the infrared spectrum are strongly absorbed by water vapour; images in this part of the spectrum therefore show the presence or absence of water vapour in the atmosphere. Water vapour infrared sensors provide data on water vapour content of the air even if no clouds are visible. This allows forecasters to see circulation patterns which might influence future weather conditions. As with infrared temperature sensors, the physical structure of weather systems can be difficult to make out, though in this case moisture rather than cloud is being observed.

By combining different sensors on the same satellite a range of different images – each providing slightly different information – can be obtained.

ACTIVITY

 

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Modern satellites can transmit up to 40 images an hour and images can be observed in up to 5 different regions of the spectrum, giving an enormously powerful and flexible way of studying the atmosphere, oceans and land. picture zoom © National Aeronautics & Space Administration

The images in the activity are all from Meteosat, a geostationary satellite. There are two fundamentally different approaches to placing weather satellites in orbit depending on the field of view, location monitored and amount of detail required.

Polar orbiter: 670 km above surface


Polar orbiter

Successive swathes of Earth are viewed as the Earth turns beneath the polar orbiter satellite. High-resolution images are obtained but with a more limited field of view. To view the same place again you have to wait for a further satellite orbit to be completed.

Geostationary: 36,000 km above surface


Geostationary satellite

Geostationary satellites move round Earth at same speed as the Earth turns so it is always overhead with same area in view. This allows for a larger viewing area but the images are in less detail due to the greater distance.


TIROS V, launched June 19, 1962, captures an image of Typhoon Ruth showing distinct eye. The advent of satellite technology transformed the way forecasters could view weather systems and predict their movement. picture zoom © Science Museum/Science and Society Picture Library


Resource Descriptions

Earth, as seen from a weather satellite, late 20th century. The ability to view weather systems of the entire globe at a moment in time has contributed enormously to our ability to forecast.
Artist’s impression of the TIROS 1. Originally, satellites were limited in the information they could return to earth - TIROS only measured visible light and data transmission was very slow.
Modern satellites can transmit up to 40 images an hour and images can be observed in up to 5 different regions of the spectrum, giving an enormously powerful and flexible way of studying the atmosphere, oceans and land.
TIROS V, launched June 19, 1962, captures an image of Typhoon Ruth showing distinct eye. The advent of satellite technology transformed the way forecasters could view weather systems and predict their movement.
Scene  Rich Media