Jul 20, 2023
As you get ready to leave your house, you might ask yourself a few questions to make sure you are ready for the day: Do I have my keys and wallet? Is there a test in science class today, or is that tomorrow? Did I pack all the materials I need for that important meeting at work today?
And perhaps one of the most universal questions is: What will the weather be like?
In modern society, we often take the daily weather report for granted. We turn on the news, open the weather app on our smart phone, or look up our region’s weather on the internet. Have you ever thought about how meteorologists predict the forecast? For a big part of the answer, we need to look to the sky.
The world’s first weather satellite, TIROS-1 (Television InfraRed Observation Satellite), was launched on April 1, 1960. It provided more than 22,000 pictures of the Earth from orbit. This new way to look at Earth's weather revolutionized the science of storm prediction. Now even the most remote places on Earth could be monitored regularly. Between 1960 and 1965, nine more satellites were launched in the TIROS program. TIROS instruments included wide- and narrow-angle television cameras.
The TOS (TIROS Operational System) satellites represented a step up from the initial TIROS satellites, moving from a research and development phase into a fully operational system. ITOS (Improved TIROS Operational System) satellites were the second generation of TIROS operational satellites. ITOS-1, launched in January 1970, greatly surpassed the performance of the earlier satellites by providing both direct transmission and storage of television and infrared imagery. Later ITOS spacecraft also supplied vertical profiles of atmospheric temperature. ITOS satellites remained in service through 1979.
TIROS-N was the first in the series of third-generation polar orbiting operational satellites. Launched in 1978, TIROS-N was equipped with instruments for visible and infrared imaging, ocean temperature readings, and atmospheric studies.
Launched in 2002, NOAA 17 was at the time the most advanced TIROS-N (ATN) series of satellites. Like its predecessors, this polar-orbiting spacecraft supports environmental monitoring instruments for the imaging and measurement of the Earth’s atmosphere, surface, and cloud cover. The last satellite in this series was NOAA-19, launched 6 February 2009.
The main instrument of the NOAA satellites, the AVHRR (Advanced Very High Resolution Radiometer) collects a variety of data, including the properties of vegetation, cloud cover, snow, ice cover, and land and sea surface. NOAA 17 was also the third spacecraft in the series to carry microwave instruments for the collection of temperature, moisture, surface, and hydrological data in cloudy regions where visible and infrared instruments are not as effective.
Another type of satellite, GOES (Geostationary Operational Environmental Satellite) is designed to constantly monitor the same region of the Earth. They are placed in geostationary orbit at 35,800 kilometers (about 22,000 miles) above the equator. At this altitude, a satellite orbits once per day, so it remains fixed over one spot on the ground. From this vantage point, GOES can provide continuous coverage of a region’s daily weather developments as well as warnings of severe storms to come.
Since the first launch in 1975, GOES spacecraft have gone through several generations of technical development. Unlike previous spin-stabilized satellites, the current GOES series has a three-axis body-stabilized design that allows its sensors to continuously point towards the Earth. A rotating solar array supplies power, and a long solar sail boom balances the craft.
What are all these satellites looking at? What can they tell us about the weather? There are three main types of satellite imagery used today: visible imagery, infrared imagery, and water vapor imagery. Visible satellite imagery can only be viewed during the day, when clouds are reflecting the light from the Sun. With these images, clouds show up white, with the ground and ocean grey and dark. Visible images are useful for monitoring developing thunderstorms. Infrared imagery uses sensors that measure heat radiating off things like clouds or the surface of the Earth. Because it does not rely on light the same way visible imagery does, they can be viewed during the day and night. Infrared imagery is useful in measuring the intensity of storms and identifying other meteorological features like fog. Water vapor imagery indicates how much moisture is present in the upper atmosphere. These images are useful for identifying when heavy rain is possible.
Clouds are the most obvious features appearing on satellite weather imagery. Close-up views reveal complex and delicate patterns, from crisscrossing streaks and oceanlike waves, to massive storm systems and swirling eddies in the wakes of islands. To meteorologists these cloud images supply useful and interesting data. Looking at clouds in infrared wavelengths gives their temperature.
Satellites also play a vital role in tracking the path of storms and monitoring their strength. From up above, storms such as hurricanes become big swirling masses of cloud and wind that work their way across the globe. Being able to track big storms allows meteorologists to warn affected areas to board up their property and hunker down or even evacuate until the storm passes.
Satellite imagery can also provide us with information about the environment beyond the daily forecast. For example, data gathered by satellites can be used to produce images of ash plumes from active volcanoes. Beyond its geological and meteorological applications, this imagery also helps aircraft avoid dangerous concentrations of ash.
Air pollution, haze, and dust can be detected on weather satellite imagery.
Meteorological satellites look at Earth to study the weather and atmosphere. Satellite weather images provide a wealth of information quickly and continuously. This information, especially as it is used in storm predictions, has often proved vital to the preservation of lives and property. Moreover, this technology has become an integral part of our everyday lives. So next time you walk out for front door, umbrella in tow for that upcoming afternoon shower, thank your nearest meteorological satellite!
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