Before the satellites
Until the late 1950s, forecasters worked mainly from ground stations, balloons, ships, aircraft and radar. These gave detailed readings at particular points, but large parts of the world, especially the oceans, had very few observations. A storm could develop in an area where nobody was measuring it. The idea of looking at weather from above had been discussed for years, and the arrival of rockets made it a practical question.
TIROS-1
The first satellite generally recognized as a weather satellite is TIROS-1, launched on April 1, 1960. The name stands for Television Infrared Observation Satellite. It was built by RCA for the U.S. government, with the Army and the newly formed NASA involved in the project, and it was launched from Cape Canaveral. It was small, a drum-shaped satellite about 107 centimeters (42 inches) across, covered with solar cells and carrying two television cameras. Its orbit was roughly circular and a few hundred miles above Earth, so each camera saw only a limited area at any time.
The pictures were crude by modern standards: black-and-white images, taken on command or stored on tape and played back when the satellite passed over a ground station. They were nevertheless the first widely seen views of cloud patterns from space. Forecasters could see for the first time the large spirals of storms and the long bands of clouds along fronts, features that previously had been pieced together from scattered reports. The satellite operated for about 78 days.
Earlier satellites carried some weather-related instruments. Vanguard 2 in 1959 was designed to measure cloud cover but returned data that was hard to use because of the way the satellite spun. Explorer 7, also in 1959, carried instruments measuring the balance of incoming and outgoing radiation. These are sometimes mentioned as predecessors, but TIROS-1 is the one usually credited as the first successful weather observation satellite.
What the pictures changed
The first images did not instantly change daily forecasts. The satellite’s cameras and orbit meant that coverage was patchy, and it took time to develop methods for interpreting the images. Even so, the effect on understanding was large. Meteorologists could see how clouds were organized across thousands of miles, which supported research on how storms form and move.
Over the next few years, the program continued with additional TIROS satellites and then operational versions. Cloud pictures began to be used in routine analysis, and tropical storms and hurricanes could be spotted over oceans where they had once gone unnoticed. In many countries, a satellite view eventually became a normal part of weather maps and broadcasts. A forecast based on data from satellites is, however, still built on the older measurements discussed in our article on forecasting instruments.
Polar and geostationary orbits
Two main orbit types developed.
- Polar orbiting satellites: these circle the Earth from pole to pole at a few hundred miles’ altitude, scanning the planet in strips as it rotates below. They provide detailed views of all regions, including the poles, but only a few passes per location each day. The Nimbus series, starting in 1964, was an important research line, and operational polar-orbiting satellites followed.
- Geostationary satellites: placed at about 35,786 kilometers above the equator, they move in step with the Earth and therefore watch the same area constantly. ATS-1, launched in 1966, provided early pictures from this orbit, and the SMS and GOES series, starting in the mid-1970s, brought routine geostationary coverage to the United States. Europe’s Meteosat and Japan’s satellites followed. The idea of a satellite fixed over one spot goes back to the communications ideas covered in our article on communications satellites.
The two approaches complement each other: polar orbiters give high-resolution detail, while geostationary satellites give continuous monitoring of developing systems.
Instruments beyond cameras
Later satellites carried more than television cameras. Infrared sensors made it possible to see clouds at night and to estimate cloud-top temperatures, which helps indicate how high they are. Other instruments measured the temperature and moisture of the atmosphere at different heights, sea-surface temperature, ice and snow cover, and winds estimated by following cloud movement in successive images. Many of these techniques are the basis of today’s computer weather models, which assimilate large quantities of satellite data.
Limits and perspective
Satellites did not replace other tools. Radar remains the main tool for rain and severe storms near the ground, as discussed in our article on weather radar, and ground observations are still essential. Satellite images are also not forecasts, only observations that need interpretation. Even today, forecasts remain uncertain, particularly beyond a week or so, and satellites have not changed that basic fact.
Still, TIROS-1 marked a turning point. It showed that the Earth’s atmosphere could be watched as a whole, and the improvements that followed in the 1960s and 1970s extended that idea into regular practice. The later move toward near real-time monitoring is the subject of our article on short-term forecasting.