Weather satellites collect data on a variety of meteorological parameters, such as rain, snow, ice, fire, cloud systems, dust storms, air pollution, ocean currents and more. The data is used by meteorologists and climatologists to monitor current conditions and predict future weather events.
There are two main types of weather satellites: polar orbiting and geostationary. Each type meets the needs of forecasters and emergency responders differently.
1. Polar Orbiting Satellites
Before the dawn of the satellite era, weather forecasters had to draw their maps by hand, and computer models were almost unheard of. But that all changed in 1960 when the first weather satellite, Tiros-I, was launched from the Earth. Today, a fleet of polar and geostationary weather satellites provide weather forecasters with detailed observations that enable them to make more accurate forecasts.
The number of meteorological satellites in orbit is estimated to be more than 8,261 as of January 2022, according to the United Nations Office for Outer Space Affairs (UNOOSA). The top 10 countries in terms of operational satellites are the United States, Russia, China, Japan, India, France, Canada, Germany and Luxembourg.
Polar Orbiting Satellites
The simplest type of weather satellite is a polar orbiting satellite. These satellites circle the Earth twice a day, collecting data as they move from pole to pole. These satellites are typically used for weather reconnaissance or observation.
These satellites are typically at a relatively low altitude, about 850 kilometers (500 miles) above the Earth’s surface. These satellites are able to collect high-resolution images of large areas, which are useful for atmospheric studies, including cloud formation and storm systems.
They can also be used to map the Earth. Many communication satellites, such as the Iridium constellation, use a polar orbit to provide telecommunication services.
There are three primary types of polar orbiting satellites: the Lagrangian point orbit, the synchronous orbit and the circular polar orbit. The synchronous orbit is the most common orbit for communication satellites. It is a Sun-synchronous orbit, so that it passes over any given point at the same local mean solar time.
It is also possible to place a satellite in a nearly-polar orbit, but it does not cross the Earth’s poles directly. This type of orbit is called a ‘Lagrangian point’ orbit, and it can help us monitor the solar wind before it reaches Earth.
The ‘Lagrangian point’ orbit is particularly useful in the study of climate change. It allows us to measure the ‘cloud fractional cover’ of the atmosphere, which is important in estimating the amount of water vapor in the air.
However, there are some disadvantages to these orbits. One is that they don’t have a fixed view of the Earth since it rotates beneath their path, so they don’t have a continuous coverage of the Earth as a whole like geostationary satellites do. Another is that they don’t have a long-range communications capability, meaning that they won’t be able to communicate continuously with a single location on the Earth’s surface.
The National Oceanic and Atmospheric Administration (NOAA) operates a large fleet of polar orbiting satellites to support its meteorological services. They are designated as “POES” (Polar Orbiting Environmental Satellite) satellites and are classified by number. NOAA has an online POES Spacecraft Status webpage to keep track of the status of each polar orbiter.
2. Geostationary Satellites
Geostationary satellites (GEO) orbit the Earth at a fixed distance of 35,786 km, which matches the speed of the Earth’s rotation. This enables them to remain in the same position over a single longitude on the surface of the Earth, even though they may drift north to south over time. These satellites are often used for telecommunications, and they have many advantages over polar orbiting satellites.
In fact, the majority of communication satellites are in GEO. These are commonly used for voice, data, and video services and support a variety of businesses across the globe.
These satellites are also useful for Earth observation, as they can continuously “see” large areas of the planet. This makes them an ideal choice for weather monitoring, as they can detect and track changes in the Earth’s surface over time.
A number of countries have operational geostationary meteorological satellite systems, such as the United States’ GOES (Geostationary Operational Environmental Satellites) and EUMETSAT’s Meteosat satellite systems. They carry a variety of instruments for weather forecasting, atmospheric research, and global climate studies.
The GOES satellites are particularly useful for short-range weather forecasting, and they often monitor areas of severe weather as frequently as every 30 seconds. They are also used for search and rescue.
However, these satellites have a few limitations. For one thing, they are not able to provide full geographical coverage, as they cannot reach the high latitudes where many ground stations are located.
This is a problem for some communication systems, since they need to be able to point their antennas at a high enough altitude that the signals can be received reliably. This is why some telecommunications companies use different types of satellites to get their signal to the ground.
Another limitation of these satellites is that they can drift out of their equatorial orbit over time, due to the effects of the sun and the moon on their orbital motions. These drifts are typically countered by a process known as station keeping, which involves periodically correcting the slowly increasing inclination back to zero in the northern and east-western hemispheres.
These satellites have also been equipped with attitude control devices, such as momentum wheel gyros or thrusters. These are adapted to the specific tasks of the satellite and are controlled by a computer.
The International Telecommunication Union (ITU) assigns so-called “parking spots” for these satellites, in order to prevent them from interfering with each other and with the operation of telecommunications systems. The ITU also sets the limits on the frequency interference that can arise between these satellites.
3. Earth Observing Satellites
There are currently more than 5,465 operational satellites in orbit around the Earth. Many of these are Earth observation (EO) satellites, which use sensors to collect information about the Earth’s natural and manmade environments.
These satellites provide vital data on things such as the health of our planet, its climate and weather. They help us to understand our environment, make better decisions and improve the lives of those who live on or near it.
They also allow us to track and monitor natural hazards, such as earthquakes, volcanoes and tsunamis. They can even help keep us safe on land, like by enabling the detection of mines.
The number of weather satellites in orbit is growing, with more being launched every year. In fact, there are now a total of 16 weather-observing satellites in space. The oldest, the Tropical Rainfall Measuring Mission (TRMM), was launched in 1997 and the youngest, Landsat 8, is slated for launch in 2013.
It’s important to remember that all of these satellites have their own missions, meaning they are built to perform specific tasks. For example, a GPS satellite might be designed to measure your location, but its payload is designed to give you directions.
Aside from collecting weather data, Earth observation satellites are also used to study our oceans. Their payloads include sensors that measure the amount of sunlight on the ocean surface, which is a key indicator of water quality.
Similarly, the amount of solar radiation hitting the atmosphere is a major factor in determining air pollution levels. In this way, satellites can contribute to the fight against airborne diseases such as smog and ozone depletion.
In addition to the information gathered from these satellites, they are also used to create maps and imagery of the Earth. These images can then be used to support a wide range of research and development activities.
For example, the United States Environmental Protection Agency has used satellites to track ozone depletion and its impact on global climate. Its Nimbus 7 total ozone mapping spectrometer has helped to develop an unprecedented map of the Arctic and Antarctic ozone “holes.”
Other NASA projects have used EO to monitor ice on the seafloor, to detect and document the effects of human activities on marine resources and to provide new knowledge about the health of the ocean. It is these observations that have allowed researchers to develop a greater understanding of the impact of climate change on our oceans, and to monitor the effectiveness of policy interventions.
Today, more than half of the world’s active satellites are launched for commercial purposes. About 61% of these have communication and navigation functions, while 27% are Earth observation satellites.