GOES (Geostationary Operational Environmental Satellites) are weather-observing satellites that operate in geosynchronous orbit at an altitude of about 525 miles. Since their launch in 1974, they have been a vital component of the United States’ weather monitoring and forecasting efforts.
Among the many ways in which the Earth’s atmosphere is monitored by GOES are radiometers, instruments that can detect and measure radiation from various atmospheric conditions. These include solar ultraviolet radiation, thermal infrared light from water vapor and cloud tops, and visible light reflected from the surface of the Earth.
Radiation that reaches Earth’s surface is primarily in the form of infrared light. Some of it reflects from the snow, ice, and ground, while some is absorbed by these surfaces. GOES satellites use these reflected light images to help meteorologists identify cloud types, track clouds and provide early warning of severe weather.
Infrared wavelengths can penetrate deep into the atmosphere, where they are emitted by water vapor and clouds. GOES radiometers can detect this radiation and measure its intensity to provide weather data that can be used in a variety of ways.
One of the most common uses for GOES-R imagery is to estimate the thickness of clouds. This can help predict the speed and direction of storms, and to forecast tornadoes, hailstorms, and flash floods.
Another important function of GOES imagery is to monitor the temperature of the air above the Earth’s surface. Temperatures vary widely over the Earth’s surface, and GOES-R has four different bands to measure this information. These include a red band, a blue band, and two bands that are known as “veggie” channels.
GOES imagery is available at a number of resolutions, from a few centimeters to several kilometers. The image quality varies with the type of camera on the satellite, and with the level of detail of the underlying observations.
Some GOES satellites have more than one radiometer, so their resulting images are more accurate and useful. For example, a satellite with a 5-channel Advanced Very High Resolution Radiometer (AVHRR) can capture more infrared wavelengths than a satellite with a 4-channel radiometer.
There are also a few GOES satellites that are equipped with additional sensors, including the Geostationary Lightning Mapper (GLM). GLM is able to measure when lightning strikes the ground or when lightning develops in the clouds, and it can help forecast storm severity and tornadoes.
Visible light imagery is available only during daylight hours and is an essential part of a GOES satellite’s weather-monitoring mission. This is because sunlight reflected off the tops of clouds and from the Earth’s surface is the same radiation needed to take regular photographs.
It is also important to note that GOES is an instrument-dependent system, meaning that the performance of each GOES satellite is dependent on the performance of the sensors that are installed on it. The GOES-R satellite, for instance, carries the Advanced Baseline Imager (ABI) to enable multispectral imaging.
GOES satellites are the world’s most successful and widely used Earth-monitoring weather-observing systems, with over 100 operational satellites in orbit at any given time. Their continuous weather imagery and their ability to keep a watch on the weather over the North American continent have helped GOES become a vital and effective tool for monitoring the environment and helping to improve weather forecasting.