By Deniz Bozkurt, associate researcher (CR)2, and Roberto Rondanelli, associate researcher (CR)2 and academic DGF-FCFM Universidad de Chile.
Observation of Earth processes is vital to determine the interactions of the elements of the climate system and the role and influence of humans in these interactions. Probably the best example of this is to demonstrate the undeniable role of people in climate change and the planet’s temperature. In remote regions such as the poles, deserts, and oceans, where there are no human settlements and harsh environmental conditions prevail, there are some uncertainties due to insufficient observing networks. However, during the age of satellites, it has become possible to reduce uncertainties by conducting many fundamental analyses, such as greenhouse gases and atmospheric aerosols monitoring, ice sheet change, sea surface temperature, and cloud characteristics for any world region.
A brief history
The first steps in observing the Earth from space were established in the Cold War in the 1950s. Many countries came together to study our planet with the so-called International Year of Geophysics (between 1957 and 1958). ). Following this, the Soviet Union launched the world’s first satellite into space, Sputnik, in October 1957, and later, the United States launched its first satellite into space, Explorer 1, in January 1958.
Indeed, meteorology and atmospheric sciences were important in these efforts and advances. For example, with Explorer 7, launched in 1959, the global heat balance could be monitored and recorded as the world’s first successful remote sensing. The same thing happened with TIROS-1, the first meteorological satellite launched into space in April 1960. Later, in 1963, the World Meteorological Organization established the Global Observing System, which was created with meteorological satellites in fixed and polar orbits.
Today, with dozens of observation satellites operated by space departments and agencies in the United States (NASA), China (CNSA), Russia (ROSCOSMOS), Europe (ESA), and other countries, it is possible to monitor the different components of the climate system, such as the atmosphere and the cryosphere. In addition, a huge source of data is provided through monitoring of climate change and environmental activities, among others.
How do satellites work?
Satellites use radiometers to scan the Earth. They usually have a scanning mechanism consisting of a small telescope or antenna and other devices to detect the electromagnetic radiation emitted from our planet into space in different spectral bands or lines, as if they were robotic eyes looking at the Earth.
Measurements made by these devices are digitized and transmitted to various data centers worldwide and presented as images and data via the Internet or other media. For example, images created with visible radiation (which coincides with what we humans would see from space) can provide useful information for cloud formation, storm forecasting, snow cover, smoke from fires, and dust transport. Infrared images allow the height and temperature of clouds to be determined, either day or night. Important information such as the planet’s radiation budget (the rate of energy entering and leaving the Earth in different parts of the electromagnetic spectrum) can also be determined.
Satellites are placed in one of two types of orbits around the Earth. The first is a fixed orbit (“geostationary orbit”) in which the satellite is at an altitude of about 36,000 kilometers and orbits the equator at the speed of Earth’s rotation. In this way, the satellite can continuously see the same geographic area in high resolution (between 1 and 4 kilometers). These satellites provide most of the images we frequently see on television or the Internet. For example, the GOES-East and GOES-West satellites, controlled by NASA and NOAA, cover many parts of the Western Hemisphere (such as the Western Pacific and the Americas), while the European Space Agency’s Meteosat satellite covers Europe and Africa.
Because these satellites are in a very distant orbit, they require detailed telescopes and precise scanning mechanisms to see the Earth. To overcome these disadvantages, the second type of satellite, polar-orbiting at lower altitudes (approximately 500 to 900 km), has a crucial role to play (Figure 1). These satellites travel in a sun-synchronous orbit, from pole to pole in a circular orbit, making it possible to measure any location on Earth twice a day at the same local time in 24 hours. This measurement range can be extended to a six-hour viewing interval by placing two different satellites in different sun-synchronous orbits. With data provided by these satellites, such as atmospheric temperature, many cloud features, atmospheric humidity, and severe weather events, cryospheric processes can be followed even in the polar regions. Some of them can be a source of essential data for weather forecast models. For example, volcanic eruptions and forest fires can be observed regardless of site conditions.
Examples of the use and importance of satellites
Satellites provide high-quality data useful for atmospheric sciences, oceanography, glaciology, and hydrology. Since satellite images and data can be captured and processed in real-time, one of the most widely used areas is climate analysis and the prediction and monitoring of severe weather events, such as hurricanes, tornadoes, and dense convective clouds. These events can also be predicted and analyzed with satellite data, such as the clouds’ height and temperature, and precipitation intensity. The climatological trend of glacier masses in the polar regions, and their changes during extreme weather events can also be analyzed with satellite views.
Figure 1. NASA-controlled polar-orbiting Earth observation fleet as of 2015. Photo source: NASA (https://climate.nasa.gov/news/2242/briefing-to-highlight-results- from-new-earth-missions/).
Due to this, not having one or two operational satellites (as mentioned in the BBC) could generate a gap in knowledge due to the lack of observations. But, above all, it is worrying that we could lose a massive amount of data on extreme weather events provided by these technological instruments, some of which we will mention in the second part of this article.
NASA Worldview, https://worldview.earthdata.nasa.gov/
NASA Space Laser Missions Map 16 Years of Ice Sheet Loss: https://www.nasa.gov/feature/goddard/2020/nasa-space-laser-missions-map-16-years-of-ice-sheet-loss
The European Space Agency (ESA), https://www.esa.int/