NASA Earth Observation Satellites: Last month on May 25, 2021, NASA announced a new Earth System Observatory which intends to address the mitigation strategies of climate change, natural disasters such as forest fires. This observatory will also be designed to study the scope of real-time improvement in agricultural processes. All the satellites in the observatory will work to complement each other to provide all sorts of information to create a comprehensive and 3D view of Earth. This observatory is right now in the formulation phase. The first planned satellite of this observatory is NISAR (NASA-ISRO Synthetic Aperture Radar) satellite, jointly developed by NASA and ISRO (Indian Space Research Organisation). This article will explore NASA’s Earth Observing System that comprises a series of Earth-orbiting satellites.

Rendering of NISAR satellite, First of the NASA Earth Observation Satellites
Rendering of NISAR satellite, First of the NASA Earth Observation Satellites, Image Credit: NASA

What are Earth Observation Satellites used for?

These are the remote sensing satellites whose basic function is to observe Earth from orbit. Different from intelligence and military satellites, these satellites are used for non-military purposes such as environmental monitoring, weather forecasting, terrain mapping and others. Most of the Earth observation satellites are imaging satellites.

How do Earth Observation Satellites work?

Design and the placement of the satellite decide its functioning. Talking about the orbit, Earth observation satellites are basically placed in two types of orbits, these are geostationary and polar orbit.

Geostationary and Polar-Orbiting Satellites
Geostationary and Polar-Orbiting Satellites, Image Credit: Source

Geostationary Satellites

When viewed from the Earth these type of satellites seems static but actually, these are moving with the rotation of Earth. Their relative velocity with respect to Earth is zero. Geostationary satellites are high altitude satellites and the orbit could be as high as 36000 km from the earth’s surface. However, these satellites provide continuous observation but they fail to observe polar regions due to Earth’s curvature.

Polar orbiting satellites

These are low-altitude satellites and can produce images with a high spatial resolution. polar satellites orbit the Earth around the poles and the rotation period is around 100 minutes. In this manner, 3 of such satellites can observe the entire Earth every 6 hours.

Continuous coverage of geostationary satellites and high-resolution observation of polar satellites can complement each other for a perfect Earth observation.

Read about some first of its kind

Brief History of Earth Observation Satellites

Ever wondered how many Earth observation satellites are there in space? The first artificial remote sensing satellite was launched by the Soviet Union on October 4, 1957. The satellite was named Sputnik 1 and its signals helped in the study of the ionosphere. The first American satellite launched by NASA was Explorer 1 which was launched on January 31, 1958. Data from this satellite helped in discovering Earth’s Van Allen radiation belts. On 17 March 1958 NASA launched Vanguard 1, the oldest satellite still in orbit. It lost its link with the Earth in 1964 but while in function is helped in the first upper atmospheric density measurements. The first satellite specifically designed for Earth observation was Vanguard 2 which launched on 17 February 1959. Due to technical issues, it was not helpful and finally was replaced by TIROS-1, the first successful low-Earth orbital weather satellite. Launched on April 1, 1960. Seeing the success of TIROS satellites, the National Oceanic and Atmospheric Administration (NOAA) series of satellites was also launched.

TIROS 1 the first weather satelliteof NASA
TIROS-1, the first weather satellite of NASA, Image Credit: National Environmental Satellite, Data, and Information Service (NESDIS)

By further extending the coverage of Earth observation NASA launched the Landsat program starting with Landsat-1 on 23 July 1972. It was the 1st satellite launched to study and monitor Earth’s landmasses. With the advancement in RADAR technology, the Earth observation satellites have expanded greatly in numbers. The wealth of iconic images rendered by these satellites has enhanced our understanding of Earth’s terrestrial, aquatic and climatic environment. Satellite-derived maps of the Earth’s climate regions and habitats have been a major advancement in the last few years.

List of NASA’s Earth Observation Satellites

NASA earth observing missions
NASA’s earth observing missions, Image Credit: NASA

Starting from 1958 to 2021 many satellites have been launched by NASA for Earth observation. Some of these satellites have completed their tenure and have stopped working but some are still working. Following is the list of NASA Earth Observation Satellites that are in operation to date.

Satellite NameOrbit TypeMission
Landsat-7Sun-synchronous polarTo monitor Earth’s land and coastal areas by taking repeated images.
Terra (EOS-AM)Circular sun-synchronous polarTo study Earth’s atmosphere, ocean, land, snow & ice, and energy budget to understand the Earth system.
AquaSun synchronous, near polar orbitTo analyze Earth’s water cycle, like evaporation from the oceans, water vapor in the atmosphere, clouds, precipitation, soil moisture, sea ice, land ice, and snow cover on the land and ice.
AuraSun synchronous, near polar orbitTo measure ozone, aerosols and key gases throughout the atmosphere.
CloudSatSun synchronousTo understand Earth’s hydrological cycle and to understand the impact of clouds on Earth’s radiation budget.
CALIPSO Near sun-synchronousTo study the role of clouds and atmospheric aerosols in regulating Earth’s weather, climate, and air quality.
SMAP Sun synchronous, near polar orbitTo monitor soil moisture and provide critical information for drought early warning.
OCO-2 Sun-synchronousFor space-based measurement of primary greenhouse gases on Earth, the Carbon Dioxide or CO2
Landsat-8 Sun synchronous, near polar orbitTo measure Earth’s terrestrial and polar regions in the visible, near-infrared, short wave infrared
ICESat-2Near-circular, near-polar orbitTo analyze ice sheet elevation and sea ice thickness, as well as land topography, vegetation characteristics, and clouds
Download the detaild chart from here.

Conclusion

The biggest contribution of remote sensing satellites is to create a data repository for Earth-system science. There is still a lot of unprocessed data available which might hold some amazing secrets of Earth and its environment. The availability of the imagery data helps promote research to study the environmental changes. real-time imaging is what could be the next step where multinational efforts are also needed for the common good of all.

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