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.
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 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.
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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.
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
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 Name | Orbit Type | Mission |
|---|---|---|
| Landsat-7 | Sun-synchronous polar | To monitor Earth’s land and coastal areas by taking repeated images. |
| Terra (EOS-AM) | Circular sun-synchronous polar | To study Earth’s atmosphere, ocean, land, snow & ice, and energy budget to understand the Earth system. |
| Aqua | Sun synchronous, near polar orbit | To 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. |
| Aura | Sun synchronous, near polar orbit | To measure ozone, aerosols and key gases throughout the atmosphere. |
| CloudSat | Sun synchronous | To understand Earth’s hydrological cycle and to understand the impact of clouds on Earth’s radiation budget. |
| CALIPSO | Near sun-synchronous | To study the role of clouds and atmospheric aerosols in regulating Earth’s weather, climate, and air quality. |
| SMAP | Sun synchronous, near polar orbit | To monitor soil moisture and provide critical information for drought early warning. |
| OCO-2 | Sun-synchronous | For space-based measurement of primary greenhouse gases on Earth, the Carbon Dioxide or CO2 |
| Landsat-8 | Sun synchronous, near polar orbit | To measure Earth’s terrestrial and polar regions in the visible, near-infrared, short wave infrared |
| ICESat-2 | Near-circular, near-polar orbit | To analyze ice sheet elevation and sea ice thickness, as well as land topography, vegetation characteristics, and clouds |
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.