Earth observation satellite
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An Earth observation satellite or Earth remote sensing satellite is a satellite used or designed for Earth observation (EO) from orbit, including spy satellites and similar ones intended for non-military uses such as environmental monitoring, meteorology, cartography and others. The most common type are Earth imaging satellites, that take satellite images, analogous to aerial photographs; some EO satellites may perform remote sensing without forming pictures, such as in GNSS radio occultation.
The first occurrence of satellite remote sensing can be dated to the launch of the first artificial satellite, Sputnik 1, by the Soviet Union on October 4, 1957.[1] Sputnik 1 sent back radio signals, which scientists used to study the ionosphere.[2] NASA launched the first American satellite, Explorer 1, on January 31, 1958. The information sent back from its radiation detector led to the discovery of the Earth's Van Allen radiation belts.[3] The TIROS-1 spacecraft, launched on April 1, 1960 as part of NASA's Television Infrared Observation Satellite (TIROS) program, sent back the first television footage of weather patterns to be taken from space.[1]
As of 2008[update], more than 150 Earth observation satellites were in orbit, recording data with both passive and active sensors and acquiring more than 10 terabits of data daily.[1]
Most Earth observation satellites carry instruments that should be operated at a relatively low altitude. Most orbit at altitudes above 500 to 600 kilometers (310 to 370 mi). Lower orbits have significant air-drag, which makes frequent orbit reboost maneuvers necessary. The Earth observation satellites ERS-1, ERS-2 and Envisat of European Space Agency as well as the MetOp spacecraft of EUMETSAT are all operated at altitudes of about 800 km (500 mi). The Proba-1, Proba-2 and SMOS spacecraft of European Space Agency are observing the Earth from an altitude of about 700 km (430 mi). The Earth observation satellites of UAE, DubaiSat-1 & DubaiSat-2 are also placed in Low Earth Orbits (LEO) orbits and providing satellite imagery of various parts of the Earth.[4][5]
To get (nearly) global coverage with a low orbit, a polar orbit is used. A low orbit will have an orbital period of roughly 100 minutes and the Earth will rotate around its polar axis about 25° between successive orbits. The ground track moves towards the west 25° each orbit, allowing a different section of the globe to be scanned with each orbit. Most are in Sun-synchronous orbits.
A geostationary orbit, at 36,000 km (22,000 mi), allows a satellite to hover over a constant spot on the earth since the orbital period at this altitude is 24 hours. This allows uninterrupted coverage of more than 1/3 of the Earth per satellite, so three satellites, spaced 120° apart, can cover the whole Earth except the extreme polar regions. This type of orbit is mainly used for meteorological satellites.
History
Herman Potočnik explored the idea of using orbiting spacecraft for detailed peaceful and military observation of the ground in his 1928 book, The Problem of Space Travel. He described how the special conditions of space could be useful for scientific experiments. The book described geostationary satellites (first put forward by Konstantin Tsiolkovsky) and discussed communication between them and the ground using radio, but fell short of the idea of using satellites for mass broadcasting and as telecommunications relays.[6]
Applications
Weather
A weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth.[7] These meteorological satellites, however, see more than clouds and cloud systems. City lights, fires, effects of pollution, auroras, sand and dust storms, snow cover, ice mapping, boundaries of ocean currents, energy flows, etc., are other types of environmental information collected using weather satellites.
Weather satellite images helped in monitoring the volcanic ash cloud from Mount St. Helens and activity from other volcanoes such as Mount Etna.[8] Smoke from fires in the western United States such as Colorado and Utah have also been monitored.
Environmental monitoring
Other environmental satellites can assist environmental monitoring by detecting changes in the Earth's vegetation, atmospheric trace gas content, sea state, ocean color, and ice fields. By monitoring vegetation changes over time, droughts can be monitored by comparing the current vegetation state to its long term average.[9] For example, the 2002 oil spill off the northwest coast of Spain was watched carefully by the European ENVISAT, which, though not a weather satellite, flies an instrument (ASAR) which can see changes in the sea surface. Anthropogenic emissions can be monitored by evaluating data of tropospheric NO2 and SO2.
These types of satellites are almost always in Sun-synchronous and "frozen" orbits. A sun-synchronous orbit passes over each spot on the ground at the same time of day, so that observations from each pass can be more easily compared, since the sun is in the same spot in each observation. A "frozen" orbit is the closest possible orbit to a circular orbit that is undisturbed by the oblateness of the Earth, gravitational attraction from the sun and moon, solar radiation pressure, and air drag.
Mapping
Terrain can be mapped from space with the use of satellites, such as Radarsat-1[10] and TerraSAR-X.
See also
- Committee on Earth Observation Satellites
- Data collection satellite
- Earth observation
- Earth observation satellites transmission frequencies
- Earth Observing System - a NASA program comprising a series of satellite missions
- First images of Earth from space
- Imaging satellites
- List of Earth observation satellites
- Space telescope
- Satellite imagery
References
- ^ a b c Tatem, Andrew J.; Goetz, Scott J.; Hay, Simon I. (2008). "Fifty Years of Earth-observation Satellites". American Scientist. 96 (5): 390–398. doi:10.1511/2008.74.390. PMC 2690060. PMID 19498953.
- ^ Kuznetsov, V.D.; Sinelnikov, V.M.; Alpert, S.N. (June 2015). "Yakov Alpert: Sputnik-1 and the first satellite ionospheric experiment". Advances in Space Research. 55 (12): 2833–2839. Bibcode:2015AdSpR..55.2833K. doi:10.1016/j.asr.2015.02.033.
- ^ "James A. Van Allen". nmspacemuseum.org. New Mexico Museum of Space History. Retrieved 14 May 2018.
- ^ "DubaiSat-2, Earth Observation Satellite of UAE". Mohammed Bin Rashid Space Centre.
- ^ "DubaiSat-1, Earth Observation Satellite of UAE". Mohammed Bin Rashid Space Centre.
- ^ "Introduction to satellite". www.sasmac.cn. 2 September 2016.
- ^ NESDIS, Satellites. Retrieved on 4 July 2008
This article incorporates text from this source, which is in the public domain.
- ^ NOAA, NOAA Satellites, Scientists Monitor Mt. St. Helens for Possible Eruption. Retrieved on 4 July 2008 This article incorporates text from this source, which is in the public domain.
- ^ NASA, Drought. Archived 19 August 2008 at the Wayback Machine Retrieved on 4 July 2008 This article incorporates text from this source, which is in the public domain.
- ^ Grunsky, E.C. The use of multi-beam Radarsat-1 satellite imagery for terrain mapping. Retrieved on 4 July 2008
External links
- EO Portal directory
- The TIROS I and II Ground Control Station where the first Earth Observing Satellite (TIROS I) sent it first photos
Template:Space-based meteorological observation
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