SARAL
Encyclopedia
SARAL or Satellite with ARgos and ALtiKa is a cooperative altimetry technology mission of Indian Space Research Organisation
(ISRO) and CNES
(Space Agency of France). The ISRO built satellite with payloads modules (AltiKa altimeter, DORIS
, Laser Retroreflector Array (LRA) and ARGOS-3 (Advanced Research and Global Observation Satellite) data collection system provided CNES will be launched by Indian Polar Satellite Launch Vehicle
rocket into the Sun-synchronous orbit
(SSO). ISRO will be responsible for the platform, launch, and operations of the spacecraft. A CNES/ISRO MOU (Memorandum of Understanding) on the SARAL mission was signed on Feb. 23, 2007.
The SARAL satellite, carrying AltiKa and an Argos-3 instrument2, is scheduled to be launched in early 2011.
/NOAA and CNES/EUMETSAT. It will fill the gap between Envisat
and the Sentinel 3
mission of the European GMES program. The combination of two altimetry missions in orbit has a considerable impact on the reconstruction of sea surface height
(SSH), reducing the mean mapping error by a factor of 4.
AltiKa, the altimeter and prime payload of the SARAL mission, will be the first spaceborne altimeter to operate at Ka band
. AltiKa is set to take over ocean-monitoring from Envisat. It is the first to operate at such a high frequency, making it more compact and delivering better performance than the previous generation.
While existing satellite-borne altimeters determine sea level by bouncing a radar signal off the surface and measuring the return-trip time, AltiKa operates at a high frequency in Ka band. The advantage of this is twofold. One, the earth’s atmosphere slows down the radar signal, so altimetry measurements are skewed and have to carry additional equipment to correct for this error. Since AltiKa uses a different system, it does not have to carry an instrument to correct for atmospheric effects as current-generation altimeters do.
AltiKa gets round this problem by operating at a high frequency in Ka band, which also means it doesn’t have to carry an instrument to correct for atmospheric effects as current-generation altimeters do
The second advantage of operating at higher frequencies is greater accuracy. AltiKa will measure ocean surface topography
with an accuracy of 8 mm, against 2.5 cm on average using current-generation altimeters, and with a spatial resolution of 2 km.
The disadvantage, however, is that high-frequency waves are extremely sensitive to rain, even drizzle. 10% of the data is expected to be lost.
Indian Space Research Organisation
The Indian Space Research Organisation is an independent Indian governmental agency established in 1969 for the research and development of vehicles and activities for the exploration of space within and outside of Earth’s atmosphere. Headquartered in Bangalore...
(ISRO) and CNES
CNES
The is the French government space agency . Established under President Charles de Gaulle in 1961, its headquarters are located in central Paris and it is under the supervision of the French Ministries of Defence and Research...
(Space Agency of France). The ISRO built satellite with payloads modules (AltiKa altimeter, DORIS
DORIS (geodesy)
Doppler Orbitography and Radiopositioning Integrated by Satellite is a French satellite system used for the determination of satellite orbits and for positioning.-Principle:...
, Laser Retroreflector Array (LRA) and ARGOS-3 (Advanced Research and Global Observation Satellite) data collection system provided CNES will be launched by Indian Polar Satellite Launch Vehicle
Polar Satellite Launch Vehicle
The Polar Satellite Launch Vehicle , commonly known by its abbreviation PSLV, is an expendable launch system developed and operated by the Indian Space Research Organisation . It was developed to allow India to launch its Indian Remote Sensing satellites into sun synchronous orbits, a service that...
rocket into the Sun-synchronous orbit
Sun-synchronous orbit
A Sun-synchronous orbit is a geocentric orbit which combines altitude and inclination in such a way that an object on that orbit ascends or descends over any given point of the Earth's surface at the same local mean solar time. The surface illumination angle will be nearly the same every time...
(SSO). ISRO will be responsible for the platform, launch, and operations of the spacecraft. A CNES/ISRO MOU (Memorandum of Understanding) on the SARAL mission was signed on Feb. 23, 2007.
The SARAL satellite, carrying AltiKa and an Argos-3 instrument2, is scheduled to be launched in early 2011.
Mission
The SARAL mission is complementary to the Jason-2 mission of NASANASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
/NOAA and CNES/EUMETSAT. It will fill the gap between Envisat
Envisat
Envisat is an Earth-observing satellite. It was launched on 1 March 2002 aboard an Ariane 5 from the Guyana Space Centre in Kourou, French Guyana into a Sun synchronous polar orbit at an altitude of...
and the Sentinel 3
Sentinel 3
Sentinel 3 is a future space mission from ESA, the third in the GMES program.It will provide medium resolution optical and radar altimetry Earth observation data...
mission of the European GMES program. The combination of two altimetry missions in orbit has a considerable impact on the reconstruction of sea surface height
Sea surface height
Sea surface height is the height of the ocean's surface. On a daily basis, SSH is most obviously affected by the tidal forces of the Moon and the Sun acting on the Earth. Over longer timescales, SSH is influenced by ocean circulation. Typically, SSH anomalies resulting from these forces differ...
(SSH), reducing the mean mapping error by a factor of 4.
AltiKa, the altimeter and prime payload of the SARAL mission, will be the first spaceborne altimeter to operate at Ka band
Ka band
The Ka band covers the frequencies of 26.5–40 GHz. The Ka band is part of the K band of the microwave band of the electromagnetic spectrum. This symbol refers to "K-above" — in other words, the band directly above the K-band...
. AltiKa is set to take over ocean-monitoring from Envisat. It is the first to operate at such a high frequency, making it more compact and delivering better performance than the previous generation.
While existing satellite-borne altimeters determine sea level by bouncing a radar signal off the surface and measuring the return-trip time, AltiKa operates at a high frequency in Ka band. The advantage of this is twofold. One, the earth’s atmosphere slows down the radar signal, so altimetry measurements are skewed and have to carry additional equipment to correct for this error. Since AltiKa uses a different system, it does not have to carry an instrument to correct for atmospheric effects as current-generation altimeters do.
AltiKa gets round this problem by operating at a high frequency in Ka band, which also means it doesn’t have to carry an instrument to correct for atmospheric effects as current-generation altimeters do
The second advantage of operating at higher frequencies is greater accuracy. AltiKa will measure ocean surface topography
Ocean surface topography
The ocean surface has highs and lows, similar to the hills and valleys of Earth's land surface depicted on a topographic map. These variations, called "ocean surface topography" or "dynamic sea surface topography" are mapped using measurements of sea surface height relative to Earth's geoid...
with an accuracy of 8 mm, against 2.5 cm on average using current-generation altimeters, and with a spatial resolution of 2 km.
The disadvantage, however, is that high-frequency waves are extremely sensitive to rain, even drizzle. 10% of the data is expected to be lost.