SARAL

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). SARAL performs altimetric measurements designed to study ocean circulation and sea surface elevation.[2][6]

SARAL
An artist's rendering of Satellite with ARgos and ALtika - SARAL
Mission typeRemote sensing
OperatorISRO
CNES
COSPAR ID2013-009A
SATCAT no.39086
Websitehttps://www.ursc.gov.in/earth-observation/html/saral-1.jsp
Mission duration5 years (ARGOS)
3 years (AltiKa)
Spacecraft properties
BusIMS-2
ManufacturerISRO Satellite Centre
CNES
Launch mass407 kilograms (897 lb)[1][2]
Start of mission
Launch date25 February 2013, 12:31 (2013-02-25UTC12:31Z) UTC[3]
RocketPSLV-CA
Launch siteSatish Dhawan FLP
Orbital parameters
Reference systemGeocentric
RegimeSun-synchronous
Perigee altitude790 kilometres (490 mi)
Apogee altitude791 kilometres (492 mi)
Inclination98.54 degrees
Period100.54 minutes
Epoch30 October 2013, 02:13:46 UTC[4]
Main radar
WavelengthsKa band[5]
Instruments
ALTIKA, DORIS, LRA, ARGOS-3
 

The payload modules were provided by CNES: ALTIKA (altimeter), DORIS, Laser Retro-reflector Array (LRA), and ARGOS-3 (Advanced Research and Global Observation Satellite) data collection system. ISRO is responsible for the platform (Indian Mini Satellite-2 bus), launch (Polar Satellite Launch Vehicle rocket), and operations of the spacecraft. SARAL was successfully launched into a Sun-synchronous orbit (SSO) on 25 February 2013, 12:31 UTC.[7][8]

Mission

The SARAL mission is complementary to the Jason-2 mission of NASA/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.[9]

Payloads

Ka band Altimeter (ALTIKA)

ALTIKA, the altimeter and prime payload of the SARAL mission, is the first spaceborne altimeter to operate at Ka band.[10] It was built by the French National Space Agency CNES. The payload is intended for oceanographic applications, operates at 35.75 GHz.[1] 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.[11]

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 around this problem by operating at a high frequency in Ka band. Another 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. (Although this could be exploited to perform crude measurements of precipitation).

ARGOS Data Collection System
Main article: ARGOS (system)

It built by the French National Space Agency CNES. ARGOS contributes to the development and operational implementation of the global ARGOS Data Collection System. It will collect a variety of data from ocean buoys to transmit the same to the ARGOS ground segment for subsequent processing and distribution.

Solid State C-band Transponder (SCBT)

Is from ISRO and intended for ground RADAR calibration. It is a continuation of such support provided by C-Band Transponders flown in the earlier IRS-P3 and IRS-P5 missions.[1]

Applications
An artist's rendering of Satellite with ARgos and ALtiKa - SARAL

SARAL data products will be useful for operational as well as research user communities in many fields like[1]

  • Marine meteorology and sea state forecasting
  • Operational oceanography
  • Seasonal forecasting*
  • Climate monitoring
  • Ocean, earth system and climate research
  • Continental ice studies
  • Protection of biodiversity
  • Management and protection of marine ecosystem
  • Environmental monitoring
  • Improvement of maritime security

References
  1. "SARAL". Indian Space Research Organisation. Retrieved 2013-03-06.
  2. "Proposals Sought For Studying India-French Satellite Data". Spacemart.com. Archived from the original on 2010-01-07. Retrieved 2011-04-29.
  3. "ISRO successfully launches Indo-French satellite 'SARAL'". Zee News. 2013-02-25. Retrieved 2013-02-25.
  4. Peat, Chris (30 October 2013). "SARAL - Orbit". Heavens Above. Retrieved 31 October 2013.
  5. "Saral: Aviso". Aviso.oceanobs.com. 2008-06-02. Retrieved 2011-04-29.
  6. "Satellite SARAL". Ilrs.gsfc.nasa.gov. Archived from the original on 2012-07-05. Retrieved 2011-04-29.
  7. "Economic Times". Retrieved 2013-02-15.
  8. "India successfully launches Indo-French, 6 foreign satellites". Indian Express. 25 February 2013. Retrieved 25 February 2013.
  9. "eoPortal Directory". Directory.eoportal.org. 23 Feb 2007. Retrieved 2 May 2017.
  10. Steunou, N.; Desjonquères, J. D.; Picot, N.; Sengenes, P.; Noubel, J.; Poisson, J. C. (2015-09-10). "AltiKa Altimeter: Instrument Description and In Flight Performance". Marine Geodesy. Informa UK Limited. 38 (sup1): 22–42. doi:10.1080/01490419.2014.988835. ISSN 0149-0419.
  11. "GP - ALTIKA - Call for proposals until 15 February - CNES". Cnes.fr. 2010-01-18. Retrieved 2011-04-29.
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