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Altimeter missions considered in GlobWave

ERS-1

ERS-1 small Mission : ERS-1
Agency : ESA
Coverage : 01 Feb 1992 – 02 Jun 1996

 Overview : The ERS Program (European Remote Sensing satellite system) of the European Space Agency is one of the most essential part of an important european earth observation program concerning : meteorology, climatology, oceanography, land resource management...ERS-1 was the first of two twin earth observing satellites launched by ESA respectively in July 1991 and April 1995. It included, in addition to other instruments, several sensors relevant for oceanography such as the RA radar altimeter (measurement of the sea surface topography, the wave height,...), the AMI-Wind scatterometer (measurement of the surface wind speed and direction over the ocean), the SAR (measurement of wave spectra) and the MW micro-wave sounder (brightness temperature, atmospheric vapour content,...). The ERS-1 mission ended on 10th March 2000 (its sensors had been on stand-by since 1995). ERS-1 and ERS-2 altimeters operate in Ku band (13.8 GHz).

ERS-2

ERS-2 small Mission : ERS-2
Agency : ESA
Coverage : 15 May 1995 – 22 June 2003

Overview : The ERS Program (European Remote Sensing satellite system) of the European Space Agency is one of the most essential part of an important european earth observation program concerning : meteorology, climatology, oceanography, land resource management...ERS-1 was the 2nd of two twin earth observing satellites launched by ESA respectively in July 1991 and April 1995. It included, in addition to other instruments, several sensors relevant for oceanography such as the RA radar altimeter (measurement of the sea surface topography, the wave height,...), the AMI-Wind scatterometer (measurement of the surface wind speed and direction over the ocean), the SAR (measurement of wave spectra) and the MW micro-wave sounder (brightness temperature, atmospheric vapour content,...). Despite a reduced coverage since the failure of an onboard recorder in 2001, and an initially expected lifetime of three years, it is still operational. ERS-1 and ERS-2 altimeters operate in Ku band (13.8 GHz).

ENVISAT

Envisat small Mission : Envisat
Agency : ESA
Coverage : 26 Aug 2002 - 8 April 2012

Overview : Envisat, a follow-on to ERS series, is the largest Earth Observation spacecraft ever built. Onboard instruments relevant for oceanography include an Advanced Synthetic Aperture Radar (ASAR) providing measurement of sea surface (wind, wave spectra, roughness), a imaging spectrometer (MERIS) providing ocean color data and an Advanced Along Track Scanning Radiometer (AATSR) providing measurement of sea surface temperature. The Envisat RA2 Altimeter is based on the heritage of ERS-1 RA functioning at the main nominal frequency of 13.575 GHz (Ku Band), and also 3.2 GHz (S band).

Topex / Poseidon

TOPEX-POSEIDON small Mission : Topex/POSEIDON
Agency : CNES/NASA
Coverage : 25 Sep 1992- 08 Oct 2005

Overview : The Topex/Poseidon satellite was launched on 10 August 1992 with the objective of "observing and understanding the ocean circulation". A joint project between NASA, the US space agency, and CNES - the French space agency - it carried two radar altimeters and precise orbit determination systems, including the DORIS system. On 15 September 2002 Topex/Poseidon assumed a new orbit midway between its original ground tracks. The former Topex/Poseidon ground tracks are now overflown by Jason-1. This tandem mission demonstrated the scientific capabilities of a constellation of optimised altimetry satellites. The last data were acquired on October 2005, due to a failure in a pitch reaction wheel. The mission ended on 18 January 2006. The Poseidon altimeter operates at two frequencies (13.6 GHz in the Ku band and 5.3 GHz in the C band) to determine atmospheric electron content, which affects the radar signal path delay. These two frequencies also serve to measure the amount of rain in the atmosphere. The Poseidon instrument was first embedded onboard Topex/Poseidon mission, but two new versions - Poseidon-2 and Poseidon-3 - were derived for respectively Jason-1 and Jason-2 missions.

Jason-1

Jason-1 small Mission : Jason-1
Agency : CNES/NASA
Coverage : 15 Jan 2002 - onwards

Overview : Jason-1 is a joint french/american follow-on to the successful TOPEX/Poseidon mission. It provides precise sea surface height measurements (within 2 cm accuracy) in order to support operational oceanography at modelling and forecasting ocean circulation, currents, water temperature,... and to monitor sea level change at climatological scale. Sea surface height, wave height or wind speed can be measured by the onboard radar altimeter, complemented by additional instruments for improved atmospheric and orbit correction. Poseidon-2 is the mission's main instrument, derived from the experimental Poseidon-1 altimeter on Topex/Poseidon. It is a compact, low-power, low-mass instrument offering a high degree of reliability. Poseidon-2 is a radar altimeter that emits pulses at two frequencies (13.6 GHz in the Ku band and 5.3 GHz in the C band) (Instrument supplied by CNES)

Jason-2

JASON-2 small Mission : Jason-2
Agency : CNES/NASA
Coverage : 01 Dec 2008 - onwards

Overview : Jason-2 is a Low Earth Orbiting (LEO) satellite that measures sea surface height with high precision on an operational basis, and is an essential component of the global ocean-observing systems. Jason-2 is placed into the same non-sun-synchronous orbit as Jason-1, at an altitude of 1336 kilometres, inclined 66 degrees, to provide virtually complete coverage of ice-free oceans. With a global data coverage between 66°N and 66°S latitude and a 10-day repeat of the ground track (±1-km accuracy), Jason provides coverage of 95% of ice-free oceans every 10 days. Poseidon-3 is the mission's main instrument, derived from the Poseidon-2 altimeter on Jason-1 and using the two same frequencies (Instrument supplied by CNES).

GEOSAT

GEOSAT small Mission : GEOSAT
Agency : US Navy
Coverage : 31 Mar 1985 - 30 Dec 1989

Overview : Geosat (GEOdetic SATellite) was launched in March 1985, and ended its mission in January 1990. Its primary task was to measure the marine geoid for the US Navy, but it also provided measurements of sea state and winds which proved to be useful for operational Navy purposes. Once this 18-month mission was over, the satellite was put on a 17-day repeat orbit (Exact Repeat Mission: ERM) which began on 8 November 1986, retracing Seasat's ground tracks, and providing the scientific community, through NOAA, with altimeter data for over three years. Geosat was the first mission to provide long-term high-quality altimetry data. The Geosat radar altimeter operates at a frequency of 13 GHz.

GEOSAT Follow-On (GFO)

GFO-Satellite small Mission : GEOSAT Folow-On
Agency : US Navy
Coverage : 08 Jan 2000 - 23 Jul 2008

Overview : GFO, Geosat Follow-On was launched in February 1998, and retired in November 2008. Its mission was to provide real-time ocean topography data to the US Navy. Scientific and commercial users have access to these data through NOAA (National Oceanic and Atmospheric Administration). Its primary payload was a radar altimeter. GFO had the same 17-day repeat period orbit as the Geosat "Exact Repeat Mission" (800 km altitude). The GFO Radar Altimeter used a single frequency (13.5 GHz) with 3.5-cm height precision.