OSTM/Jason-2, or Ocean Surface Topography Mission/Jason-2 satellite, was an international Earth observation satellite altimeter joint mission for sea surface height measurements between NASA and CNES. It was the third satellite in a series started in 1992 by the NASA/CNES TOPEX/Poseidon mission and continued by the NASA/CNES Jason-1 mission launched in 2001.
History Like its two predecessors, OSTM/Jason-2 used high-precision ocean altimetry to measure the distance between the satellite and the ocean surface to within a few centimeters. These very accurate observations of variations in sea surface height — also known as ocean topography — provide information about global sea level, the speed and direction of ocean currents, and heat stored in the ocean. Jason-2 was built by Thales Alenia Space using a Proteus platform, under a contract from CNES, as well as the main Jason-2 instrument, the Poseidon-3 altimeter (successor to the Poseidon and Poseidon 2 altimeter on-board TOPEX/Poseidon and Jason-1). Scientists consider the 15-plus-year climate data record that this mission extended to be critical to understanding how ocean circulation is linked to global climate change.
OSTM/Jason-2 was launched on 20 June 2008, at 07:46 UTC, from Space Launch Complex 2W at Vandenberg Air Force Base in California, by a Delta II 7320 rocket. The spacecraft separated from the rocket 55 minutes later.
It was placed in a 1,336 km (830 mi) circular, non-Sun-synchronous orbit at an inclination of 66.0° to Earth's equator, allowing it to monitor 95% of Earth's ice-free ocean every 10 days. Jason-1 was moved to the opposite side of Earth from Jason-2 and now flies over the same region of the ocean that Jason-2 flew over five days earlier. Jason-1's ground tracks fall midway between those of Jason-2, which are about 315 km (196 mi) apart at the equator. This interleaved tandem mission provided twice the number of measurements of the ocean's surface, bringing smaller features such as ocean eddies into view. The tandem mission also helped pave the way for a future ocean altimeter mission that would collect much more detailed data with its single instrument than the two Jason satellites did together. With OSTM/Jason-2, ocean altimetry made the transition from research into operational mode. Responsibility for collecting these measurements moved from the space agencies to the world's weather and climate forecasting agencies, which use them for short-range, seasonal, and long-range weather and climate forecasting.
Science objectives Extend the time series of ocean surface topography measurements beyond TOPEX/Poseidon and Jason-1 to accomplish two decades of observations Provide a minimum of three years of global ocean surface topography measurement Determine the variability of ocean circulation at decadal time scales from combined data record of TOPEX/Poseidon and Jason-1 Improve the measure of the time-averaged ocean circulation Improve the measure of global sea-level change Improve open ocean tide models
Ocean altimetry "Spaceborne radar altimeters have proven to be superb tools for mapping ocean-surface topography, the hills and valleys of the sea surface. These instruments send a microwave pulse to the ocean's surface and time how long it takes to return. A microwave radiometer corrects any delay that may be caused by water vapor in the atmosphere. Other corrections are also required to account for the influence of electrons in the ionosphere and the dry air mass of the atmosphere. Combining these data with the precise location of the spacecraft makes it possible to determine sea-surface height to within a few centimetres (about one inch). The strength and shape of the returning signal also provides information on wind speed and the height of ocean waves. These data are used in ocean models to calculate the speed and direction of ocean currents and the amount and location of heat stored in the ocean, which, in turn, reveals global climate variations".
Atomic clock synchronization Another payload aboard Jason-2 is the T2L2 (Time Transfer by Laser Link) instrument. T2L2 is used to synchronize atomic clocks at ground stations, and to calibrate the on-board clock of the Jason-2 DORIS instrument. On 6 November 2008, CNES reported the T2L2 instrument was working well.
Joint effort
OSTM/Jason-2 was a joint effort by four organizations. The mission participants were:
National Oceanic and Atmospheric Administration (NOAA) National Aeronautics and Space Administration (NASA) France's Centre national d'études spatiales (CNES) European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) CNES provided the spacecraft, NASA and CNES jointly provided the payload instruments, and NASA's Launch Services Program at the Kennedy Space Center was responsible for the launch management and countdown operations. After completing the on-orbit commissioning of the spacecraft, CNES handed over operation and control of the spacecraft to NOAA in October 2008. CNES processed, distributed, and archived the research-quality data products that became available in 2009. EUMETSAT processed and distributed operational data received by its ground station to users in Europe and archived that data. NOAA processed and distributed operational data received by its ground stations to non-European users and archived that data along with the CNES data products. NOAA and EUMETSAT both generated near-real-time data products and distributed them to users. NASA evaluated the performance of the following instruments: the Advanced Microwave Radiometer (AMR), the Global Positioning System payload, and the Laser Retroreflector Assembly (LRA). NASA and CNES also validated scientific data products together. NASA's Jet Propulsion Laboratory in Pasadena, California, managed the mission for NASA's Science Mission Directorate in Washington, D.C.
Prior similar missions
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