Ocean Surface Topography Mission
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This article contains information regarding a satellite that is scheduled to launch in the next 8 days. Details may change as the countdown and ascent progress. Launch details: ULA will use a Delta II 7320 to launch OSTM (Jason-2) for NASA. Launch will occur from SLC-2W at VAFB. |
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The Ocean Surface Topography Mission (OSTM) on the Jason-2 satellite [1] is an international Earth observation satellite mission that will continue the sea surface height measurements begun in 1992 by the joint NASA/Centre National d’Etudes Spatiales (CNES) TOPEX/Poseidon mission [2] and now being made by the NASA/CNES Jason-1 mission launched in 2001.[3]
Like its two predecessors, OSTM/Jason-2 will use 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.
Scientists consider the 15-plus-year climate data record that this mission will extend critical for understanding how ocean circulation is linked to climate change and how global sea level, an important consequences and indicator of global climate change, is changing.
OSTM/Jason-2 is scheduled for launch in June 2008.[4] The spacecraft will be launched into a 1,336-kilometer (830-mile) circular, non-sun-synchronous orbit at an inclination of 66 degrees to Earth's equator, allowing it to monitor 95 percent of Earth's ice-free ocean every 10 days.
With OSTM/Jason-2, ocean altimetry makes the transition from research into operational mode. Responsibility for collecting these measurements will move from the space agencies to the world’s weather and climate forecasting agencies, which use them for short- and seasonal-to-long-range weather and climate forecasting.
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[edit] 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 with 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
[edit] 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 elec¬trons 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 centimeters (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.
[edit] Joint effort
OSTM/Jason-2 is a joint effort by four organizations.[5] The mission participants are:
- National Oceanic and Atmospheric Administration (NOAA)
- National Aeronautics and Space Administration (NASA)
- France’s Centre National d’Etudes Spatiales (CNES)
- European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT)
CNES is providing the spacecraft, NASA and CNES are jointly providing the payload instruments and NASA's Launch Services Program at the Kennedy Space Center is responsible for the launch management and countdown operations. After completing the on-orbit commissioning of the spacecraft, CNES will hand over operation and control of the spacecraft to NOAA. NOAA and EUMETSAT will generate the near-real-time products and distribute them to users. NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the mission for NASA's Science Mission Directorate, Washington.
[edit] Value of prior similar missions
The two previous altimetry missions TOPEX/Poseidon and Jason-1 have lead to major advances in the science of physical oceanography and in climate studies.[6] Their 15-year data record of ocean surface topography has provided the first opportunity to observe and understand the global change of ocean circulation and sea level. The results have improved the understanding of the role of the ocean in climate change and improved weather and climate predictions. Data from these missions are used to improve ocean models, forecast hurricane intensity, and identify and track large ocean/atmosphere phenomena such as El Niño and La Niña. The data are also used every day in applications as diverse as routing ships, improving the safety and efficiency of offshore industry operations, managing fisheries and tracking marine mammals.
Some of the areas in which TOPEX/Poseidon and Jason 1-have made major contributions, [7] and to which OSTM/Jason-2 will continue to add, are:
- Ocean Variability
The missions revealed the surprising variability of the ocean, how much it changes from season to season, year to year, decade to decade and on even longer time scales. They ended the traditional notion of a quasi-steady, large-scale pattern of global ocean circulation by proving that the ocean is changing rapidly on all scales, from huge features such as El Nino and La Nina, which can cover the entire equatorial Pacific, to tiny eddies swirling off the large Gulf Stream in the Atlantic.
- Sea Level Change
Measurements by TOPEX/Poseidon and Jason-1 show that mean sea level has been rising by about three millimeters (.12 inches) a year since 1993. This is about twice the estimates from tide gauges for the previous century, indicating a possible recent acceleration in the rate of sea level rise.
The data record from these altimetry missions has given scientists important insights into how global sea level is affected by natural climate variability, as well as by human activities.
- Planetary Waves
TOPEX/Poseidon and Jason-1 made clear the importance of planetary-scale waves, such as Rossby and Kelvin waves. No one had realized how widespread these waves are. Thousands of kilometers wide, these waves are driven by wind under the influence of Earth’s rotation and are important mechanisms for transmitting climate signals across the large ocean basins. At high latitudes, they travel twice as fast as scientists believed previously, showing the ocean responds much more quickly to climate changes than was known before these missions.
- Ocean Tides
The precise measurements of TOPEX/Poseidon’s and Jason-1 have brought knowledge of ocean tides to an unprecedented level. The change of water level due to tidal motion in the deep ocean is known everywhere on the globe to within 2.5 centimeters (one inch). This new knowl¬edge has revised notions about how tides dissipate. Instead of losing all their energy over shallow seas near the coasts, as previously believed, about one third of tidal energy is actually lost to the deep ocean. There, the energy is consumed by mixing water of different properties, a fundamental mechanism in the physics governing the general circulation of the ocean.
- Ocean Models
TOPEX/Poseidon and Jason-1 observations provided the first global data for improving the performance of the numerical ocean models that are a key component of climate prediction models.
[edit] Uses of altimetry data and benefits to society
Altimetry data have a wide variety of uses from basic scientific research on climate to ship routing. Applications include:
Climate Research: Altimetry data are incorporated into computer models to understand and predict changes in the distribution of heat in the ocean, a key element of climate.
El Niño & La Niña Forecasting: Understanding the pattern and effects of climate cycles such as El Niño helps predict and mitigate the disastrous effects of floods and drought.
Hurricane Forecasting: Altimeter data and satellite ocean wind data are incorporated into atmospheric models for hurricane season forecasting and individual storm severity.
Ship Routing: Maps of currents, eddies, and vector winds are used in commercial shipping and recreational yachting to optimize routes.
Offshore industries: Cable-laying vessels and offshore oil operations require accurate knowledge of ocean circulation patterns, to minimize impacts from strong currents.
Marine Mammal Research: Sperm whales, fur seals, and other marine mammals can be tracked, and therefore studied, around ocean eddies where nutrients and plankton are abundant.
Fisheries Management: Satellite data identify ocean eddies which bring an increase in organisms that comprise the marine food web, attracting fish and fishermen.
Coral Reef Research: Remotely sensed data are used to monitor and assess coral reef ecosystems, which are sensitive to changes in ocean temperature.
Ocean Debris Tracking: The amount of floating and partially submerged material, including nets, timber and ship debris, is increasing with human population. Altimetry can help locate these hazardous materials.
[edit] References
- ^ Ocean Surface Topography from Space. NASA/JPL.
- ^ Ocean Surface Topography from Space. NASA/JPL.
- ^ Ocean Surface Topography from Space. NASA/JPL.
- ^ NASA's Shuttle and Rocket Missions Launch Schedule. NASA.
- ^ (OSTM) - Jason 2 Overview. NOAA.
- ^ OSTM/JASON-2 SCIENCE AND OPERATIONAL REQUIREMENTS. EUMETSAT.
- ^ "The Legacy of Topex/Poseidon and Jason 1", page 30. Ocean Surface Topography Mission/Jason 2 Launch Press Kit, June 2008. NASA/JPL.
