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NASA - Overview
May 14, 2008

artist concept of Ocean Surface Topography Mission The Ocean Surface Topography Mission (OSTM)/Jason-2 is an international satellite mission that will extend into the next decade the continuous climate record of sea surface height measurements begun in 1992 by the joint NASA/Centre National d'Etudes Spatiales (CNES) Topex/Poseidon mission and continued in 2001 by the NASA/CNES Jason-1 mission. This multi-decadal record has already helped scientists study global sea level rise and better understand how ocean circula-tion and climate change are related.

Developed and proven through the joint efforts of NASA and CNES, high-precision ocean altimetry measures the distance between a satellite and the ocean surface to within a few centimeters. Accurate observations of variations in sea surface height-also known as ocean topography-provide scientists with information about the speed and direction of ocean cur-rents and heat stored in the ocean. This information, in turn, reveals global climate variations.

With OSTM/Jason-2, ocean altimetry has come of age. The mission will serve as a bridge to transition collection of these measurements to the world's weather and climate forecasting agencies, which will use them for short- and seasonal-to-long-range weather and climate forecasting.

Sea level rise is one of the most important consequences and indicators of global climate change. From Topex/Poseidon and Jason-1 we know mean sea level has risen by about three millimeters (0.12 inches) a year since 1993. This is about twice the estimates from tide gauges for the previous century, indicating a possible recent acceleration. OSTM/Jason-2 will further monitor this trend and allow us to better understand year-to-year variations.

The speedup of ice melting in Greenland and Antarctica is a wild card in predicting future sea level rise. Measurements from Jason-1 and OSTM/Jason-2, coupled with informa-tion from NASA's Gravity Recovery and Climate Experiment (Grace) mission, will provide crucial information on the rela-tive contributions of glacier melting and ocean heating to sea level change.

Earth's oceans are a thermostat for our planet, keeping it from heating up quickly. More than 80 percent of the heat from global warming over the past 50 years has been absorbed by the oceans. Scientists want to know how much more heat the oceans can absorb, and how the warmer water affects Earth's atmosphere. OSTM/Jason-2 will help them better calculate the oceans' ability to store heat.

The mission will also allow us to better understand large-scale climate phenomena like El Niño and La Niña, which can have wide-reaching effects.

OSTM/Jason-2 data will be used in applications as diverse as, for example, routing ships, improving the safety and efficiency of offshore industry operations, managing fisheries, forecast-ing hurricanes and monitoring river and lake levels.

OSTM/Jason-2's primary payload includes five instruments similar to those aboard Jason-1, along with three experimental instruments. Its main instrument is an altimeter that precisely measures the distance from the satellite to the ocean surface. Its radiometer measures the amount of water vapor in the atmosphere, which can distort the altimeter measurements. Three location systems combine to measure the satellite's precise position in orbit. Instrument advances since Jason-1 will allow scientists to monitor the ocean in coastal regions with increased accuracy, almost 50 percent closer to coastlines that are home to nearly half of Earth's population than before. OSTM/Jason-2 is designed to last at least three years.

After its launch from California's Vandenberg Air Force Base aboard a United Launch Alliance Delta II rocket, OSTM/Jason-2 will be placed in the same orbit (1,336 kilometers) as Jason-1 at an inclination of 66 degrees to the equator. It will repeat its ground track every 10 days, covering 95 percent of the world's ice-free oceans. A tandem mission with Jason-1 will further improve tide models in coastal and shallow seas and help scientists better understand the dynamics of ocean currents and eddies.

OSTM/Jason-2 is a collaboration between NASA; the Na-tional Oceanic and Atmospheric Administration (NOAA); CNES; and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). CNES is provid-ing 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 Delta II launch management and countdown operations. After completing the on-orbit commissioning of the spacecraft, CNES will hand over its operation and control 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 in Washington.

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