What is Jason-3?

                 

Jason-3 is a satellite mission that supports scientific, commercial and practical applications related to sea level rise, ocean circulation, and climate change. Jason-3 follows the current operational altimeter satellite, Jason-2, in maintaining satellite altimetry observations of global sea surface height. Jason-3 is an international cooperative mission in which NOAA is partnering with the Centre National d'Etudes Spatiales (CNES, France’s governmental space agency), European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), and National Aeronautics and Space Administration (NASA).

Jason-3 will make highly detailed measurements of sea surface height, which is a measure used to study sea level rise—a critical factor in understanding Earth’s dynamic climate. Sea surface height data from altimetry satellites like Jason-3 are also used to study hurricane intensity, tsunami dynamics, El Niño Southern Oscillation, eddy dynamics, ocean boundary currents, coastal and shallow water tides, as well as weather and climate forecasting.

Orbit

In what orbit will Jason-3 fly?

To ensure continuity of the global sea level record, Jason-3 will fly in the same 9.9 day repeat track orbit as all previous Jason missions, meaning the satellite will make observations over the same ocean point once every 9.9 days. The orbital parameters are: 66.05 degree inclination, 1380 km apogee, 1328 km perigee, 112 minutes per revolution around the earth.

One of the primary objectives of the Jason program is to monitor sea level rise, a challenging task considering the need to maintain high levels of accuracy and precision from one satellite to the next over multiple decades of time. One way to help reach this goal is to avoid gaps in the data record by launching each new Jason satellite while the older Jason satellite is still operating properly. In the first six months after launch, Jason-3 will be flown one minute behind Jason-2/OSTM, in order to detect any offsets between the missions. Subsequently, Jason-2/OSTM will be moved to different 9.9 day orbit to provide additional data coverage.

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Why does Jason-3 carry different orbit determination instruments?

We need to know the orbit height of the satellite as it revolves around Earth very precisely, to within 1 centimeter (0.4 inch), in order to detect sea level change. Combining measurements from three different techniques (GPS, DORIS, laser ranging), each with their own strengths, provides more precise orbit determination than using a single method.

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How does Jason-3 use GPS?

Jason-3’s Global Positioning System Payload receiver is used to complement two other instruments on board Jason 3 that provide accurate measurements of the satellite’s location in orbit. The GPS receiver on Jason 3 uses data from the constellation of GPS satellites in orbit to constantly determine its position in orbit.

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How much will Jason-3 weigh and what are its dimensions?

Jason-3 is a relatively small satellite by today’s standards, weighing only about 510 kilograms (1,124 pounds). After the solar panels are deployed, Jason-3 will be roughly the size of a minivan: 1 meter by 1 meter by 3.7 meters (3.3 feet by 3.3 feet by 12.1 feet).

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Data Collection

What is “satellite altimetry”? How does satellite altimetry work?

Satellite altimetry is a technique that uses orbiting spacecraft to make very accurate measurements of the height of Earth's land, ice and ocean. Jason-3 carries a radar altimeter system specially designed to make extremely accurate and precise measurements of the height and waves of the ocean surface. Each second, the Jason-3 altimeter bounces thousands of radar pulses off of the sea surface, while a radiometer measures how the radar waves are slowed by the atmosphere and three additional instruments help measure the satellite's precise orbit.

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How Radar Altimetry Works

How satellite altimetry works (Credit: NOAA/NESDIS STAR)

What kind of measurements will Jason-3 take?

Jason-3 is designed to measure sea level, as well as wave height and ocean surface wind speeds globally, every 10 days. There are three measurement systems onboard Jason-3: (1) a radar altimeter that measures the range between the satellite and the sea surface, (2) orbit determination systems (e.g., GPS) that measure the height of the satellite relative to the earth’s center of mass, and (3) a microwave radiometer. The difference between the orbit height and altimeter range measurements provides the fundamental measurement of sea surface height. In addition, the altimeter provides wave height and ocean surface wind speed measurements. The radiometer data are used to correct the altimeter range measurements for the presence of atmospheric water vapor.

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What is “ocean surface topography”?

Ocean surface topography is the measurement of height variations in the surface of the sea. Similar to how winds blow around the highs and lows of atmospheric pressure, ocean currents flow around the highs and lows of ocean topography. Ocean surface topography is caused by ocean waves, tides, currents, the atmosphere and the amount of heat the ocean holds. Observations of ocean surface topography are used to help to understand and predict short-term changes in weather and longer-term climate patterns..

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SSH-data

This image shows the average sea surface height data from 2012. Areas colored blue are higher than normal (base period 1993-2012); areas colored brown are lower than normal.

How are the data taken by altimetry satellites different from data taken by NOAA’s POES and Suomi NPP satellites?

The Jason missions provide a uniquely different kind of information from the other NOAA satellite missions (GOES and Suomi NPP). Jason satellites measure the surface topography of the ocean, producing a complete global grid of sea level observations every 10 days. These measurements are used by oceanographers to map the major currents (e.g., Gulf Stream), as well as smaller scale, turbulent “eddy” motions in the ocean, sometimes referred to as ocean “weather.”

The same observations averaged over a month or longer time interval also provide a way of monitoring global and regional sea level rise. More than 90 percent of the extra heat trapped in the Earth system by the greenhouse phenomenon is stored in the ocean, causing the ocean to expand and sea level to rise. Jason observations also provide a way of estimating the increase in ocean volume caused by the melting of mountain glaciers and the Antarctic and Greenland ice sheets. This information is used by scientists and government agencies to develop long-range projections and ultimately for coastal planning purposes.

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What are the advantages of satellite altimetry data over other ocean data?

Data from the Jason series of satellites provide more accurate measurements of local sea level changes than previous satellites and other tools. Jason satellites are equipped with altimeters, used to measure the altitude above a fixed location. The Jason altimeters measure sea level over the entire global ocean and therefore provide information at specific locations, along coastlines and across all the ocean basins.

The continuous altimeter record from Jason satellites also provides essential information for understanding regional sea level change. Coupled with coastal observation systems, the regional granularity of the sea level change signal allows a better understanding of the local impacts of sea level rise. For instance, researchers are integrating nearshore altimeter data with tide gauge data to construct regional climate indicators for sea level change.

Satellite altimeters have another advantage for measuring sea level. While tide gauges also measure sea level, and can do so with the precision of a few millimeters, researchers attach them to land. Due to geological and hydrological changes, land is subject to vertical motions of up to a few millimeters per year, making the sea level measurements difficult to use in monitoring changes of absolute sea level. Jason carries instruments designed to minimize the potential variability in measurements of sea level between tide gauges. Most importantly, because the tide gauge network is sparse and land-based, only altimeters can provide nearly global coverage of local changes in sea level measurements. These global observations are crucial to monitoring and interpreting the processes that produce local changes in sea level.

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Applications

Who will be the key users of Jason-3 data?

The primary users of Jason-3 data fall mainly into two broad categories: (1) users reliant on marine and weather forecasts for public safety, commerce and environmental purposes, and (2) scientists and long-range planners concerned with global warming and its impact on the ocean.

NOAA and EUMETSAT are using the data primarily for operational applications in the first category, while NASA and CNES are focusing on research applications.

More specifically, NOAA and EUMETSAT will be using the data for monitoring of wind and waves on the high seas, hurricane intensity forecasting, modeling of ocean surface currents, El Niño forecasts, monitoring of lake and river levels, and, at the longest time scales, climate monitoring.

NASA and CNES intend to use the Jason data as a critically important source of information for understanding and planning for climate change. More than 90% of the surplus heat associated with global warming trends is going into the ocean, causing sea level rise and a wide range of ecological changes that scientists and managers are trying to come to grips with.Ultimately, however, the benefits of Jason-3 data will transfer to people and to the economy. El Niño events , for example, are known to cause droughts and flooding conditions in different parts of the US, so farmers will benefit from forecasting of these events.

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What are the weather and climate applications of Jason-3 data?

Weather forecasting, both atmospheric and oceanic, is an initial-value problem—you must get the initial condition correct to get the forecast correct, which is why operational modeling systems spend so much time and energy on data assimilation. Researchers assimilate data from Jason satellites into ocean and coastal models to improve the models’ ability to predict oceanographic conditions. In the ocean, sea surface height, measured by altimetry, is a key indicator of strong and variable currents at and below the surface, like the Gulf Stream and its associated meanders and eddies.

Studies have shown that leaving out altimetry data, especially Jason-2 data (a data record Jason-3 will continue), strongly degrades a model's ability to simulate these mesoscale ocean features (see, e.g., http://www.marine.csiro.au/~oke060/PUBS/Lea-2013.pdf ). These often are the very features that have the strongest effects on ocean operations such as ocean drilling, wind energy siting, military applications and on fishing success. Ocean forecasting without altimetry would be roughly analogous to weather forecasting without radar data, that is, without the means to identify operationally critical mesoscale features like squall lines and thunderstorm cells. Individuals can use these models for a variety of requirements, including ecological prediction, marine transportation and fisheries management. The National Ocean Service is now developing a model for the west coast with this capacity in order to improve model skill.

Jason satellites provide the core measurements used for the Intergovernmental Panel on Climate Change for global sea level rise, pattern of sea level rise and sea level budget. It also contributes to understanding the global heat budget and changes in winds and waves. State and local authorities have used these sea level rise products for climate assessments and planning.

Additionally, scientists and administrators use Jason data in a variety of high-visibility and high-impact reports, assessments and publications, including:

  • Annual State of the Climate developed by NOAA’s National Climatic Data Center, now a part of the National Centers for Environmental Information
  • Climate Change Indicators developed by the U.S. Environmental Protection Agency
  • Coastal Impacts, Adaptation, and Vulnerabilities Technical Inputs Report to the National Climate Assessment, co-authored by Margaret Davidson (NOAA) and Virginia Burkett (U.S. Geological Survey)
  • Sea level budget produced by NOAA’s Laboratory for Satellite Altimetry

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How will data from the Jason satellite series be used in hurricane forecasting and modeling?

Altimetry data from these satellites can be used to infer ocean heat content, which is a very important factor for hurricane intensity change. Sea surface temperature plays a role, but is only a "skin temperature." Hurricanes, and particularly strong or slow-moving hurricanes, tend to mix the ocean very effectively, so if the warm water at the surface does not extend down very far, a hurricane can actually kill itself off by bringing up cold water under itself and constraining its energy source. Ocean heat content is generally understood to be a more useful predictor of hurricane intensity change than sea surface temperature alone.

We use Jason data to analyze and predict extreme waves in hurricanes as well as large wind waves/swell produced by other phenomenon.

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Hurricane-Arthur

Imagery of Hurricane Arthur taken by NOAA's GOES East satellite on July 3, 2014.

Are data still being used from previous Jason missions?

Yes, data from the older missions are used in many important operational and research related activities. For example, NOAA uses observations made during old hurricane events to help improve current hurricane forecasting models. The older data are also essential for determining regional and global rates of sea level change and any accelerations that may take decades to become apparent. It is important to note that the older data sets are being continuously improved with better corrections and processing techniques, thus making them more valuable with time.

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What have scientists learned overall about the environment based on data from the Jason/OSTM missions?

By far the most important result coming out the Jason missions to date is the knowledge that global average sea level is now rising twice as fast as it did over the past century, providing clear evidence of global warming. The Jason missions also reveal that this change is not occurring uniformly over the ocean. For example, the western tropical Pacific Ocean is now rising faster than the average rate, while the northeastern Pacific Ocean is actually falling slightly. The Jason results, combined with measurement from two other observing systems— NASA and the German Aerospace Center’s joint Gravity Recovery And Climate Experiment (GRACE), another satellite that measures changes in Earth’s gravity field, and Argo, an array of drifting ocean profiling instruments that measures changes in ocean density—have made it possible to determine the actual causes of sea level rise. We now know that two-thirds is caused by the addition of ice melt water coming from mountain glaciers and the ice sheets of Antarctica and Greenland and one-third is due to expansion caused by ocean warming.

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Why is maintaining long-term records of sea surface height important?

Climate change is the combination of many complex processes happening on many different time scales. An example of natural decadal variability is the El Niño/La Niña phenomenon centered on the tropical Pacific Ocean. At longer time scales, global warming due to human activity and the greenhouse effect is the dominant process. In order to distinguish between the different time scales and processes that can contribute to sea level rise, and especially to determine if sea level rise is accelerating, it is critically important to have a long, continuous, global record of sea surface height … exactly what Jason-3 and the other Jason altimeter missions are designed to provide.

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History and Future of Altimetry Missions

Who is Jason?

The Jason program is named after the ancient Greek mythological hero Jason, who led the Argonauts of the ship Argo on a quest to find the Golden Fleece.

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Jason and the Argonauts

Jason and the Argonauts Disembark at Colchis, Charles de la Fosse, Palace of Versailles, Salon of Diana. (Coyau / Wikimedia Commons)

How is Jason-3 different from Jason-2, Jason-1 and the original NASA/CNES TOPEX/Poseidon mission?

Jason-3 will maintain the nation’s satellite altimetry observations of global sea surface height that began in 1992 with the TOPEX/Poseidon mission. Jason-3 is the follow-on to the Ocean Surface Topography Mission on the current operational altimeter satellite, Jason-2. It will inherit the main features of Jason-2, including orbit, instruments and measurement accuracy.

The TOPEX/Poseidon mission, which launched in 1992, was a joint mission between NASA and CNES to measure ocean surface topography. It had on-board two altimeters, the TOPEX and the Poseidon, which shared an antenna. Jason-1 was the successor mission and operated with one altimeter, the Poseidon-2, upgraded from the Poseidon altimeter.

Named the Ocean Surface Topography Mission, Jason-2 was the follow-on mission to Jason-1, this time with EUMETSAT and NOAA included as partners. Jason-2 flies a Poseidon-3 altimeter and an Advance Microwave Radiometer, an enhanced version of the radiometer on-board Jason-1.

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Is Jason-2 still operational?

Launched in 2008, Jason-2 is still operating successfully after 7 years, with nearly all primary and backup systems fully functional. Jason-2 will continue providing additional data coverage after Jason-3 is operational.

How long do the Jason satellites last?

The first three Jason satellites (Jason-1, Jason-2/OSTM, Jason-3) were engineered and built identically to each last five years. Jason-1 operated for 11 years (2001 to 2013), although with degraded performance in the last few years. Jason-2/OSTM, launched in June 2008, continues to operate successfully after nearly seven years in orbit.

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Which agencies are involved in the Jason-3 mission and what are their respective roles?

Jason-3 continues a long history of productive transatlantic cooperation in environmental satellites. This particular mission is supported by a partnership of NOAA, NASA, the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT), and the French Space Agency (CNES).

NOAA and EUMETSAT lead the overall program, and share responsibilities for operating the satellite and processing its data. NOAA also was responsible for providing launch services, microwave radiometer, and precision orbit determination components (e.g., GPS, LRA). EUMETSAT provides the spacecraft, altimeter, and additional precision orbit components. CNES is making a significant in-kind contribution to the program and will act at the technical level as the system coordinator. NASA, in conjunction with the three other partners, will support science team activities and serves as space segment acquisition and development agent for the NOAA provided instruments and launch services.

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Do the four agencies involved in the Jason-3 mission have a history of cooperation?

Yes, Jason-3 continues a transatlantic partnership in space-based altimetry dating back to 1992, when NASA and CNES teamed up to launch the TOPEX/Poseidon mission. NASA and CNES continued this measurement with the launch of Jason-1 in 2001. NOAA and EUMETSAT joined NASA and CNES to continue this measurement with the launch of OSTM/Jason-2 in 2008, and have partnered again for Jason-3.

Furthermore, all four agencies have a rich history of productive, cooperation beyond altimetry missions. NOAA and EUMETSAT in particular have a 30-year history of cooperation in polar-orbiting and geostationary meteorological satellites.

NOAA and CNES have other long-standing cooperative programs in addition to ocean altimetry.

  • Argos is a data collection and location relay system administered under an agreement between NOAA and CNES initiated in 1974. Today, CNES sensors fly on NOAA, EUMETSAT, and ISRO satellites.
  • COSPAS-SARSAT is an international satellite-aided search and rescue system that is been credited with saving over 35,000 lives since 1982. The governing parties of the system are the U.S. (NOAA), France (CNES), Russia (Morsviazsputnik), and Canada (National Search-and-Rescue Secretariat). NOAA provides space on its polar-orbiting satellites for French processors and Canadian receivers.

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How much did each agency contribute to the cost of Jason-3?

The life cycle cost of Jason-3 for NOAA amounts to $177M. NASA’s funding is provided by NOAA. The EUMETSAT contribution including the funding from the European Commission for operation amounts at 110 M€ ($119M in current economic conditions). The CNES contribution amount for Jason-3 is at 63 M€ ($68M in current economic conditions).

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Jason in the cleanroom

Jason-3 undergoing thermal testing which recreates conditions that the satellite will meet in space. Credit: Rémy Decourt, Futura-Sciences

After Jason-3, what’s next?

The international partners are considering development of a newly engineered series of radar altimeter satellites, Jason-CS, to be flown in the 2020s. As with earlier missions, Jason-CS would be jointly supported by the US and Europe. The new satellites, also known as Sentinel-6/Jason-CS missions in Europe, would be capable of measuring sea level more precisely than previous Jason missions and would have a longer design life of seven years.

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