Glossary

Infrared imaging instrument onboard Envisat, used to study sea-surface temperatures. Follow-on from ATSR-1 and ATSR-2 on board ERS-1 and ERS-2. Data are derived from measurements of reflected and emitted radiation taken at several wavelengths.

Cold current encircling the Antarctic, driven by westerly winds between 40° and 50° South. The flow of the ACC is not checked by the continents. It thus links the Atlantic, Indian and Pacific Oceans.

Sea surface height with respect to the geoid. Absolute dynamic topography is the sum of the Mean Dynamic Topography and of the Sea Level Anomalies. ADT = MDT+SLA = SSH - geoid

AGU is a scientific society that aims to advance the understanding of Earth and space. AGU conducts meetings and conferences, publishes journals, books and a weekly newspaper, and sponsors a variety of educational and public information programs.

Along-track data are data chronologically ordered, following the satellite "ground track", i.e. the virtual track left by the radar beam on the ground.

Amma is an international multidisciplinary program which was initiated to gain better understanding of the reasons beahind disturbances to the African monsoon.

The Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) is a twelve-channel, six-frequency, passive-microwave radiometer system. It measures horizontally and vertically polarized brightness temperatures at 6.9 GHz, 10.7 GHz, 18.7 GHz, 23.8 GHz, 36.5 GHz, and 89.0 GHz. Spatial resolution of the individual measurements varies from 5.4 km at 89 GHz to 56 km at 6.9 GHz.

AMSR-E is an instrument onboard Aqua Satellite (Nasa)

Argo is a global array of 3,000 free-drifting profiling floats that measures the temperature and salinity of the upper 2000 m of the ocean.  This allows, for the first time, continuous monitoring of the temperature, salinity, and velocity of the upper ocean, with all data being relayed and made publicly available within hours after collection.

Forecasting model used by the French weather service Météo-France.

Ascii data are data stored in a text format (wrt binary data, which need to be read by binary/hexadecimal editors, or specific programs).
 Ascii data are somehow easier to read without background software, but give much heavier files than binary.

Instrument flown on Noaa satellites that measures sea-surface temperatures. The AVHRR instrument operates in the infrared waveband.

Aviso distributes satellite altimetry data from Topex/Poseidon, Jason-1, ERS-1 and ERS-2, and EnviSat, and Doris precise orbit determination and positioning products.

Doris/Poseidon control center

Instruments control center

French research center on black tides and water pollution.

European Center for Research and Advanced Training in Scientific Computation

The Center for Satellite Exploitation and Research (CERSAT) is one of the major world data centers for oceanography. It processes, archives and distributes a large amount of data products obtained from satellite remote-sensing, mostly intended to support research activity in various fields (oceanography, meteorology, climatology,...) and operational applications based on space data.

The COARDS format is a convention for the standardization of NetCDF (data format) files.

It is sponsored by the "Cooperative Ocean/Atmosphere Research Data Service ", a NOAA/university cooperative for the sharing and distribution of global atmospheric and oceanographic research data sets.

The CF (Climate and Forecast) conventions generalize and extend the COARDS conventions. The extensions include metadata that provides a precise definition of each variable. This standard also relaxes the COARDS constraints on dimension order and specifies methods for reducing the size of datasets.

gravimetric satellite (GFZ/DLR)

WCRP program

Founded in 1986, CLS is a subsidiary of Cnes and Ifremer, specialized in satellite-based data collection, location and ocean observations by satellite.

altimetric multi-mission center. Processing center for altimetry missions (Jason-1, Envisat...)

The Centre National d'Etudes Spatiales is a French industrial and commercial institution founded in 1961, in charge of the French space policy.

The Centre National de la Recherche Scientifique (CNRS) is the leading research organization in France covering all the scientific, technological and societal fields.

Member of a research group that is part of a science team (e.g. Ocean Surface Topography Science Team)

This format is a convention for the standardization of NetCDF (data format) files. 

It is sponsored by the "Cooperative Ocean/Atmosphere Research Data Service ", a NOAA/university cooperative for the sharing and distribution of global atmospheric and oceanographic research data sets.

The CF conventions generalize and extend the COARDS conventions. The extensions include metadata that provides a precise definition of each variable. This standard also relaxes the COARDS constraints on dimension order and specifies methods for reducing the size of datasets.

The Commonwealth Scientific and Industrial Research Organisation is Australia's national science agency with 16 scientific divisions included the Oceans and Coasts division.

Type of oceanography probe for measuring temperature and salinity

Jason's (and T/P's) is almost 10 day long. Envisat's 35 days.

Use of data as initial input to a model and during computation to yield results that fit/approximate reality as closely as possible. For example, assimilation of readings from meteorology stations into weather forecasting models generates more reliable results.

Antennas on the ground receive raw telemetry from satellites. These raw data must be processed by applying corrections and combining them with complementary data before they are usable. Data are processed to different levels:
Level 0: raw telemetry
Level 1: time-tagged data located and corrected for perturbing effects (level 1, 1.5 and 1b data fall into this category)
Level 2: geophysical data (GDR-M) time-tagged, precisely located and corrected for environment effects. Data at this level are used by specialists with a close knowledge of their subject.
Level >2: data ready for immediate use in applications.
level 3: data after validation processes. Some data are removed, due a quality deemed insufficient or due to inadequacity to the surface (e.g. lake data for ocean products). Cross-calibration processes can also be applied, to merged different satellites' data
level 4: gridded data (regular or irregular grid)
Depending on the mission, retracking is performed at level 1 or 2.

Real-time onboard Doris system to compute orbit

German Aerospace Center

(or Doppler-Fizeau effect for electromagnetic waves)
The pitch of a sound emitted by a moving object appears to be higher the faster it approaches, and lower the faster it moves away. A good analogy is a stream into which leaves are thrown at regular intervals. As we move upstream towards the source, leaves will flow past us more often. The faster we go, the more leaves we will see. Conversely, as we move downstream away from the source leaves will flow past less often-to the point where we would only see a single leaf when moving at the same speed as the current.
High-pitched sounds have high frequencies, which means we "meet" the sound wave often-as if we were moving towards the source (or it was approaching us); low-pitched sounds have lower frequencies-as if we were moving away. The same principle applies to light rays, which shift towards the longer wavelengths as they move away, and towards the shorter wavelengths as they approach. (Adapted from Evry Schatzmann, Les Enfants d'Uranie)
We can thus determine the velocity of a moving object emitting sound or light waves by measuring the shift between the transmitted and received frequencies. The Doris system achieves precise orbit determination and location by measuring the Doppler shift in this way.

Permanent gases in the atmosphere (oxygen, nitrogen) slow the radar pulse, generating an error on altimetry measurements of the order of 2.30 meters. The value of the correction is determined from atmospheric pressure data supplied by a meteorological model.

Data produced from the GDR, using the best quality orbit.

This system processes data from all altimeter missions (Jason-1, T/P, Envisat, GFO, ERS-1 & 2 and even Geosat) to provide a consistent and homogeneous catalogue of products for varied applications, both for near real time applications and offline studies.

Sea level driven by thermodynamic processes in the ocean

Hydrodynamic instabilities in the oceans that form in the wake of currents or are generated by winds. Eddies may persist for weeks or months, and may be tens to hundreds of kilometers across. They penetrate quite deep below the ocean surface and transport heat, salts and nutrients.

Perturbation of the altimeter radar pulse due to the fact that wave troughs reflect more energy than wave crests.

 Climatic phenomenon occurring in the Tropics that involves transports of warm (El Niño) or cold (La Niña) water masses from west to east across the Pacific basin. This displacement of water is accompanied by a shift of atmospheric cells, and therefore of winds and monsoons across the Tropics. This oscillation, which has been occurring at irregular intervals for thousands of years, has a global effect on climate. The phenomenon is named "El Niño" (meaning the Christ Child or the Little Boy in Spanish) because warm waters often reach the coast of Peru around Christmas time, often severely disrupting local fisheries.

The radar pulse used to measure altimetry is subjected to a number of disturbances as it passes through the atmosphere and when it is reflected by the sea surface.

Earth-observing satellite (Esa)

Phase of the Geosat mission during which the satellite was put into a 17-day repeat orbit to study the oceans.

Earth-observing satellites (Esa)

The European Space Agency is a space agency founded in 1975. It is responsible of space projets for 17 european countries.

Facilitate communication with the ground segment Envisat, archiving and distribution of the Envisat products under French responsibility.

RA-2 Geophysical Data Record product containing radar range and orbital altitude, wind speed, wave height, water vapour from the radiometer and geophysical corrections. Product delivers by Esa within 3 hours after the measurement.

Fasham Ducklow McKelvie Ecosystem model.

Level 2 data.

Available GDR data.

It's a is the scientific discipline  in the Earth sciences, that deals with the measurement and representation of the Earth, including its gravity field.

The shape of the sea surface assuming a complete absence of perturbing forces (tides, wind, currents, etc.). The geoid reflects the Earth's gravitational field (it is an equipotential surface) and varies in height by as much as 100 meters over distances of several thousand kilometers due to uneven mass distribution within the planet's crust, mantle and core. Other, less pronounced, irregularities are also visible over smaller distances. These reflect the ocean's bottom topography.

The radar pulse used to measure altimetry is subjected to a number of disturbances as it passes through the atmosphere and when it is reflected by the sea surface.

Altimetric satellite (US Navy).

Ocean circulation generated by the balance between the horizontal pressure gradient forces exerted by water masses and the effect of acceleration due to the Earth's rotation.

Global Energy and Water cycle Experiment (WCRP)

Altimetric Satellite (US Navy).

Germany's National Research Centre for Geosciences

The continents once covered by ice during last Ice Age are still reacting to the melting of this ice by going up (post glacial rebund).

Phase of the Geosat mission during which the satellite's orbit was designed to study the geoid.

One of three positioning systems on Topex/Poseidon that uses the GPS to determine the satellite's position.

See also: GPS, Doris, LRA, TRSR, Topex/Poseidon

A good proportion of the heat penetrating the Earth's atmosphere is not reflected back into space but is "trapped" by clouds and water vapor. This heat is thus returned to the surface, maintaining an average temperature of 15°C on Earth. Without it, the temperature would be nearer -18°C. Increasing quantities of certain gases in the atmosphere-called greenhouse gases-such as carbon dioxide are thought to amplify this phenomenon, leading to an increase in temperature on the surface of the globe.

The teams, hardware and software involved in controlling a satellite and in retrieving and processing its data.

Goddard Space Flight Center (Nasa).

Western boundary current of the subtropical gyre. The Gulf Stream is a strong current that transports warm waters from the Gulf of Mexico up the south coast of the United States to the Mid-Atlantic Ocean.

See Significant Wave Height (SWH).

Correction applied to allow for atmospheric forcing of the ocean surface. The sea level is lower when atmospheric pressure is high, and higher when atmospheric pressure is low.

French Ocean Agency

called now IPEV, Institut Paul-Emile Victor, french Institute for Polar Research and Technology

IGDR-M: IGDR Mixtes (Merged GDR);  IGDR-P: IGDR-Poseidon;  IGDR-T: IGDR-Topex

French National Geographical Institute

International GPS Service for Geodynamics.

IOD is known as atmosphere-ocean interaction phenomenon, with large impacts on surrounding areas.

Layer of the upper atmosphere where electron and ionization activity is particularly high.
Electromagnetic waves are subjected to a number of perturbing effects as they pass through the ionosphere.

The altimeter radar signal is delayed as it travels through the ionosphere. Free electrons slow the radar pulse, causing an error on altimetry measurements of the order of 0 to 30 centimeters. The value of this correction is determined by combining range measurements acquired at two different frequencies (Topex and Poseidon-2 altimeters), as it is inversely proportional to the square of the frequency. For mono-frequency altimeters such as that used on the ERS satellites, this value is determined using a statistical model of the ionosphere.

french Polar Institute

French Research Institute for Development (ex-ORSTOM).

JAMSTEC contributes to the advancement of academic research in addition to the improvement of marine science and technology by proceeding the fundamental research and development on marine,

Altimetric missions (Cnes/Nasa), follow-on of Topex/Poseidon. Jason-1 was launched on December 7, 2001 and Jason-2 was launched on June 20, 2008.

Jason-1 Microwave Radiometer.
See also : Satellite altimetry, Radiometer, Environment corrections, Jason-1, TMR

Scientific cruises around the Kerguelen Island (Indian Ocean) funded by the Agence Nationale de la Recherche (ANR), the Centre National de la Recherche Scientifique / Institut National des Sciences de l'Univers (CNRS / INSU) and the Institut Polaire Paul-Emile Victor (IPEV). 
Its purpose is to measure the biological activity depending on the chemical composition and the impact on the biogeochemical cycles.

Royal Meteorological Institute of Netherlands.

Western boundary current of the subtropical gyre. The Kuroshio Current is a strong current that transports warm waters from the China Sea and the Philippines up past Japan to the Mid-Pacific Ocean. It is the counterpart of the Gulf Stream in the North Atlantic.

See ENSO

Lamont-Doherty Earth Observatory.

Laboratoire des écoulements Géophysiques et Industriels.

The LEGOS (UMR 5566) is a joint research laboratory headed by : the Centre National d'Etudes Spatiales (CNES), the Centre National de la Recherche Scientifique (CNRS), the Institut of Recherchepour le Développement (IRD) and the Paul Sabatier University (UPS).

Its study fields are related to the environment focused on the physical ocean, marine geochemistry and biogeochemistry, spatial hydrology and dynamics of the polar ice caps, using remote sensing and five or observing networks.

Low Earth Orbit  

Line Feed

Length-Of-Day

Laboratoire d'Océanographie DYnamique et de Climatologie, called now, LOCEAN (Laboratoire d'Océanographie et du Climat : Expérimentation et Approches Numériques).

Laboratoire de Physique des Océans.

Dosimeter used to improve knowledge of particularly aggressive radiation. Passenger instrument onboard Jason-2 and Jason-3. Jaxa/Cnes contribution.

One of three positioning systems on Topex/Poseidon and Jason. The LRA uses a laser beam to determine the satellite's position by measuring the round-trip time between the satellite and Earth to calculate the range.

Large-Scale Geostrophic.

Maximum Cross Correlation.

the ocean topography due to the major currents.

Joint project to develop a high-resolution model of the global oceans, involving Cerfacs, Cnes, CNRS, Ifremer, Météo France, IRD and Shom.

French Meteorological Office

Mediterranean Forecasting System

Mediterranean Forecasting System Pilot Project

Miami Isopycnic-Coordinate Ocean Model.

Massachusetts Institute of Technology.

Mixed-layer

Multimission Modular Spacecraft.

Mercator North Atlantic prototype.

Muséum National d'Histoire Naturelle.

Modeling a phenomenon involves identifying its main characteristics and expressing them mathematically to better understand and, above all, predict how the phenomenon is likely to evolve.

Medium Orbit Ephemeris.

Modular Ocean Model.

Mouvements Océaniques et TEctoniques Verticaux par Altimétrie Spatiale.

Max-Planck Institute für Meteorologie.

The sea surface height averaged across all the oceans of the globe. An increase in the mean sea level is an indicator of a possible global warming.Mean Sea Level

Mean Sea Surface
Permanent component of the sea surface height. The mean sea surface comprises a geoid contribution (~100 m) and a permanent circulation contribution (~1 m).

Multi-Channel Singular Spectral Analysis.

Meridional Surface Wind Stress.

Multi-variate empirical orthogonal function.

Radial Speed measurer

MicroWave Radiometer (onboard ERS and Envisat).

MyOcean is a European project dedicated to operational oceanography. MyOcean Service provides the best set of information available on the Ocean for the large and regional scales (European seas), based on the combination of space and in situ observations, and their use into models: temperature, salinity, currents, ice extent, sea level, primary ecosystems...
The Sea Level observation data available within MyOcean are Ssalto/Duacs along-track data.

North Atlantic Oscillation.

The National Aeronautics and Space Administration (Nasa) is the space agency of the United States government, established in 1958.

North Atlantic

NAVal OCEANographic Office.

North Brazil Current

(Noaa)

(Noaa)

NERC is the UK's main agency for funding and managing research, training and knowledge exchange in the environmental sciences.

(Noaa)

(US)

See ENSO.

See ENSO.

National Meteorological Centre.

The National Oceanic and Atmospheric Administration (NOAA) is a scientific agency of the United States Department of Commerce focused on the studies of the oceans and the atmosphere.

Statistical quantity used to estimate the inherent error on measurements induced by the instrument itself.

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See also: Topex, Poseidon, Topex/Poseidon

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Data produced from the IGDR (i.e. using data computed with a preliminary orbit).

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Met Office's numerical weather prediction.

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The ocean and atmosphere are mutually interdependent. In particular, water that evaporates from the ocean causes the atmosphere to become hotter and more humid. This phenomenon affects atmospheric movements (winds), which in turn affect ocean circulation and so on: the temperature of air masses in contact with the ocean is modified and, conversely, ocean currents are driven by dominant winds. These ocean-atmosphere interactions are a major factor in weather forecasting and a key element in our understanding of climate.
Climate

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Technique used to grid data from along-track datasets

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 Variational data assimilation system based on the OPA Ocean General Circulation Model.

 The study of satellite orbits. Very precise determination of a satellite's exact position is a key factor in altimetry. On Topex/Poseidon and Jason, three orbit determination systems are used.

 Global configuration of the OPA model.

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 name of the Jason-2 satellite mission

 program to inform the general public about the projects. 

The Ovide project aims at documenting and understanding the variability of the circulation and water mass properties in the northern North Atlantic within the context of global change.

 Pacific Landfalling Jets Experiment.

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 Steady state of ocean currents in an idealized unchanging atmospheric system.

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 Person in charge of a research team working on a science project.

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The PISTACH project is funded by Cnes as part of OSTM/Jason-2 project to improve satellite radar altimetry product over coastal areas and continental waters.

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 Ocean, Altimetry and Climate Group.

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One of the two altimeters onboardTopex/Poseidon (Cnes); Poseidon-2 is the Jason-1 altimeter.
Poseidon-2

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 Minisatellite bus developed in France for Jason-1 and other missions.

Jason-1

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 Unit used to measure salinity in the ocean. One psu is one gram of salts per thousand grams of ocean, or about one gram per liter of water. Typical salinity in the ocean is 35 psu.

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 Passive instrument that detects and measures radiant energy, usually in the microwave, infrared and near-infrared wavebands.
Radiometers flown on altimetry satellites help us to measure water vapor and liquid water content in the atmosphere. These measurements are used to apply corrections to altimetry data. The radiometer's antenna collects radiation reflected by the ocean.
The amount measured depends on surface winds, ocean temperature, salinity, foam, absorption by water vapor and clouds, and other factors. To determine atmospheric water vapor content accurately, the surface and cloud contributions must be filtered out from the signal received by the radiometer. For this reason, different signal frequencies are used to increase sensitivity to each of these parameters. By combining measurements acquired at both frequencies, we can extract the water vapor signal.

 Arbitrary reference surface that is a raw approximation of the Earth's shape, which is basically a sphere "flattened" at its poles. The length of one of the axes at the Equator is chosen so that the ellipsoid coincides at this latitude with the mean sea level. For example, the ellipsoid used by the Topex/Poseidon mission has a radius of 6378.1363 km and a flattening of 1/298.257.

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Root Mean Square

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 The quantity of salts/salt content (sodium, potassium, silver salts, etc.) in sea water. Salinity plays an important role in the distribution and dynamics of water masses. In particular, it is a factor that affects downwelling of water to the ocean depths: highly saline water is more dense and therefore has a greater tendency to descend towards the ocean floor.

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Technique for measuring height. Satellite altimetry measures the time taken by a radar pulse to travel from the satellite antenna to the surface and back to the satellite receiver. Combined with precise satellite location data, altimetry measurements yield sea-surface heights.

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 Satellite for oceans observation(1978).

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 System of sequential assimilation modulus.

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 or sigma-naught
reflexivity coedfficient of the radar wave on the surface.

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Variations of the sea surface height with respect to a several-year mean or a mean sea surface. SLAs include seasonal variability.

The SLAs allow us to monitor ocean variability due to seasonal variations and climatic phenomena such as El Niño. Sea level variability (the standard deviation over time) is somewhere between 2-3 cm and 60 cm, depending on energy levels in different parts of the ocean.

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 Mean Sea Surface.

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 Model developed by Shom, the French Navy's hydrography and oceanography department, to forecast ocean circulation in the Northeast Atlantic.
See also:
-  Soprane

 also called NOCS, National Oceanography Center, Southampton.

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 Ocean Forecasting System on the Eastern-North Atlantic
Model used to forecast ocean currents and eddies. The successor to Soap.

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The Ssalto multimission ground segment (Segment Sol multimissions d'ALTimétrie, d'Orbitographie et de localisation précise) encompasses ground support facilities for controlling the Doris and Poseidon instruments, for processing data from Doris and the Topex/Poseidon, Jason-1 and Envisat-1 altimeters, and for providing user services and expert altimetry support.

 Bias due to the sea-surface state, which consists of two components: electromagnetic bias and tracker bias.

 Doris/Poseidon ground segment.

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Height of the sea surface with respect to a reference. In altimetry, usually, sea surface height with respect to the reference ellipsoid.

 see Sea Level Anomalies (SLA).

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 Water temperature at the ocean surface. The SST can be measured by satellite-based infrared radiometers.
See also:
-  Radiometer
-  AVHRR
-  ATSR

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Symbol H_s or H_1/3.
The significant wave height is obtained by analyzing the shape and intensity of the altimeter radar beam reflected from the sea surface (radar echo). A long time delay in the return signal indicates that waves are high and, conversely, a short delay indicates that the sea surface is calm.

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 Team working on the Topex/Poseidon and Jason-1 missions that meets at least once a year.

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 Terciles are range of values of a physical variables (e.g. precipitation, temperature...) defined so as to sort into 2 sections 1/3 of the lower, of the average and higher values of a distribution that could represent a climatology.

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 Zone between the colder water of the ocean depths and warmer surface water. Large temperature variations occur with depth in the thermocline zone. Near the surface, however, where water is always in motion, and in the ocean depths where there is no source of heat, the water temperature is fairly uniform.

 Large-scale global ocean circulation driven by variations in the temperature and salinity of water masses. Cooled and saline waters downwell at high latitudes (off the coast of Norway and Greenland). Waters warmed in the Tropics upwell to the surface, where they are cooled, and so on. It is estimated that a single water molecule takes about 1,000 years to complete the circuit.

Ocean tides can now be gauged to within 2 cm, thanks largely to altimetry. This has helped to improve our understanding of Earth-Moon interactions, such as the Moon's impact on the length of the day on Earth.

 Satellite (Nasa), that was launched with Jason-1.

  French educational program.

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 Radiometer onboard Topex/Poseidon.

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 Towards an operational prediction system for the North Atlantic and European coastal zones.

 One of the 2 altimeters (Nasa) onboardTopex/Poseidon.

 Altimetric satellite (Nasa/Cnes).

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 (ex UMR n°39).

 Timekeeping system that relies on atomic clocks to provide accurate measurements of the second, while remaining coordinated with the Earth's rotation, which is much more irregular. To stay synchronized, UTC has to be adjusted every so often by adding one second to the day, called a leap second, usually between June 30 and July 1, or between December 31 and January 1. This is achieved by counting 23h59'59", 23h59'60" then 00h00'00". This correction means that the Sun is always at its zenith at noon exactly (accurate to the second).

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The World Climate Research Programme, sponsored by the International Council for Science (ICSU), the World Meteorological Organization (WMO) and the Intergovernmental Oceanographic Commission (IOC) of Unesco, is uniquely positioned to draw on the totality of climate-related systems, facilities and intellectual capabilities of more than 185 countries. Integrating new observations, research facilities and scientific breakthroughs is essential to progress in the inherently global task of advancing understanding of the processes that determine our climate.

The two overarching objectives of the WCRP are:

1. to determine the predictability of climate; and
2. to determine the effect of human activities on climate.

 Water vapor in the atmosphere slows the radar pulse. This effect can generate mean errors of the order of 15 centimeters on altimetry measurements. The value of the correction applied is determined using measurements by radiometer on the satellite.

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The World Ocean Circulation Experiment (Woce) was a component of the World Climate Research Program and remains the most ambitious oceanographic experiment undertaken to-date.The aims of the programme were to establish the role of the oceans in the earth's climate and to obtain a baseline dataset against which future change could be assessed. Sophisticated numerical ocean models were also developed to provide a framework for the interpretation of the observations and for the prediction of the future ocean state.

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Project of altimeter-interferometer instrument; planned at first to be onboard Jason-2

or eXpendableBathyConductivity-Temperature-Depth.

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