Glossary of Terms

Altimetry: Altimetry is the measurement of height. Jason-3 measures sea surface height from space.

AMR-2: The Advanced Microwave Radiometer-2 is an instrument onboard the Jason-3 satellite that measures water vapor content in the atmosphere in order to calculate the travel time delay of the radar signal from the Poseidon-3B Altimeter down to Earth and back to the spacecraft.

Bathymetry: Measurement of the depth of the ocean. Satellite radar altimeter measurements of the ocean surface height can be used to infer the presence of mountains below the ocean surface. Mountains on the seafloor add extra pull to Earth's gravity field, drawing more water around them and bulging the sea surface outward. This way of estimating depth is called "altimetric bathymetry".

Data: Numerical or other information represented in a form suitable for processing by computer.

ENSO: ENSO stands for El Niño/Southern Oscillation. The ENSO cycle refers to the year-to-year variations in sea surface temperatures, convective rainfall, surface air pressure, and atmospheric circulation that occur across the equatorial Pacific Ocean. El Niño and La Niña represent opposite extremes in the ENSO cycle.

DORIS: The Doppler Orbitography and Radio-positioning Integrated by Satellite instrument onboard Jason-3 provides precise orbit determination and locates the satellite on orbit in real time.

GPSP: The Global Positioning System Payload is a Global Positioning System receiver that will determine the satellite’s position using signals received from the Global Navigation Satellite System.

Jason-2: A joint, international effort by four organizations--NOAA, NASA, EUMETSAT and CNES--to measure sea surface height by using a radar altimeter mounted on low-earth orbiting satellites. This is also referred as Ocean Surface Topography Mission (OSTM).

LRA: The Laser Retro-reflector Array is an instrument on Jason-3 that allows the satellite to be tracked with centimeter accuracy by 40 ground-based, satellite laser ranging stations.

Mission: The full life cycle development and operation of a particular satellite.

Ocean Heat Content: The heat stored in the ocean. Ocean Heat Content analysis from NOAA uses data from ships and buoys to estimate the total amount of heat energy contained in the ocean from 0 to 700 meters in depth. Changes in ocean heat content plays a role in sea level rise because of thermal expansion.

Ocean Surface Topography Mission: A joint, international effort by four organizations--NOAA, NASA, EUMETSAT and CNES--to measure sea surface height by using a radar altimeter mounted on low-earth orbiting satellites.

Ocean Surface Winds: A crucial measurement for ships, satellite-based sensors operating at microwave frequencies can measure the ocean surface day and night and under nearly all-weather conditions. Both active (radar) and passive (radiometer) microwave sensors have been shown capable of retrieving the ocean surface wind speed, with active microwave instruments being used to also retrieve the wind direction.

Payload: An instrument or communications component mounted on the spacecraft that provides data or communications service to fulfill mission goals.

Poseidon-3B Altimeter: The primary instrument on Jason-3, Poseidon-3B is a radar altimeter that maps sea surface topography used to calculate ocean surface current velocity, wave height, and wind speed.

Precision Orbit Determination: A method used to determine the exact position of a satellite in orbit. Typically, the orbit is calculated on the ground and this information is combined with the other instrument data to make final products like altimetry measurements.

Product: Derived data from the raw instrument measurements in a specific output format.

Satellite: The orbital system comprising the spacecraft bus, instruments, and any other payloads.

Satellite Radar Altimetry: Satellite radar altimetry is a method to measure the ocean surface height (sea level) by measuring the time it takes a radar pulse to make a round-trip from the satellite to the sea surface and back. This requires knowing the satellite’s precise position in orbit.

Sea Level: Generally refers to the mean sea level (MSL), or the average level of the surface of Earth’s oceans. Global changes in MSL, either a sea level rise or sea level fall, have been recorded using satellite altimetry data since 1992.

Sea Level Rise: One of the most significant potential impacts of climate change, sea level rise may cause flooding of coastal areas and islands, shoreline erosion, and destruction of important ecosystems such as wetlands and mangroves.

Sea Surface Height: The ocean surface ripples and undulates due to wind and waves, rises with the tidal pull of the moon, expands and contracts as it heats and cools, and billows due to circulation patterns. Sea surface height anomaly data is able to characterize these small- and large-scale changes over weeks and years. Since 1992, the Ocean Surface Topography Mission has been taking detailed satellite measurements of the ocean surface for weather, climate and undersea mapping applications.

Spacecraft Bus: The spacecraft bus consists of the necessary hardware and software required to accommodate the instruments and auxiliary communication services payloads.

TOPEX/Poseidon: Launched in 1992, TOPEX/Poseidon was a joint satellite mission between NASA and CNES (the French space agency) to map ocean surface topography.

Topography: The measure of the surface of something. Ocean surface topography is mapped using sea surface height measurements relative to Earth’s geoid, or a representation of the shape the ocean surface would be if the ocean were stationary.