ECCO: Integrating Ocean & Ice

ECCO: Integrating Ocean & Ice You'll find a wealth of information in ECCO Version 4 Release 4

ECCO strives to incorporate all possible observations of the ocean and sea ice into its ocean circulation model. What kinds of data are used in the latest ECCO state estimates?

Our ocean is in constant motion and measuring sea surface height is challenging. However, radar altimeters are up to the task. These devices sends pulses, which bounce off the ocean surface and return to the satellite. The round-trip time is related to the distance above the ocean. From hundreds of miles above Earth, radar altimeters can measure sea surface height within 2-3 cm (1 in)!

Sea surface height data come from radar altimeters on satellites such as...

TOPEX/Poseidon

TOPEX/Poseidon was a joint satellite mission between NASA and the French Space Agency (Centre National d'Études Spatiales, CNES). It was launched from Kourou, French Guiana on August 10, 1992. This satellite corrected for factors that affect radar's travel time such as water vapor in the atmosphere. What about waves? Each signal was taken over a 10-km (6-mi) area to average them out. Ground-based equipment –including lasers – and GPS trackers helped pinpoint its orbital position. (Photo: Arianespace)

NASA Jet Propulsion Laboratory (JPL): 25 Years of Global Sea Level Data, and Counting

Jason Series

Jason-3 in a "clean room" prior to launch. It is the third in a series of ocean altimeters that were launched by international teams including NASA and CNES. Together with TOPEX/Poseidon, the Jason series of radar altimeters has measured sea surface height – and global sea level rise – for nearly three decades. This long-term record enables scientists to accurately understand climate change in our ocean.

NASA: Ocean Surface Topography from Space

ECCO Timeline

SARAL/AltiKa

Launched on 25-Feb-13, SARAL/AltiKa is a satellite developed and built by the Indian space agency (ISRO). AltiKa is a Ka-band altimeter built by CNES and operates onboard SARAL. Previous altimetric missions have been Ku or C-band. However, Ka-band provides better resolution for coastal areas, and is nearly insensitive to path delays in Earth's ionosphere.

CNES: Saral/AltiKa

Sea surface height anomaly data show differences from normal conditions. El Niño is characterized by unusually warm ocean temperatures in the eastern equatorial Pacific. In this case, the sea surface is higher than normal as shown in red. Why is it higher? Warm water associated with El Niño displaces colder water in the upper layer of the ocean. Thermal expansion of the warm water causes an increase in sea surface height.

NASA Physical Oceanography Active Archive Center (PODAAC): Sea Surface Height

Mean dynamic topography (MDT) is the long-term average of the difference between the mean sea surface and Earth's geoid. MDT contains information about the speed and direction of the ocean's mean surface currents. These currents move along constant values of MDT (i.e., topographic contours). The steeper the slope, the faster the current. Flow direction depends on the hemisphere in which they are located (e.g., clockwise motion around "hills" in the northern hemisphere). MDT products combine information from various satellite instruments and in-water instruments.

A New Ocean Mean Dynamic Topography Model, Derived from a Combination of Gravity, Altimetry and Drifter Velocity Data (Knudsen, Andersen, and Maximenko, 2020)

The geodetic MDT model DTU17 with units of dynamical meters. Variations in MDT are mainly caused by ocean temperatures and permanent ocean currents like the Gulf Stream and the Kuroshio.

Temperature and salinity (i.e., the concentration of dissolved salt) are two of the most commonly measured properties of our ocean. Why? Below the wind-blown ocean surface, temperature and salinity help drive ocean currents around the globe. These currents transport heat and marine life, including tiny algae that convert carbon dioxide to oxygen. Thus, understanding the motion of our ocean is important to "getting to the bottom" of changes in climate.

Data come from a variety of in-water instruments such as...

Argo Profiling Floats

Argo is a global array of thousands of free-drifting profiling floats that measures the temperature and salinity of the upper 2000 m (about 6500 ft) of the ocean. This allows 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.

Scripps Institution of Oceanography: Argo

Conductivity, Temperature and Depth (CTD) Sensors

A CTD measures temperature and salinity as a function of depth as the instrument is lowered through the water column. In this photo, the CTD is located at the bottom of the instrument package, oriented horizontally. The gray cylinders are Niskin bottles, used to collect seawater at various depths.

National Oceanic and Atmospheric Administration (NOAA): What does “CTD” stand for?

Instrumented Marine Mammals

Some marine mammals travel thousands of kilometers to find their food, continuously diving to great depths. By instrumenting them, it is possible to directly observe their foraging behavior and collect oceanographic data in remote regions. The Marine Mammals Exploring the Oceans Pole to Pole (MEOP) consortium brings together several national programs to produce a comprehensive quality-controlled database of oceanographic data using instrumented marine mammals. World map shows the tracks of instrumented mammals from an international consortium of investigators.

Marine Mammals Exploring the Oceans Pole to Pole (MEOP)

Autonomous Underwater Gliders

Example in-water temperature data taken by an autonomous glider during February 2012. Red colors indicate warmer water near the sea surface. Blue colors indicate cooler water at depth.

In-water salinity data taken at the same time as the temperature data shown above. Yellow and orange colors indicate higher salinity water near the sea bottom. Blue colors indicate fresher water through most of the water column. (Data from the North Carolina Coastal Ocean Observing System)

NOAA: What is an Ocean Gilder?

Ice-Tethered Profilers (ITP)

The ITP was designed to repeatedly sample the properties of the ice-covered Arctic Ocean at high vertical resolution. The system consists of a small surface capsule that sits atop an ice floe and supports a plastic-jacketed wire rope tether that extends through the ice and down into the ocean, ending with a weight (intended to keep the wire vertical). A cylindrical underwater instrument (in shape and size much like an Argo float) mounts on this tether and cycles vertically along it, carrying oceanographic sensors through the water column. Water property data are telemetered from the ITP to shore in near-real time. (Photo: Chris Linder, Woods Hole Oceanographic Institution, WHOI)

WHOI: Ice-Tethered Profilers

Moorings

Tropical Atmosphere Ocean (TAO) is a moored buoy array located across the equatorial Pacific Ocean. Its surface and sub-surface observations are critical for understanding the El Niño Southern Oscillation. (Photo: Lieutenant Elizabeth Crapo, NOAA Corps)

NOAA: Global Tropical Moored Buoy Array

Expendable BathyThermographs (XBTs)

These in-water instruments retrieve ocean temperature but not salinity.

An XBT is a small probe that is released from the side of a ship. As it falls through the water, it measures temperature. Small wires transmit the temperature data back to the ship where it is recorded for further analysis. Because the probe falls through the water at a known rate, the depth of the probe can be inferred from the time of launch. The deployment of an XBT does not require the ship to slow down or otherwise interfere with normal operations, so XBTs are often deployed from vessels of opportunity, such as cargo ships or ferries, rather than a dedicated research ship where a CTD would normally be used.

More Than 50 Years of Successful Continuous Temperature Section Measurements by the Global Expendable Bathythermograph Network, Its Integrability, Societal Benefits, and Future (Goni et al., 2019)

ECCO also constrains its model using data from sensors on satellites such as...

Advanced Very High Resolution Radiometer (AVHRR)

AVHRR is a broad-band multiple-channel scanner, sensing in the visible, near-infrared, and thermal infrared portions of the electromagnetic spectrum. It is used to monitor sea surface temperature over the globe. AVHRR instruments are or have been carried by the NOAA family of polar orbiting platforms and European MetOp satellites.

NOAA: Optimum Interpolation Sea Surface Temperature

NASA Aquarius

The Aquarius/SAC-D mission was a joint venture between NASA and Argentina's space agency, Comisión Nacional de Actividades Espaciales (CONAE). Data collected by NASA's Aquarius instrument were used with sea surface temperature collected from other satellites. Sea surface salinity data from Aquarius played a large role in understanding both oceanography and the global water cycle.

PODAAC: Salinity Data

Animation of global sea surface temperature over from September 1981 to July 2019. Warmer ocean temperatures are shown as red and orange. Blues indicate colder waters, generally near the poles. Data are from the Group for High Resolution Sea Surface Temperature (GHRSST) global sea surface temperature analysis produced daily on a 0.25 degree grid at the NOAA National Centers for Environmental Information.

This video provides a global tour of sea surface salinity using measurements taken by NASA's Aquarius instrument aboard the Aquarius/SAC-D spacecraft, from December 2011 through December 2012. Red represents areas of high salinity, while blue represents areas of low salinity. Aquarius was NASA's first effort to measure sea surface salinity from space, providing the global view of salinity variability needed for climate studies.

Another data source for ECCO are long-term averaged fields of ocean temperature and salinity, known as "climatology" data. These data grids are provided by the NOAA World Ocean Atlas at 1-degree spatial resolution. The fields are three-dimensional: interpolated onto vertical intervals from the surface (0 m) down to great depth (5500 m or 16,400 ft). Averaged fields are produced for annual, seasonal and monthly time-scales.

Annual mean conditions at the sea surface. Temperature is shown at left with red colors indicating warm water and purples indicating cold water Salinity is shown at right with saltier waters shown in red and fresher waters in blue. (Source: World Ocean Atlas, 2009)

NOAA National Centers for Environmental Information: World Ocean Atlas 2009

In addition to sea surface height, ocean temperature and salinity data, ECCO includes...

Sea Ice Concentration

Sea ice concentration data have been acquired by the Special Sensor Microwave/Imager (SSM/I) and the Special Sensor Microwave Imager/Sounder (SSMIS). These passive microwave sensors offer an extensive data record which spans from 1978 through the present.

National Snow & Ice Data Center (NSIDC): SSM/I-SSMIS Overview

NSIDC: Arctic Sea Ice News & Analysis

Ocean Bottom Pressure

Ocean bottom pressure is the sum of the mass of the atmosphere and ocean in a "cylinder" above the seafloor. This visualization shows monthly changes in ocean bottom pressure data obtained by the twin Gravity Recovery and Climate Experiment (GRACE) satellites from November 2002 to January 2012. Purple and blue shades indicate regions with relatively low ocean bottom pressure, while red and white shades indicate regions with relatively high ocean bottom pressure. Scientists use these data to observe and monitor changes in deep ocean currents, which transport water and energy around the globe.

NASA JPL: GRACE-FO Mission

ECCO makes optimal use of these valuable and diverse data streams.

How? By fitting ocean models to all of these observations while obeying the laws of physics.

Learn more at ecco-group.org

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