What Are We Seeing in Aquarius Data?
Aquarius data have revealed interesting features in the global ocean, including a salty patch of water in the North Atlantic Ocean. Evaporation of water from this area leaves behind large amounts of salt, contributing to a high-salinity region.

Near the equator in the North Pacific Ocean, one of the wettest regions on the planet, heavy rainfall adds an abundance of water to the sea surface. This results in a band of low salinity water off the coast of Central America.

Rivers also influence the amount of salt on the sea surface. At the mouth of the Amazon River, millions of gallons of freshwater flow into the Atlantic Ocean, resulting in a plume of low-salinity water.

At high latitudes, the seasonal melting of sea ice causes a sharp decrease in sea surface salinity. In spring and summer, surface currents in the Labrador Sea transport low salinity water south, where it meets warmer, saltier water carried north by the Gulf Stream.

The waters surrounding the Indian subcontinent vary in salinity due to geography and climate. To the west, an arid climate and lack of freshwater input yields the salty Arabian Sea. To the east, monsoon rains and freshwater outflow from the Ganges River keep the Bay of Bengal far less salty.

Without satellite observations, these global changes would be largely invisible to us. Aquarius data are helping scientists to better understand our vast ocean, including how changes in ocean circulation and the water cycle may impact Earth's climate.
Salt. Most people view it first and foremost as the most common condiment. It comes in many forms and has thousands of uses, from preserving food to manufacturing pharmaceuticals. But salt also plays an important role in how the Earth system functions. And just as salt flows through our veins, it also flows through Earth's ocean, the lifeblood of Earth's climate system. The ocean is roughly 3.5% salt and the concentration of dissolved salts in the ocean is referred to as salinity, which varies across the globe and over time.

Just as too much or too little salt in our diets affects our health, so too do high and low salinity have profound effects on how the ocean circulates, how freshwater cycles around Earth and how our climate works. The concentration of salt on the ocean surface — the part of the ocean that actively exchanges water and heat with Earth's atmosphere — is a critical driver of ocean processes and climate variability.

To better understand the regional and global processes that link variations in ocean salinity to changes in the global water cycle - and how these variations influence ocean circulation and climate - NASA built and launched Aquarius, the primary instrument aboard the international Aquarius/Satélite de Aplicaciones Científicas (SAC)-D observatory.

Aquarius made NASA's first space-based global observations of ocean surface salinity, flying 657 kilometers (408 miles) above Earth in a sun-synchronous polar orbit that repeated every seven days. This NASA Earth System Science Pathfinder mission mapped global changes in ocean surface salinity with a resolution of 150 kilometers (93 miles), showing how salinity changes from month to month, season to season and year to year. Scientists are combining Aquarius data with in-water measurements to generate operational maps of ocean salinity distribution.

The Aquarius/SAC-D mission was developed collaboratively between NASA and Argentina's space agency, Comisión Nacional de Actividades Espaciales (CONAE) to best meet the goals of each agency while giving priority to salinity measurements. CONAE built complementary sensors to detect rain, sea ice, and wind speed, plus sea surface temperature sampling. CONAE-sponsored instruments — including sensors from the French Space Agency (Centre National d'Etudes Spatiales, CNES) and another from the Italian Space Agency (Agenzia Spaziale Italiana, ASI) — provide environmental data for a wide range of applications, including natural hazards, land processes, epidemiological studies, and air quality issues.

Key Facts About Sea Surface Salinity
and the Aquarius Instrument
Absolute salinity is defined as the concentration of dissolved salts in seawater, historically expressed in grams per kilogram, or parts per thousand.

Aquarius created a new map of global ocean surface salinity every seven days.

Modern oceanography uses the Practical Salinity Scale (PSS) to derive salinity from precise instrument measurements of seawater electrical conductivity, temperature and pressure (depth).

The ocean average of sea surface salinity is about 35 PSS (or about 3.5% salt). Over the globe, sea surface salinity ranges from 32 to 37 PSS.

The goal of Aquarius was to measure salinity changes of 0.2 PSS, equivalent to about 2 parts in 10,000, every month.

The Aquarius sensor detected subtle changes in the ocean's microwave emission that are caused by salinity.

The radiometers developed for Aquarius were the most accurate ever developed for Earth remote sensing at the frequency of 1.4 GHz.

Aquarius's three radiometers were aligned with a 2.5 meter (8.2-foot)-diameter antenna reflector to generate three beams whose "footprints" created a 390-kilometer (242-mile)-wide swath on the ocean surface.

Salinity variations are driven by precipitation, evaporation, runoff, and ice freezing and melting.

Like vegetation patterns on land, global salinity patterns are linked to rainfall and evaporation.

Seawater density is governed by temperature and salinity.

Below the wind-driven surface - tens to hundreds of meters - ocean circulation is driven by changes in seawater density.

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