Spacecraft and Instruments

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Aquarius will measure sea surface salinity by observing the natural thermal emission from the ocean surface with an instrument called a radiometer. At frequencies near those used in microwave ovens, the level of emitted signal depends on the salinity of the ocean water, in addition to temperature. This energy, which is measured as an equivalent “brightness” temperature in Kelvin, has a direct correlation to surface salinity. Other things being equal, salty water appears cooler than freshwater.

Over the open ocean, salinity ranges only from about 32 to 37 PSS. An accuracy of about 0.2 PSS is needed to achieve the mission’s science goals. This corresponds to a change in brightness temperature of about 0.1 Kelvin which is a challenging measurement for an Earth remote sensing instrument.

In addition, Aquarius must correct for interference with the salinity signal from other sources. Ocean waves are a particular problem because they modify the emission and can confuse the signal from salinity. Thus Aquariushas an additional instrument onboard, a radar scatterometer, to measure and correct for the effects caused by ocean waves.

Complementing data from Aquarius, the SAC-D payload has CONAE-sponsored instruments, including sensors from the French Space Agency (Centre National d’Etudes Spatiales) and the Italian Space Agency (Agenzia Spaziale Italiana) (see table above).

Once the satellite is on orbit, mission operations will be conducted at the CONAE ground station in Córdoba, Argentina. CONAE will transmit raw Aquarius data to the ground system at NASA’s Goddard Space Flight Center (GSFC) in Greenbelt, Md., where the data will be processed and instrument operations managed. The Aquarius data processing system will generate timely salinity products to be disseminated by and archived at NASA’s Physical Oceanography Distributed Active Archive Center (PO.DAAC) at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

Aquarius/SAC-D Science Instruments
Instrument Objective Description Resolution Source
Aquarius Sea surface salinity • Integrated 1.413 GHZ polarimetric radiometer
• 1.26 GHz radar
• 390 km swath
3 beams
• 76 x 94 km
• 84 x 120 km
• 96 x 156 km
Microwave Radometer
Precipitation, wind speed,
sea ice concentration, water vapor
• 23.8 GHz and 36.5 GHz
• Dual polarized
• 390 km swath
• 40 km CONAE
New Infrared Sensor
Hot spots (fires), sea surface temperature • Bands: 3.8, 10.7, and 11.7 μm
• Swath: 180 km
• 350 m CONAE
High Sensitivity Camera
Urban lights, fires, aurora • Bands: 450 - 900 μm
• Swath: 700 km
• 200 - 300 m CONAE
Data Collection System
Environmental data collection • Band: 401.55 MHz uplink • 2 contacts per day
with 200 platforms
Radio Occultation Sounder for Atmosphere
Atmosphere temperature and humidity profiles • GPS occulation • Horizontal: 300 km
• Vertical: 300 km
ASI (Italy)
ICARE: Effect of cosmic radiation on electronics
SODAD: Distribution of microparticles and space debris
• ICARE: Three depleted Si and Si/Li detectors
• SODAD: Four SMOS sensors
• ICARE: 256 channels
• SODAD: 0.5 μ at
20 km/s sensitivity
CNES (France)