Gayana 68(2) supl. t.I. Proc. : 121-122, 2004 ISSN 0717-652X

THE SAC-D/AQUARIUS MISSION, SCIENTIFIC OBJECTIVES

F. Raul Colomb¹, Gary S.E. Lagerloef², David Le Vine³, Ida Nollmann⁴ & Yi Chao⁵

1. Comisión Nacional de Actividades Espaciales (CONAE), Buenos Aires, AR, rcolomb@conae.gov.ar
2. Earth and Space Research, 1910 Fairview Ave E, Suite 210, Seattle WA 98102-3620 lager@esr.org
3. NASA/Goddard Space Flight Center, Greenbelt, MD USA David.M.LeVine@nasa.gov
4. Comisión Nacional de Actividades Espaciales (CONAE), Buenos Aires, AR, nollmann@conae.gov.ar
5. NASA Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, Yi.Chao@jpl.nasa.gov

SAC-D/Aquarius is a multi-sensor mission covering ocean, land, atmosphere and space environments, being developed by Argentina and the United States with additional payload contributions from Italy and France (Table 1). Launch is planned for September 2008, to a sun-synchronous 6pm ascending orbit at 657 km altitude. The primary science goal is to study the processes that couple changes in the water cycle and ocean circulation, and influence present and future climate, by measuring sea surface salinity (SSS) variations globally for at least three years. Additional objectives include

· Monitoring environmental changes, natural hazards and sea ice.

· Monitoring atmospheric parameters.

· Studying effect of cosmic radiation on electronic devices and characteristics of space debris.

The NASA Aquarius L-band microwave sensor is the first of its kind to be developed specifically for accurate SSS measurements. This instrument is a 1.413 GHz polarimetric microwave radiometer, with an integrated 1.26 GHz scatterometer to derive a sea-state roughness correction. Aquarius has a fixed 3-beam configuration with ~320 km wide swath that will provide global ocean coverage every 7 days with ~100 km spatial resolution. The data will gridded into monthly analyses with 0.2 psu accuracy. The key Aquarius science objectives are 1) to improve closure of the mean and seasonal global ocean-atmosphere freshwater balance, 2) to study the influence of SSS variability on tropical dynamics and ENSO, and 3) to analyze large scale SSS changes in mid to high latitudes that influence mode water formation, ocean convective overturning circulation and long term climate variability. The Aquarius data can also be used to derive coarse resolution soil moisture content over land.

CONAE is developing a Ka-band microwave Radiometer (MWR) for SAC-D/Aquarius to provide measurements of surface wind, rain, cloud liquid water and water vapor and sea ice over the ocean, and possible snow cover parameters on land. The MWR includes polarimetric measurements at 23.7 GHz and 37 GHz with an 8-beam push broom configuration with ~40 km resolution. The MWR and Aquarius swaths overlap to provide ancillary wind and rain information to improve the Aquarius SSS measurement retrievals.

CONAE optical instruments include 1) the New Infra Red Scanner Technology (NIRST) and 2) the High Sensitivity Camera (HSC). NIRST is designed primarily for measuring high temperature thermal events (biomass fires, volcanic events, etc.) and their thermal energy release, as well as limited sea surface temperature data. NIRST carries 4, 11 and 12µ IR channels with 150 m resolution and 75 km swath that can be pointed ±350 km either side of the ground track. The HSC is a 450-900 nm panchromatic camera to detect electric storms, urban lighting, fires and aurora events at night over a ±700 km swath and 200 - 300 m pixel resolution. A Data Collection System (DCS) to telemeter environmental data from automated ground stations, and a spacecraft engineering technology demonstration package, complete the set of Argentine instruments designed and built by CONAE.

The ROSA instrument, from the Italian Space Agency (ASI), will apply GPS occultation techniques to profile the atmosphere (temperature and humidity) and ionosphere (electron density). The ICARE/SODAD instrument, from the French Centre National d'Etudes Spatiales (CNES), will make in situ measurements of cosmic radiation effects (ICARE) and orbiting micro particles and space debris (SODAD).

Figure 1: SAC-D/Aquarius.