Date: 19 February 2009
The Aquarius 28-day preliminary simulated data set is provided to give prospective users of Aquarius ocean salinity data a preview to the Level 2 science data in order to become familiar with the global sampling pattern. An Aquarius/SAC-D mission description is given by Lagerloef, et al (2008) (http://www.tos.org/oceanography/issues/issue_archive/issue_pdfs/21_1/21.1_lagerloef.pdf). The Aquarius/SAC-D mission will fly in a sun-synchronous polar orbit with an ascending equatorial crossing time of 6pm (local) and a nominal equatorial altitude of 657 km. The orbit has an exact repeat cycle in 7-days (103 revolutions). The cross track spacing at the equator, as well as the 3-beam swath width, are 390 km, ensuring complete global coverage.
ECCO JPL ocean model global SSS and SST fields are used for the target month of this simulation; November 2004. NCEP fields for the same period are used for winds and other atmospheric variables. Other external constraints include solar radiation assumed to be the peak of the previous solar max, peak ionosphere total electron count. A simulated orbit ephemeris was then used to sample the fields along the satellite trajectory over one complete 7-day cycle at a sample rate of 1.44 seconds. A radiative transfer model was then used to compute the antenna brightness temperatures at V-pol, H-pol and 3rd Stokes parameter at the L-band frequency 1.413 GHz.
A preliminary Level 2 science data file specification document is available at http://oceancolor.gsfc.nasa.gov/AQUARIUS/DOCS/Aquarius_Level-2_Data_Product.doc. This guide describes the file name conventions and the descriptions of variables in the HDF5 formatted files. The variable list in this document is not yet complete and more parameters are to be added. Furthermore, only a very small subset is included in these preliminary test data files. They include simulated radiometer brightness temperatures, salinities and navigation data for each beam, primarily to give users in introduction to the sampling pattern and range of antenna brightness temperatures and SSS. Simulated radar data are not included at this time, nor are the data flags. The final L2 science data file will be much more comprehensive. Each file covers one orbit revolution, starting from south to north and back to south, plus an overlap (~10 minutes??) from one orbit file to the next to ensure that a seamless transition is recovered when the data are concatenated by the user. (The overlap portions should be exact duplicates.) Accordingly, there are 103 files for each 7-day repeat cycle, and a total of 412 files for this entire 28-day simulation.
The Level-3A files represent all the simulated Sea Surface Salinity observations made during a 28 day period mapped to an equirectangular projection having one degree resolution.
Aquarius has three radiometers and feed horns and the files in this directory represent the values observed by each feed horn individually (B1, B2 and B3) and also one in which all three feed horns have been averaged together.
The Level-3B file represents the "smoothed" global" product as described in the theoretical basis document found at: http://oceancolor.gsfc.nasa.gov/AQUARIUS/DOCS/Aquarius-gridding-implementation.feb2009.pdf
Questions about these preview data sets can be directed to the following people.