Aquarius Level-3 Binning and Mapping

1. Aquarius Level-3 Binning and Mapping Fred Patt

2. Definitions • Projection - any process which transforms a spatially organized data set from one coordinate system to another. • Mapping - a process of transforming a data set from an arbitrary spatial organization to a uniform (rectangular, row-by-column) organization, by processes of projection and resampling. • Binning - a process of projecting and aggregating data from an arbitrary spatial and temporal organization, to a uniform spatial scale over a defined time range. Ideally the binning process will preserve both the central tendency (e.g., average) and the variation in the data points that contribute to a bin.

3. NASA Ocean Product Projections • Equal-area: sinusoidal, with equally space rows and number of bins per row proportional to sine of latitude. • Equal-angle: rectangular (Plate Carrée) with rows and columns equally spaced in latitude and longitude. • Ocean equal-area and equal-angle projections are equivalent at the equator.

4. Sinusoidal Equal-Area Projection

5. Why Use Equal-Area Bins? • When generating large-area (global or regional) averages, equal-area bins provide correct areal weighting without correction. • Other uses (e.g., models) may also require equal-area inputs. • Ultimately the decision about a binning projection is driven by science needs.

6. Binned and Mapped Products • Binned products are generated daily from Level-2, and then aggregated to weekly, monthly, seasonal, annual and mission. • Standard mapped image (SMI) products are generated at each temporal resolution by projecting binned files to the equal-angle grid.

7. Binned Product Format • Metadata indicates product type, start/end dates, and geographic extent. • Bin geometry parameters describe projection and resolution. • Binned data are stored in record format: • Common fields for all parameters (e.g, number of observations, temporal information, weighting). • For each parameter, central tendency (e.g., average) and variability (e.g., std dev). • Only bins with observations are stored.

8. Mapped Product Format • One product for each geophysical parameter • Metadata similar to binned product. • Map parameters describe projection and resolution. • Mapped data are stored in array format: • Current Ocean mapped products use scaled integers for data. • Fill values for unfilled points

9. Questions • What is the optimum method for averaging? • What information should be saved about the variability? • Will additional post-processing (i.e., smoothing) be required? • How can testing with various kinds of noise be incorporated into the mission simulation? • Should temporal sampling information (e.g., days of the month that contributed to a data point) be preserved? • How should the beam footprint-to-bin registration be handled?