The Goddard Earth Sciences Data and Information Service Center (GES DISC) has now made available selected global daily and monthly Sea-viewing Wide Field-of-view Sensor (SeaWiFS) aerosol data parameters in the new Giovanni Version 4 (G4) system (http://giovanni.gsfc.nasa.gov/giovanni/).
SeaWiFS aerosol data products are provided by Dr. Christina Hsu’s research group through the "Consistent Long-Term Aerosol Data Records over Land and Ocean from SeaWIFS" project, which is part of the NASA Making Earth Science Data Records for Use in Research Environments (MEaSUREs) Program. The SeaWiFS aerosol data cover the period from September 4, 1997 to December 11, 2010. Documentation and other data services can be found at the MEaSUREs/SWDB online portal.
Improvements and new features in G4 include the following:
a. A single interface, an “omnibus portal,” which makes it easy to find data parameters in the Giovanni database, especially if the same parameters are available from different sensors. This portal enables intercomparison of similar variables derived from different sensors or examination of relationships between any two variables.
b. Much improved system performance when plotting extended time-series. For example, the new Giovanni is about four times faster in generating a three-year-long time-series plot of daily global averaged aerosol optical thickness (AOT) at 550 nm at 1° x 1° resolution (~2 min with G4 and ~9 min with the predecessor Giovanni-3 system).
c. New visualization functions, e.g., Interactive Map and Time-Averaged Scatter Plot (interactive scatter plot), area-averaged scatter plot, and seasonal or monthly time-series. The interactive map supports both zooming and panning. It is now also possible to download a data animation as a GIF file.
d. Error reports or comments can be submitted by simply clicking on the “Feedback” button.
All SeaWiFS daily and monthly aerosol variables at 0.5° and 1.0° resolution in Giovanni-3 have been incorporated into the new G4 database, but only the following three most popular variables are currently available to the public:
Other variables will be made available by request in the future.
Visualization of monthly climatology and data anomalies will be added into the system later in the development process. Monthly climatology aerosols were pre-calculated by averaging the monthly data through the entire mission. (The monthly anomaly is the difference in data value for a specific month from the climatological average for that month.) Most G4 visualization functions can be applied to the monthly climatology and anomaly data.
The following is an example of the steps required to make a “time averaged scatter plot” for monthly aerosols at 550 nm from SeaWiFS and MODIS-Terra, over southwestern Asia in spring (Mar-Apr-May) 2005:
- Select plot: From the pull-down menu, “Comparison → Time-Averaged Scatter”
- Select Date Range: Start Date: 2005-03-01, End Date: 2005-05-31
- Select Region: (58, 6, 95, 36), (i.e., 58E-95E, 6N-36N)
- Select Variables:
- Use the keyword “SeaWiFS” and click on Search, which will list all available variables from SeaWIFS. Currently, a total of 12 parameters will be listed.
- Refine the list through the faceted navigation on the left panel by selecting “Monthly” from “Temporal Resolutions.”
- Select the variable “Aerosol Optical Depth 550 nm (SWDB_L3M10 v004) at 1.0 deg resolution.”
- Use the keyword “MODIS-Terra monthly” to list all monthly data parameters from MODIS-Terra monthly.
- Select the variable “Aerosol Optical Depth 550 nm (Dark Target) (MOD08_M3 v051) at 1.0 deg resolution.”
- Click “Plot Data” to generate the scatter plot, which should appear similar to Figure 1. On the resulting plot page, the right panel shows the plot history, including User Input, Plots, Plot Options, Downloads, and Lineage. The URL for this plot can be saved and shared with other users, as described in the caption.
Figure 1: Example of the G4 time-averaged scatter plot function. (Click on the image to view it full-size.) Clicking the URL below for will allow examination of the same plot with the interactive scatter plot function in G4. When the G4 interface has loaded, click the Plot Data button (bottom right) to view the plot.
The result is an interactive scatter plot that allows a user to examine the data quickly and potentially determine the location of outliers or unusual data points. Data points can be selected on the scatter plot and their locations viewed on the map, or a region may be selected on the map to immediately allow a view of the corresponding scatter plot.