General Description of Giovanni
Giovanni provides a World Wide Web (WWW) interface that enables access to global data sets from NASA Earth remote-sensing missions and other environmental data sets. Giovanni has additional capabilities to alllow users to perform basic analytical operations on these data sets. Giovanni utilizes the Grid Analysis and Display System (GrADS) to perform most of its basic statistical operations.
The primary functions that Giovanni performs are:
- Regional subsetting of global data sets;
- Averaging of regional subset data over selected time periods, displayed in an area plot;
- Display of averaged regional data over selected time periods in a time-series plot;
- Animation of regional area plots for a selected time period; and
- Creation of longitude versus time and latitude versus time "Hovmöller" plots for selected areas and time periods.
Each of these primary functions possesses secondary functions that improve the ease of data handling and the quality of data output and visualization.
— Selection of regional areas for investigation can be done with either a Java map that allows "click and drag" designation of area boundaries, or the areas can be defined via input of latitude and longitude boundary coordinates. The Zoom function in the Java map allows more accurate designation of area boundaries.
— Area data plots are provided with three color scale display options. The "Pre-defined" option is the customary color scale used to visualize the data. [This is the default option.] The "Dynamic" option creates a color scale based on the maximum and minimum data values found in the selected area and time period. The "Customized" option allows the Giovanni user to specify the maximum and minimum values for the color scale.
— Time-series plots are provided with Y-axis scaling options. The X-axis is always time in a time-series data plot. The "Dynamic" option determines the Y-axis maximum and minimum values and the interval tic marks based on the maximum and minimum data values found in the selected area and time period. [This is the default option.] The "Customized" option allows the Giovanni user to designate the maximum and minimum values and the interval for the tic marks. This option enables uniform plot appearance for different time periods and data value ranges.
— The output options are either graphic or numerical. The graphic output option provides a GIF image that can be downloaded and saved. The ASCII output option provides the data in numerical form, based on the Giovanni user specification of the data resolution. The default option is 1.0 degrees, but resolutions as small as 0.1 degrees may be selected.
Additional Giovanni capabilities, such as access and ordering capability for the underlying higher-resolution data files that were used to create the global data sets, are being created. Other Giovanni interfaces allow multi-parameter data intercomparison capabilities. These capabilities will be described in an expanded version of the Giovanni Online Users Manual.