May 2002
by Fred Snijders, Roberto Giaccio, Jeroen Ticheler, and Yota Nicolarea
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The following sections provide a step-by-step guide on how to use the Applet. First, the mandatory selections are described, followed by the options that can be activated.
The first thing that has to be done is to select the product for which a chart needs to
be prepared. Currently 3 types of products are supported, each both as dekadal (10-daily)
and monthly values. The products are: Estimated Rainfall, Cold Cloud Duration and
Vegetation Index. The METART site provides further details on origin and characteristics
of the vegetation
index, rainfall
and cold-cloud
products.
Monthly data are in general more smooth than dekadal data and are recommended for first
use.
Crucial to the preparation of the charts is the selection of the time span to use for the x-axis of the chart. Starting and ending month (1-12), and for dekadal products also the starting and ending dekad (1-3), can be selected. The last selection box is for the number of years to chart. When one wants to compare in one chart various growing seasons, such as 1984, 1988 and the average, the year selection should be put on 1. When, on the contrary, the time series of a sequence of years should be examined, say 1984 through 1988, the year selection should be set to 5. Up to 12 consecutive years can be selected.
The sequences determine the individual chart lines and require, for country charting, the selection of the starting year of the sequence and the selection of the zone within the country. The zones can be found on the small map below the charting applet (see next page) and represent the area for which the data available for charting has been extracted. Let us continue with the two examples given under the "selection of the time span". The first example had a base period selection of 1 (one) year. Now this needs the selection of 3 sequences. One with starting year 1984, another with 1988, and a third with "average". The result is given in figure 2.1. The second example, with a time span of 5 years, would need only 2 sequences: one with starting year 1984, and another with "average". See figure 2.2 for the results. On Page 5 of this article, a full Africa version of the Applet is provided. In that case, not only the zone, but also the country has to be selected.
Figure 2.1 - Charting example using a 1-year time span
Figure 2.2 - Charting example using a 5-year time span
The standard behaviour of the Applet is to display a "normal" chart. However, by checking the "Cumulate" box, all data will be added to each other in a cumulative fashion. For instance when for a certain zone the data for January, February and march would be 21, 15, 7, a "normal chart would also show the value sequence of 21, 15 and 7. In a cumulative chart this would be 21, 36, 43, as each new value would be added to the previous one. See Figure 2.3 to see the cumulative version of Figure 2.1, starting from April (month 4). All three figures clearly show the total failure of the growing season during 1984 and the very good conditions during 1988.
Figure 2.3 - Example of cumulative chart
The standard scaling, this is the way the Y-axis is displayed, is pre-determined by the selected product. So all charts showing vegetation index, will have the same scaling, which make inter comparisons of charts much easier. By checking the "Auto scaling" box, a more efficient use of the charting space can be obtained, but at the expense of the ease of comparison.
The button on the right of the selection panel is the "Clone Chart" button.
Clicking this will prepare a copy of chart in a separate window. In this way charts of
various zones or years can be prepared and compared. An example of the result was given as
figure 1.3 in the previous page.
The size of the cloned window can be change as needed.
Proceed to:
Fred Snijders, Roberto Giaccio, Jeroen Ticheler and Yota Nicolarea: Bringing Africa data to the desktop: the ARTEMIS Charting Applet, Page 2.
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