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7.9 Plotting time-series along tracks

A common application in many scientific disciplines involves plotting one or several time-series as as ``wiggles'' along tracks. Marine geophysicists often display magnetic anomalies in this manner, and seismologists use the technique when plotting individual seismic traces. In our example we will show how a set of Geosat sea surface slope profiles from the south Pacific can be plotted as ``wiggles'' using the pswiggle program. We will embellish the plot with track numbers, the location of the Pacific-Antarctic Ridge, recognized fracture zones in the area, and a ``wiggle'' scale. The Geosat tracks are stored in the files *.xys, the ridge in ridge.xy, and all the fracture zones are stored in the multiple segment file fz.xy. We extract the profile id (which is the first part of the file name for each profile) and the last point in each of the track files to construct an input file for pstext that will label each profile with the track number. We know the profiles trend approximately N40°E so we want the labels to have that same orientation (i.e., the angle with the baseline must be 50°). We do this by extracting the last record from each track, paste this file with the tracks.lis file, and use $AWK to create the format needed for pstext. Note we offset the positions by -0.05 inch with -D in order to have a small gap between the profile and the label:

    #!/bin/sh
    #               GMT EXAMPLE 09
    #
    # Purpose:      Make wiggle plot along track from geoid deflections
    # GMT progs:    pswiggle, pstext, psxy
    # Unix progs:   $AWK, ls, paste, tail, rm
    #
    ps=example_09.ps
    pswiggle track_*.xys -R185/250/-68/-42 -U"Example 9 in Cookbook" -K -Jm0.13i -Ba10f5 -Gblack \
            -Z2000 -Wthinnest -S240/-67/500/@~m@~rad > $ps
    psxy -R -J -O -K ridge.xy -Wthicker >> $ps
    psxy -R -J -O -K -m fz.xy -Wthinner,- >> $ps
    rm -f tmp
    # Make label file
    for file in track_*.xys; do
            tail -1 $file >> tmp
    done
    ls -1 track_*.xys | $AWK -F. '{print $2}' > tracks.lis
    paste tmp tracks.lis | $AWK '{print $1, $2, 10, 50, 1, "RM", $4}' \
            | pstext -R -J -D-0.05i/-0.05i -O >> $ps
    rm -f tmp tracks.lis .gmt*

The output shows the sea-surface slopes along 42 descending Geosat tracks in the Eltanin and Udintsev fracture zone region in a Mercator projection (Figure 7.9).

Figure 7.9: Time-series as ``wiggles'' along a track.

Next: 7.10 A geographical bar Up: 7. Creating GMT Graphics Previous: 7.8 A 3-D histogram Contents Index