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DISPLAYING AND ANALYZING TOPEX/POSEIDON DATA IMAGES (Macintosh)
There is a large amount of oceans data from the U.S./France TOPEX/Poseidon
mission available on-line which, with some easily accessible software tools, it
is straightforward to view and analyze. Here is the recipe for getting the
software and some data sets in image form and what to do once you have them.
DISPLAYING TOPEX/Poseidon DATA
Once you have the image, launch GIFConverter and open the image. You should see
a Mercator map of the world with land masses in black and bodies of water in
color or gray scale. The image will also be much larger than the size of your
screen.
From the "File" menu, select "Save As..." You do not need to change the name of
the file but you must change the "File Type." In the "Save As..." window, the
file type can be changed by clicking and holding on the "File Type" window,
sliding the cursor down to "PICT" and releasing. This will also change the file
name's suffix from ".gif" to ".Color-PICT." After hitting "Save" you can quit
GIFConverter.
Before launching NIH Image (or just Image), click once on the program's icon and
go to the "Get Info" command in the "File" menu. In the "Memory Requirements"
area at the bottom of the window change the "Preferred Size:" to as much RAM as
you have, minus what your system needs. You can reduce the size of the system
by restarting your Mac with the shift key held down. This will turn the
extensions off. You can find out how much RAM your Mac has and how much the
system needs from "About This Macintosh..." which can be reached from the little
apple in the upper left corner of the screen. Image works best if it has as
much RAM as it can get. Four megabytes works fine, more is better.
Launch Image and open the TOPEX/Poseidon PICT file. The image will be larger
than the screen. The entire frame can be made to fit by clicking on the zoom
box in the upper right corner of the window or from the "Scale to Fit Window"
command in the "Options" menu. You will want to undo this at some point to get
a close look at smaller regions.
ANALYZING TOPEX/Poseidon DATA
Examine the image. Note that there is a key below the image that says what the
colors (or gray scale) mean. Note that the range of data can be very small.
There are several tools in Image that can dramatically increase your ability to
interpret the data. If you ever do something that you can not undo, simply
close the image without saving and reopen it. If you want to save your changes,
use the "Save As..." command so that the original copy remains pristine.
In the "Tools" window find the rectangle with the jagged line running through it
(first column, 8th from the top). Click once on it, then move the cursor on to
a point somewhere on the image. Click and hold and drag the cursor to another
point on the image. What happens? What does the graph indicate? Do the same
thing on the key below the map. Try this in a number of locations around the
map.
When you are ready to try another feature, go back to the "Tools," and select
the dashed rectangle (top of column 2). Go back to the image and drag a
rectangle around a portion of the map. Then go to the "Analyze" menu and select
"Surface Plot..." You will get a window with parameters that you can change.
For now, just hit "OK." Now what happened? Close this new window (don't bother
to save it unless you really want to) and drag a rectangle around the key. Does
the output make sense; is this what you would expect? Try dragging a rectangle
around the letters "JPL" in the lower left corner. Drag a rectangle on the map
and, this time, change a parameter in the window.
Another tool is a horizontal bar with up and down arrows (column 2, 6th from the
top). Click on it and move to the left to the "LUT" or look up table window.
Click and hold somewhere in the LUT and slide the cursor up and down. Now go to
the "Options" menu and click and hold on "Color Tables" and slide the cursor to
the right. Select a new color table by sliding the cursor over the name and
releasing. Go back and try the LUT tool again.
If your computer has enough RAM you can make movies of entire images, subsets or
surface plots. Each frame has to be the same size. Open or create two or more
images. From the "Stacks" window, select "Windows to Stack." The open windows
(until RAM runs out) will be stacked into one window. Then, from "Stacks,"
select "Animate." Use the number keys to control the frame speed. You can save
stacks.
Other tools and menu items you can try include the text and graphics tools to
place text and edit images, rotation, thresholding, density slicing,
enhancements and others. Experiment.
TOPEX/Poseidon INVESTIGATIONS
The TOPEX/Poseidon mission has been underway since 1992 and there is now enough
data to start making some generalizations. But the key to understanding our
planet's oceans and climate is not the raw data that TOPEX/Poseidon provides; it
is the critical questions that we ask ourselves, and that TOPEX/Poseidon data
help us to answer.
In all likelihood, questions that you develop are similar to ones that
scientists are working on answering or are ones that have not been asked yet.
In other words, there is a real opportunity to do real science with these data
sets and tools.
Using the profile tool (the rectangle with the jagged line running through it):
Drag a line across a section of ocean. How can you explain what you observe?
Do the same thing for sections of ocean separated by some land.
Use the "Surface Plot" to do the same type of survey.
By examining the raw data image and the special graphs and plots that you
produce, can you make some statements of why the ocean is behaving as it is?
Are the effects a permanent part of the ocean's character in the regions where
you are surveying or are you observing a unique occurrence?
What are the time intervals of changes? Each image covers 10 days of time so
the effects of tides are averaged out but what happens over 10 day periods; 100
days, 365 days?
How, with the resources at your disposal, can you answer these questions?
Items to consider: currents, major storm systems, current/wave relationships,
wind/wave relationships, ocean floor topography, mixing of warm and cool water
masses, El Nino, seasonal heating, water bodies separated by land, isolated
bodies of water, bodies of water trapped or constricted by land, coriolis
effect...
This is an open ended activity. It will be years before we can successfully
answer many of the questions that we now have. But we can make an excellent
start with the high quality TOPEX/Poseidon data that we have available to us
now.
+ Return to Lesson Plan List
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