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I recommend you work through this document in order, while experimenting freely; send comments and suggestions to me at n-g@tamu.edu.
To set up McIDAS, follow the instructions in the McIDAS setup tutorial. If you haven't run McIDAS in a year or so, you may need to do this; some of the files have changed and the software has been updated. To determine whether you need to go through the setup, just try running mcidas. If you find that you can't load images or other such problems, go to your home directory, rm -r mcidas, and proceed with the setup tutorial.
and you should successfully exit McIdas. Don't worry about the capital letters; McIdas commands are always in capital letters, unless you actually try to capitalize them.
So if the command worked, type
mcidas
again to get back in.
The third McIdas window is small and blue, with a set of menu options. this is the menu window. This window also enables you to communicate with McIdas. Unlike the command window, though, you don't have to type long strings of seemingly random letters to get McIdas to do something. On the other hand, there are lots of things you can do with McIdas that you can't do from the menu window.
A common, but harmless, McIdas mistake is to type commands in the blue feedback window rather than the command window or menu window. McIdas will sit there smiling at you, with you smiling back and wondering why nothing is happening. Remember that McIdas wants the mouse to be in whatever window you're typing to.
Other window manipulations work just like any other windows in the SGI environment. To move a window, hold down the middle mouse button while the mouse is pointing to the edge of the window. To bring a window to the top, click on the left mouse button while the mouse is pointing to the edge of the window.
The menu window, as it initially appears, has about twenty options. Unfortunately for you, only one of them works. This is the option labeled F1, Latest Images/Image Loops. The F1 represents the function key F1 along the top of your keyboard. Go ahead and hit the F1 key while the mouse is inside the menu window and you should get a different set of menu items, entitled "Latest Images - Menu".
The F1 key, for example, is now listed as GOES-East Visible. Try hitting the F1 key again (with your mouse inside the menu window) and see what happens.
The first response should be a line in the command menu that begins with the word "ALOOP" and continues on with a meaningless string of characters and numbers. After a while, a few more lines of text will appear. Meanwhile, an image (preferably a GOES-East Visible image) will also appear in the image window, with a map and a brightness table soon to be overlain. Congratulations, you have your first image.
At this point, you may wish to experiment a bit and see what some of the other options do. Included in the list are options F1 through F9, and options SF1 through SF6. The latter options are accessed by holding down the Shift key while striking the appropriate function key. Don't forget to have your mouse in the menu window. If no ALOOP command appears in the communications window, your keystroke didn't take.
For your next exercise, start with the latest GOES-West Infrared image (F5). Now notice the two options down below the main section. One is activated by CF12 (Control + F12) and controls looping. The second is activated by SF12 (Shift + F12) and allows for additional user input. Try the first one. Hit CF12 now. The status should change from LATEST to LOOP. Now hit F5 again to reload the infrared imagery from the west coast. Then, sit back and watch as the latest ten or so hourly infrared satellite images are loaded into the mcidas window.
So far, you haven't done anything that you wouldn't be able to do from a good web site, except that it's been somewhat more complicated than it would be at a good web site. However, through mcidas, you have complete control over all aspects of the image, from navigation to resolution to enhancement to looping speed to time interval. For your first taste of this flexibility, hit SF12 (Shift + F12) now. You should thereby have turned user-defined load ON. (Check the menu window to confirm.)
Now hit F5 again. After a little bit you should get a new window called the Center/Blowup/Blowdown Selection window. I'll call it the Blowindow. Let's now use it to look at whatever storms are crossing the International Date Line. To do this, specify the center of the image in latitude and longitude. By default, West and North are positive. So you might enter 40 160 for the Load Center. Now click Load to see what happens.
Well, not much happens for a while, except for another aloop line showing up in the communications window. Then, eventually, you should get a loop of storms crossing the Dateline. You can control the looping with the looping control buttons. When you're done with this set of images, click on Done.
Let's try another. How about a visible closeup of College Station? For this, let's use the visible composite: F7. You'll also want to specify the load center to be CLL and the LIN blowup/blowdown factor to be 3 to get a good closeup.
Note that as you zoom in more, the image doesn't actually become clearer. You're limited by the resolution of the data as we receive it. For a different effect, try a factor of -2 and watch the sun rise.
Again, go ahead and experiment a bit. Have a look at features that interest you. You may find that for most of what you want to use McIdas for, the menu options are perfectly satisfactory. The rest of this tutorial describes the command line interface: much more flexible and powerful, but more difficult to learn and remember.
To advance one frame, type A. To back
up one frame,
type B. To start a loop, type
L.
(Not very exciting without any images, but at
least you can watch the little yellow number increment.) To stop the
loop, type L again.
By the way, any one-character command can be abbreviated by holding down the Alt key while typing the character. This saves hitting a carriage return and is convenient for rapid-fire loop manipulation.
ALOOP 1500 1547 1 9
This command will do it all for you. Sit back and enjoy the show. It will think about stuff for about fifteen seconds, then start generating images.
Perhaps you'd like to know something about the syntax. The 1500 and 1547 specify the "area files" (mcidas image files) from which to read the satellite data. Each set of ten files corresponds to a different set of imagery. The breakdown is:
If you'd like, try the command now with a different set of area files. For example, to get the West Coast water vapor imagery, type
ALOOP 1700 1747 1 9
The next two numbers specify the first frame and maximum number
of frames to load. The maximum number should generally be 9;
ALOOP will
load as many frames (up to the nine most recent) as it can find for the
current day. The first frame
would be 1 unless you already have a loop starting at frame 1 and don't
want to nuke it, in which case the initial frame might be 11 or something.
While we're on the subject of West Coast imagery, this is probably
a good time to mention an additional option of ALOOP
that lets you center
the image wherever you want. If you have the water vapor loop up, you
have noticed that it's long on Pacific data and short on North America.
To display something more relevant to Texas, type
ALOOP 1700 1747 1 9 EC SFO
to center the image on San Francisco and thereby get more of North America displayed.
Another thing you might want to try (if you have the patience) is
loading more than nine frames.
To do this, yo must change both the maximum number of frames and the
LIMIT parameter, which specifies the maximum number of hours
to search backward (it defaults to 8). For example,
ALOOP 1300 1347 1 16 LIMIT=24
will (if the data is complete) load the most recent 16 frames of West Coast infrared imagery.
If you really want to know more, type HELP ALOOP.
But this is only if you're really serious. If you're merely humorous,
you can learn a lot from the syntax by examining the form of the
ALOOP command that is issued when you use the function keys. You
will find that it is possible to change the location, the magnification,
the enhancement, the map, and the looping.
L,
A, and B commands,
which were described earlier. This section is for more advanced loop
control techniques.
LB command
LB
and examine the Image Frame= line. You should see frames 1 through 9 listed if you're lucky, or 1 through some smaller number if you're not so lucky and there are frames missing.
Suppose you only want to loop over the last five images. If those images are in frames 5 through 9, you could type
LB 5 9
to accomplish this task. You won't actually see a loop running unless
you already have it looping. Remember, the L command turns
looping on and off.
A little experimentation will show you that A and
B will only take
you to the edges of the loop and no farther. To look at frames not in the
current loop, you should set the loop boundaries to encompass all frames
by typing
LB 1 32
LS command
LS command. In this example, you could type
LS 1 2 3 4 6 7 9
and thereby obtain a clean loop.
Alternatively, you may wish to set up a forward-backward loop. You could do this by typing (if there are nine frames in your loop)
LS 1-9 9-1
DR 1
Or, if you want to be specific, like making the first and last frames dwell longer, you could type something like
DR 8 2 2 2 2 2 2 2 8
if you have nine frames, or something analogous otherwise.
As with any command, I'm just giving you the tip of the iceberg. You can use the online HELP to find out more.
The color table is a one-to-one mapping of brightness sensed by the satellite to colors (or gray shades) displayed on the screen. Except perhaps for visible imagery, no color is "correct" for a given image, although some are more conventional than others.
The standard scale is IMAGE. But there exist other color tables besides IMAGE. For example, a common enhancement curve for infrared imagery is the MB enhancement curve. You can apply the MB enhancement curve to images 1 through nine with a command like
EU REST MB 1 9
If you leave off the numbers (1 9), only the current frame
is affected.
For hours of endless fun, you can make your own color table. Or you can go right in and specify which colors will correspond to which brightnesses. The total range of brightnesses is 0 to 255. You can read the help for details, but I'll give you one example here. The water vapor imagery tends to be really washed out, so you can increase the contrast by assigning 210 to white and 140 to black, with a smooth gradation in between. To accomplish this with water vapor images in frames 1 through 9, type
EU MAKE 140 210 BLACK WHITE 1 9
and you'll be able to see structures you couldn't see before.
Any of the manipulations described above can be undone by typing
EU REST IMAGE 1 9
or whatever numbers correspond to the beginning and ending of your loop.
Lots more can be done with the EU command; see the
help if you're interested.
This is a good place to stop and play around with some of the commands you've learned. I suggest that you check out some of the other area files, and acquaint yourself with the various types of images that we receive on an hourly basis at Texas A&M. When you're ready, or if you don't like suggestions, you may continue.
ALOOP does a lot of stuff automatically, but there may come a time
when you want to take control and strike off on your own. That's what
this section is for. I'll tell you how to select a current image and
display it exactly the way you want. For the purposes of this example,
let's suppose you're particularly iinterested in the infrared cloud pattern
over Montana.
First, how to read the title on the bottom of a McIdas image. Here's a sample title:
0001 G-8 IMG 01 6 FEB 96037 161500 02805 09049 08.00
Frankly, I don't know what all of it means, but from left to right, you have the frame number; the satellite/image identifier, the wavelength band (01 = visible, 03 = water vapor, 04 = standard infrared), the date, the year and Julian day, the time (GMT), and the latitude and longitude in hundredths of degrees of the center of the original image (not necessarily the center of the portion of the image which is displayed). The last number, I don't have a clue.
LA command
LA 1400 1447
will give you the list of current Goes-8 visible images. Some of the numbers correspond to the legend displayed on the bottom of the image window; the rest you don't have to worry about. From this list, you can check the year, Julian day, and times, and identify which area number corresponds to the most up-to-date image. At the time I'm writing this, the most up-to-date image happens to be image 1446, so I'll use this number in the rest of the example. If you're doing this at night, the most recent image might be pitch-black, so pick something from during the middle of the day.
If the communications window was not tall enough to see the complete list of images, then just make the communications window bigger by dragging the top or bottom edge of the window with the left mouse button.
IMPORTANT: Note that the most recent image is not listed on the bottom. The images have 48 slots, and recent images overwrite earlier ones. You have to actually read the yyddd (year and Julian day) and hhmmss (the time in greenwich) to locate the most recent image embedded within the listing.
DF command
DF command in its simplest form:
DF 1446 1
places image area number 1446 into frame 1. Note that you actually have to
go to frame 1 (with a suitable combination of L's,
A's or B's) to see the image.
Unfortunately, this image is centered on the East Coast, and I care more about Montana. There's a command which centers the image over Great Falls:
DF 1446 1 EC GTF
but all that does is move the image so that Great Falls is in the middle of the window. Since the image doesn't extend very far to the north and west, you just get lots of blank space along the top and left margins of the window. So that doesn't really help much.
Our next move is to magnify the image, to zoom in onto Great Falls. This requires only a minor modification from the previous command:
DF 1446 1 EC GTF 2
The 2 tells McIdas to magnify the image by a factor of 2.
Any realistic number can be used here, but if you magnify it too much,
you begin to see the individual pixels instead of the cloud pattern.
Try typing MAP again. If you are zoomed in enough,
McIdas decides that you are ready for state boundaries.
Also, you can append a magnification number to your ALOOP
command, if you so desire.
MAP and EG commands
MAP
If you like latitude/longitude lines, try
MAP LALO
If you want to be specific about the latitude/longitude interval, try something like
MAP LALO INT=5 10
If you use LALO, you won't get the rest of the map (such as coastlines or political boundaries) drawn, so just issue the command twice if you need to, once with LALO and once without. If you're easily bored, you will also want to erase the map on occasion. The command which erases the graphics on the current frame, but leaves the image intact, is
EG
AAMAP command (we're getting serious now)
If you're in METR 452, skip the next paragraph. If you're not in METR 452, read the next paragraph and skip the paragraph after it.
What I'd really like to do is remap the image to a polar stereographic projection centered over Great Falls and zoom in a bit. The command to accomplish this and pop the result into frame 2 is
AAMAP 1446 3001 2 PS 47 112 8
Try this, advance to frame 2, overlay a map with the latitudes/longitudes of your choice, and compare the two frames. You will find that it's a lot easier to see the cloud structure in the remapped image.
Those of you in METR 452 need to know something about the AAMAP
command first. Basically, it generates a new area file. Bad things will
happen if more than one person tries to write to the same area file. So
you must pick a unique area file number. You should use something between
3000 and 3947. To make sure you don't use somebody else's number, write
down the number you choose on the whiteboard in 1201 in the space provided.
After you do this, you can issue the command (replacing nnnn with the number
of your choice):
AAMAP 1446 nnnn 2 PS 47 112 8
Try this, advance to frame 2, overlay a map with the latitudes/longitudes of your choice, and compare the two frames. You will find that it's a lot easier to see the cloud structure in the remapped image.
Okay, everybody back on the same paragraph? Good. Now let me explain the command syntax. The first number is the source image file number. The program will take that image, remap it, and write it to the file corresponding to the second number. It will then display it in the frame corresponding to the third number. The PS 47 112 tells it to use a polar stereographic projection centered on 47 latitude and 112 longitude (North and West are defaults). It also understands projections LAMB and MER (Lambert and Mercator). The last number is the resolution, in kilometers. 8 is the original resolution, so smaller numbers will give you closeups but will look grainy.
You have the ability to construct a loop of remapped images. To
avoid creating lots of remapped files, you should use the same destination area
number for all images, and wait until each image is loaded before issuing
the command for the next one. The following sequence will display remapped
images, with map backgrounds, in frames 11 to 14. METR 452 students should
use their own destination numbers, represented by nnnn in the above
example. Unless you're really gung-ho, I recommend only a loop of 4 or 5
images if you want to try this one out.
LB 11 20 AAMAP 1443 3001 11 PS 47 112 8 MAP A AAMAP 1444 3001 12 PS 47 112 8 MAP A AAMAP 1445 3001 13 PS 47 112 8 MAP A AAMAP 1446 3001 20 PS 47 112 8 MAP L
EXIT command. As with any weather program, don't delete any of the
windows yourself.