GEO 243 - Remote Sensing
Lab Activity 3
Image Acquisition, Preprocessing, and Windowing

In this lab activity we will use the Internet to connect to an online satellite data archive and download a Landsat ETM scene (of your choice).  We will decompress the files that are downloaded and use the "import" module in Idrisi to create Idrisi images.  We'll then extract a window from the multiple channels we have downloaded and create an enhanced color composite of this image.

We begin with a visit to the Global Land Cover Facility hosted by the University of Maryland.  This site provides easy access to a massive collection of Landsat, EOS, MODIS, AVHRR, and other civilian image datasets.

Landsat Scenes: 28,558
MODIS Composites: 235
ASTER Scenes: 803
Total Size: 13 Terabytes

(as of spring 2007)

The facility is located on the web at:

http://glcf.umiacs.umd.edu/index.shtml

The site provides intuitive tools for delivering data in a very usable format.  Under "Download Data" click the link to the ESDI and you'll be directed to the Earth Science Data Interface.  The data interface presents three options:

Select the "Map Search Option".  This presents an easy to use map interface:

Use the tools at the top to zoom, pan, and select images.  On the left is a control set that allows you to select different image products:

Use the zoom tool to zoom to a particular part of the map that you may have an interest in.  Think of someplace you've been in the world that you would really like to see in a satellite image, perhaps allowing you to relive that special summer... Zooming can be done with successive clicks of the magnifying glass tool, recentering and zooming with each click:

On the left side of the screen select the "ETM+" box and click "update map".  You also have the option of selecting TM and MSS scenes that go all the way back to 1972 here.  This action should present a screen that has framed outlines of particular scenes on your previous map:

Use the select tool to select a particular scene.  If, for some reason, there is no ETM scene available for a particular site, try another one.  When you have selected one or more scenes, click to "Preview & Download" link.  This will open a preview window with a "browse" or preview image of the scene you have selected.  This is used to check the quality, cloud cover, and coverage of the scene:

It has information about the date, data type (make sure you have GeoTIFF) and location of the image.  The format of this information is something like this:

Click on the "Download" button and an FTP window will open with downloadable links for the multiple channels available for the image:

The linked files on the left can be download to a folder you have created.  Note, the filenames indicate the path/row, satellite, sensor, date, and channel.  For example, in this folder (shown above, the first two links are low and high gain thermal IR, the third line is 15 meter pan, and the section of large files at the bottom are each 30-meter TM channels.  These files are compressed (zip) GeoTIFF files.

NOTE: THESE ARE RATHER LARGE. WHEN YOU START MOVING THESE AROUND, SAVING THEM TO HARD DRIVES, OR MOVING THEM TO FLASH DRIVES THEY WILL TAKE SOME TIME.  BE PATIENT, AND DO NOT MAX OUT YOUR FLASH DRIVE SPACE.  I highly recommend that you do all of the work on your HARD DRIVE up until you create the windowed images - YOU have limited flash drive space. After creating the windows you can copy them to your flash drive if need be.

When you have saved at least three (3) of the 30-meter channels to your C-drive, double click the files and decompress them using the WinZip application (more on this in class).  Decompress the TIFF files to your folder.

After you've done this open Idrisi and create a new project, setting the default folder to the one you created for your downloads.  Use the FILE-IMPORT-GOVERNMENT DATA PROVIDER FORMATS-GeoTIFF module to convert these GeoTIFF files into Idrisi image files.  After converting these files dispose of the ZIP (gz) files and the original GeoTIFF files to save drive space.

Now use the REFORMAT-WINDOW module to extract windows from each channel you downloaded of an area of interest.  Here is some information about the WINDOW module:

WINDOW extracts a sub-image from an original image to a new image, or sub-image windows from a whole set of images. It may be used to isolate a study area, or to break large images into smaller parts for processing.  WINDOW first requires the name(s) of the image file(s) you will be extracting from. You also have the option of specifying a Raster Group File (.rgf). If entering the images individually, select the number of files to be used using the spin buttons and enter the filenames in the grid. Alternatively, you can enter in the filenames using the layer group option.  Next, enter a name for the output image or prefix if you have multiple input images. You must choose to specify the window to be extracted by row and column positions, geographical positions or by an existing windowed image, for which you must enter a file name. You must then define the row/column or X/Y coordinates of the area to be windowed out.

If applicable, enter the header size (this is optional).

1. Columns and rows are numbered from 0, with the rows progressing from the top to the bottom.

2. To extract a rectangular region that is not oriented in the same direction as the grid of the original image, use the RESAMPLE module.

3. To extract an irregular polygon, use QUERY.

4. You may interactively select a window in the display with the zoom window tool. To save this window as a new image (or in several other formats) use the Save Composition function on Composer.

The WINDOW dialog looks something like this:

When you've defined the area you want to create your window for, extract identical windows from all available channels for the channels that you downloaded.  These should go into the original folder you created.  Note that you should use column and row specifications to define your windows and that you can create your windows all at the same time.

Now, create a 24-bit color composite (remember??) from the windows you extracted from the original channels.  Hint: Omit the zeroes in your stretch when creating the color composite.  Remember, these files are quite large (~ 3 times as large as each window).  Conserve space!!

Print your color composite as a C-size image and label it with the location of the image, channels used, date of the image, scanner and satellite, and place your names in fine print at the bottom right corner. Aces..

This lab activity is due at the beginning of class, Thursday May 7.