Image Analysis as a Tool for

Inquiry - Oriented Science Instruction

Bob Newton - Geology
Dick Briggs - Biology

General Information

Bob Newton Dick Briggs
Office: Burton 207 Office: Sabin Reed 438
Phone: Ext 3946 Phone: Ext 3823
email: rnewton@science.smith.edu email: rbriggs@science.smith.edu

Software Requirements:
  1. NIH Image
  2. Conversion program to convert images from GIF to TIFF

PRINTING To print out these instructions simply click anywhere in the right hand frame to select it, then use the PRINT command under the FILE menu.

Description

A hurricane has formed in the Atlantic and is heading for New England. Where will it hit? When will it arrive? Is it intensifying or weakening? These are the obvious questions that students ask. Satellite imagery now available on the world wide web gives you the tools to answer these questions. In this workshop you will learn how to use Macintosh computers to access satellite and radar imagery. Downloaded images will be analyzed using the free image analyzing software NIH Image. You will learn how to scale the images and measure distances directly on the computer. The speed of the storm will be determined by comparing the position of the storm from images taken at different times. Multiple images can easily be combined to form animated sequences which show where the storm is heading. Students can make their own forecasts from this data and then watch to see how their predictions turn out.

Images

Hurricane Fran
Download TIFF File Download TIFF File Download TIFF File

Wednesday January 14, 1997 at 5 different times
Download TIFF File Download TIFF File Download TIFF File Download TIFF File Download TIFF File

Satellite Images

The satellite images used in this excercise come from GOES (Geosynchronous Operational Environmental Satellites). The images were downloaded from the internet using the WeatherNet homepage.

Each image is made up of an array of pixels or points, with each pixel being assigned a brightness based on a digital number. These numbers generally range from 0-255 (8 bits) with the highest number being assigned white and the lowest number black. The images are generated from a 5-channel multispectral scanner in the satellite which responds to light in both the visible and near infrared spectrums (IR), thus there are a number of images obtained during each scan. The brighter parts of the infrared image (IR) represent colder, high altitude clouds. The visible image obviously can only be collected during daylight hours while the IR image can be obtained day or night.

The date and time that an image is collected is usually displayed at the bottom of the frame. Time is given in UTC or Universal Coordinated Time also known as Greenwich mean time (Zulu). Eastern Standard time is equal to UTC minus 5 hours.

Viewing Images

Images may be viewed directly within a web browser like Netscape. These images are in either the GIF or JPEG format. However, to make measurements on the images you will need to use image analyzing software. NIH Image is a freeware program from the National Institute for Health which is currently in version 61. A Windows version is in alpha testing. NIH Image requires that the images be in TIFF form, thus to use this software you need to take the GIF images downloaded from the web and convert them to TIFF format with software such as GifConverter which is shareware (nominal fee) that can be downloaded from the web. For today's workshop the images have already been converted to TIFF format for your viewing pleasure.

Using NIH Image

First download the TIFF images you want to examine by clicking on the "download TIFF image" under the picture. When downloading a TIFF file, three files are actually created on the desktop. You should place in the trash the two files ending in HQX and SEA. Then open NIH Image by double clicking on the NIH Image icon on the desktop. To open the TIFF files from within Image simply go to the FILE menu, hold down the mouse button and drag to the OPEN command and release the mouse. You will then be prompted for the location of the files to open. Be sure to open the files in their chronological order.

Aligning Images

You should have opened at least two images collected at different times. Once you have opened at these images then you need to make sure that they are aligned. That is they are superimposed directly on top of each other. If you are using full-size images they will already be aligned. If you use cropped processed images you will probably have to align them by hand. Using the HAND tool click and hold anywhere on the image and drag to move it. To see the next image press the COMMAND and ` keys simultaneously. Use the hand as a reference point and move one of the images until there is no shift in some reference point (state borders) when you change from one image to another.

Creating a Stack

A stack is a sequential series of images which can be animated to show movement of cloud systems. To create a stack simply click and drag down the STACKS menu at the top of the page. Release the mouse button when WINDOWS TO STACKS is highlighted. To cycle through the images you can either use NEXT SLICE or PREVIOUS SLICE under the STACKS menu or their command equivalents command-period and command-comma.

Scaling Image

The image must be scaled before distance measurements can be made. To scale the image first locate and measure a known distance from a map - such as the length in kilometers of the southern border of Wyoming. Then:

  1. On the image draw a line using the dashed line tool in the tool menu bar. The line should correspond to the known distance measured on the map.
  2. Click and drag down the ANALYZE menu until SET SCALE is highlighted.
  3. FIRST SELECT UNITS OF MEASURE (KM) IN THE DIALOG BOX
  4. Then type in the value of the known distance (500 for example)
  5. Click OK

Measuring Distances

  1. Use the NEXT SLICE / PREVIOUS SLICE commands to move to the first image in the stack.
  2. Select the dashed line (measure) from the toolbar. Position the cursor on the point from which you want to measure. Don't click or move cursor after it has been positioned.
  3. Use the NEXT SLICE command to move to the next frame in the sequence. Click and drag the mouse to the corresponding point on this new image, the one you want to measure to.
  4. Click and drag on the ANALYZE menu item at the top of the screen until the MEASURE item is highlighted, then release the mouse button.
  5. Click and drag on the ANALYZE menu item at the top of the screen until the DISPLAY RESULTS item is highlighted, then release the mouse button. A table will appear showing the mean pixel value along the line and the length of the line in the units specified when you scaled the image.

Measuring Area

  1. Use the NEXT SLICE / PREVIOUS SLICE commands to move to the image of interest
  2. Select the dashed freehand line or segmented line (measure area) from the toolbar. You will need to click and hold on the dashed tool icon to allow you to select a different measure tool.
  3. Click and hold the mouse button to draw a line around the area of interest.
  4. Click and drag on the ANALYZE menu item at the top of the screen until the MEASURE item is highlighted, then release the mouse button.
  5. Click and drag on the ANALYZE menu item at the top of the screen until the DISPLAY RESULTS item is highlighted, then release the mouse button. A table will appear showing: the area of the region outlined in square units specified during the scaling process; the mean pixel value within the area you outlined; and the perimeter length.

Creating a Movie

Images within a stack can be animated by simply using the ANIMATE command under the STACKS menu. The speed of the animation is controlled by the number keys on the keyboard with 9 giving the highest speed and 1 the lowest speed. To get the proper effect the images must be loaded in sequence before the stack is created. The best results are obtained when there are many images collected at hourly intervals.

Questions

  1. What can you see on a satellite photo?
  2. How does a storm appear on the image?
  3. How does it change from one image to another?
  4. How might you estimate the intensity of the storm?
  5. How can you determine how fast the storm is moving?
  6. How can you determine where it is heading?
  7. How can you determine when it might arrive?

Weather Web Sites


Image Analysis Web Sites