Introduction to Remote Sensing
Purpose: To learn about how remote sensing data is collected,
transmitted and used. To become familiar with the types of remote
sensing data that are now readily available on the web and to learn
to interpret, analyze and enhance maps produced with remote sensing data.
To introduce appropriate 2-D area rendering techniques for remote sensing
Overview: Remote sensing data has become very important
in a number of scientific fields. In this lesson students view, discuss,
and compare different types of maps produced from remote sensing data.
Then using image processing software they analyze and enhance sea surface
temperature maps. Only a brief introduction to remote sensing data is provided
in this lesson. There are many excellent internet sites on this topic.
If students have internet access this makes a great research and presentation
topic. Once students are familiar with the images available and the
image processing software they can also develop good portfolio projects
applying these techniques.
Scientific Visualization: 2 D Area rendering techniques
Science: Earth Science: location and mapping,
meteorology, oceanography, space exploration, current research.
and Technical Visualization Objectives:
This lesson serves as an introduction to some of the software and techniques
needed for the following level II objectives:
2.01B The student will identify and apply the guidelines
for 2-D color usage.
3.01 Identify and explain 2-D area rendering
The student will identify sources of data and applications
for 2-D area rendering. The student will identify and apply color lookup
table techniques. The student will identify and apply image processing
techniques. The student will identify and apply measurement techniques.
The student will identify
and apply output techniques.
and Environmental Science Goals and Objectives (objectives from 1994 revision):
Work on this lesson can contribute to understanding
in the following areas:
2.14 Demonstrate the ability to formulate models
5.2 Demonstrate knowledge of current
research in earth/environmental science.
6.1 Demonstrate knowledge of mapping
skills and location of points on earth.
8.3 Demonstrate knowledge of weather
9.1 Demonstrate knowledge of ocean
and estuarine circulation.
The directions included in this lesson are for Scion Image Release Beta
3b for Windows NT. Directions may need some adjustment for NIH Image
or other versions of Scion Image. Teachers should be sure to do this
project several days in advance on the computers the students will be using
to check for adjustments in the directions. This lesson can be done without
internet access but will be much enhanced with internet access.
Image or NIH Image, Internet Access
Remote sensing provides many types of scientists with data about
our earth and beyond. In this lesson we will be concentrating on
the data about Earth provided by satellites. These satellite images
used to be available only to government agencies and advanced research
centers but now much of the data is available to the public. Some
data such as sea surface temperatures and weather maps can be accessed
in near real time on the web. Other satellite images can be
ordered in digital form by anyone with web access. The data can be
analyzed for a wide variety of projects. A quick summary of
how remote sensing works and what it is used for is provided below for
teacher reference and for those classes without internet access.
For those classes with internet access, links are provided in the Reference
Section so that students can research these topics further.
An important source of remote sensing data is satellites.
Satellites have sensors which collect data and record electromagnetic
radiation from the Earth. The electromagnetic spectrum is divided
into regions based on the wavelength of the energy. For example,
visible light has short waves compared to radio and TV waves. Satellite
sensors can detect one or more of the types of electromagnetic radiation
that are reflected from or emitted by the Earth. These include visible,
and infrared radiation. Also, some satellites send out radiation,
either radio or light waves, and record the signal that is reflected back.
These systems are called radar if they use radio waves or lidar
if they use light waves. The satellites collect the data and send
it to earth in digitized form. (To help students understand how this
works try the pixel transmission activity).
These different types of data can be used to assess temperature,
weather conditions, type, amount, and health of vegetation, ozone
levels, volcanic eruptions, polar ice melting, etc. For example, thermal
infrared radiation can tell us the temperature of the surface emitting
the radiation which can be used to construct sea surface temperature maps,
cloud top temperature maps, and volcano hot spot maps. By comparing
images taken of the same place over time we can detect patterns of change.
The data is called multispectral if data from more than one part
of the spectrum is collected simultaneously. When this data
is displayed different colors are used to represent data from different
spectral regions. If the spectral regions being displayed are all
in the visible light region and the display uses red, green and blue
to represent the red green and blue light recorded by the satellite sensor
then the image is true color and will look like a photograph.
However most satellite images are not true color. A false color
composite uses different colors to represent the different bands -
for example red might be used for data from the near IR, blue for
the far IR, and green for ultraviolet. You can experiment with using
different colors to display data at the Virtually Hawaii's Spectral Imager
which is part of their excellent online guide to remote sensing.
In a psuedo-color image the color of each pixel depends on the value
of one measured quantity. The sea surface temperature picture
displayed below is an example of a psuedo-color image from NOAH.
In this image the color of each pixel depends on the water temperature
which was calculated from the satellite data. We will be using this
image in the exercises below.
Sea Surface Temperature
Remote sensing is a great topic to research on the internet as lots
of tutorials and interesting images are available. It would be far
preferable to have students research these topics themselves. If
Internet access is available divide students into groups and have them
research and report back to the class on the following:
The Electromagnetic Spectrum
Types of Satellite Data
Displaying Satellite Images
Weather Map Symbols
Remote Sensing and Volcanos
Remote Sensing and Climate Change
Images of the Gulf Stream
Once students have an idea of what remote sensing data is, what it is
used for, what data is available, how it is collected, and if possible
where and how to to find it on the internet they are ready to work with
some actual images. These directions are designed for the sea surface
temp image that you can download here but would work with minor modifications
for other images you or your students might be interested in. Your
browser may give you a choice between opening this file or saving it to
disk. Save it to disk and then open it using Scion Image or NIH Image.
There are several difficult concepts for students to understand in this
exercise. Depending on their mathematical proficiency, students
may need help understanding what is being done when the scale
calibration is done. A possible way to teach this is to use thermometers
which can be read in both ºF and ºC. Help students
to understand the conversion between these two scales which are being used
to measure the exact same thing. Have them note that there
are 180ºF between freezing (32ºF) and boiling (212ºC) on
the Farenheit scale while there are 100ºC between freezing and boiling
on the celcius (centigrade) scale. This gives us a ratio of
180 to 100 which reduces to 9/5. So each rise of one degree celcius
is equivalent to almost a 2 degree (9/5) rise in degrees farenheit.
Since 0ºC = 32ºF the formula for changing celcius to farenheit
is F=(9/5)C +32. Essentially we go through the same process in calibrating
our temperature scale for this image only we are converting pixel values
to degrees celcius. Also we only have to convert 2 measurements.
Once these two measurements are entered into the computer the software
fits a straight line conversion equation and can give you the temperature
for any other pixel value.
The density slice from 24 to 27 degrees Celcius nicely outlines
the gulfstream as shown:
At the end of the directions for the various operations is a list products
you can ask students to do as assignments to turn in or present and
questions to assign or discuss.
The reference section below contains
a list of links to get started finding data, down loading images
and researching remote sensing.
The Gaia Crossroads Project Guidebook to Using Satellite Imagery In
the Classroom and Community. edited by Cynthia B. Ericckson and
Janet W. Campbell is an excellent source of information about remote
sensing and using remote sensing images in the classroom. For
ordering information check out the Gaia Crossroads Project website
Sea Surface Temperature
Satellite Images from NOAA's geostationary satellites - up to date infrared,
visible, and water vapor at http://www.goes.noaa.gov/
The National Climatic Data Center with links to all kinds of radar
and satellite data, including archived data and some explanation of the
North Carolina's climate office with more local data including air pollution,
forecasts and links to many other sites http://www.nc-climate.ncsu.edu/
Volcanic hot spots
NOAA's Coastwatch program has near real time and archived Sea Surface
temperature images available at http://www.bea.nmfs.gov/
You do have to register to get this data but it is free for educational
Remote Sensing Online Lessons
Students can monitor erupting volcanos in near real time! Plus information
on the remote sensing images that allow scientists to do this http://volcano1.pgd.hawaii.edu/
Student Assignment Sheet
- link to separate page for separate print
Remote Sensing - Image Processing
Purpose: To interpret, analyze and enhance maps produced
with remote sensing data. To introduce appropriate 2-D area rendering
Tools: You will be using Scion Image, an image processing
and analysis tool. When you first enter Scion Image four tool and
information boxes will pop up in addition to the Menu Bar.
These are the LUT or look up table which assigns colors to pixel values,
the Toolbar, The map box and an information box. You may need to
click on the full page button to get Scion image to cover your desktop.
Some of the tools you will be using are labeled below. Information
about the others can be found in the contents under tools in Scion's help
Getting Started Download the sea surface temperature image
provided. If you are online, click here to go back to
the download image directions. If you are not online your teacher
will have downloaded the image.
Open this image in Scion Image. The original name of the image
was s9900709.ns7 The s is for the Southeast region, 99 is the year,
007 is the day of the year (the days are numbered from 1 to 365 so the
month is not included in the filename. The 9 means that the picture
was taken between 9:00 and 10:00. The image has been converted to
a special tiff file for you to work with. (Warning:
if you try to download and use the files direct from coastwatch you will
lose some of the information and some of the exercises below will NOT work
properly although they may appear to.)
The n stands for North Carolina and the s7 stands for night sea surface
temperature. Each pixel in this image represents a 1.41 km square.
The average temperature of the sea surface for this area was determined
from the satellite data and stored as a value for that pixel. Each
temperature value then has a color assigned to it.
Examine the image closely. The Latitude and Longitude grid
have been overlaid on the map. The land, interior water surfaces,
and some clouds over the ocean are blue - only the sea surface areas have
accurate temperature data in this image. Note that the sea surface
temperature gets warmer as you go offshore. This is because
of the gulf stream which brings warm water from the tropics north along
Use the magnifying tool to examine the outer banks more carefully.
By clicking on the magnifying tool and then on the image you will zoom
in. When the image is larger you will no longer be able to see it
all at once but you can use the hand tool to move it around. Eventually
if you keep zooming in you will see that the image is made up of pixels.
In this case each pixel represents the average temperature calculated for
a square 1.41 km on each side. Zoom out again by holding down the control
key while you click the magnifying tool.
Measuring Distance: You can use the tools to measure
distances in the image if you calibrate the distance scale first.
We will measure the length of North Carolina's coast. To do this:
Experimenting with the LUT: LUT stands for look up table.
Images are stored as tables of values. In this case each value
is the average temperature for 1.41 square kilometers each of which is
represented by one pixel in the image.The computer uses the LUT to
see what color each temperature value should have. You can
change the LUT. This will change the appearance of your picture
by changing what color is mapped to a particular temperature. It
will not change the actual temperature data.
Pull down the Analyze menu and go to set scale. A dialog box
Change the units to kilometers.
Change the measured distance to 1 pixel and the known distance to 1.41because
each pixel is known to represent an area of 1.41 square kilometers.
The pixel aspect ratio is 1 because our pixels represent the same distance
for the length and the width. .
Now you can measure distance with a line selection tool. If
you hold down the mouse button you can choose a freehand or segmented
line as well as the straight line. Because the coast is irregular
the freehand tool will allow you to trace the coastline most accurately.
Choose the freehand tool, start at the state line with Virginia and trace
along North Carolina's coast and the Outer Banks down to the State line
for South Carolina. The line will disappear as soon as you release
Pull down the analyze menu and choose measure.
Then (also in the analyze menu) select show results.
A results dialog box should pop up. Since your line has no width,
area and mean will be 0. The length should be approximately 600 km.
You can go back to set scale and change the scale to miles by just changing
the units to miles. Re measure and find that the coastline is approximately
380 miles long.
You can use the select rectangular area tool to find the area of a selected
region as well.
Featuring North Carolina
Under the Options menu you can change to gray scale or any of several
other LUTs listed under color tables. You can also invert the LUT
under the LUT options menu choice. Experiment with these different
options noting the advantages and disadvantages of various choices.
You can always go back to your original image by choosing revert to saved
in the file menu. If you decide to save any other version of your
map be sure to use save as and give it a different file name.
There are several other ways to manipulate the LUT. You can use the
box (choose it under the window menu if it is hidden) to
adjust the brightness and contrast. You can use the little sliders
or the line graph. Practice this with a gray scale image. Notice
what happens to the grayscale LUT when you adjust the contrast and when
you adjust the brightness. (question 4)
You can move whichever LUT you have selected directly. With
the LUT tool selected click and hold on the LUT. As you slide the
LUT up and down different color ranges are used.
Calibrating your temperature
scale: This operation allows you to give Scion Image the
information to calculate the temperature scale. Each pixel in the
image has a value between 1 and 255. The temperature range
that the image was transformed with was -5 to 35 ºC. (Temperatures
outside the chosen range would map white or black.) So a temperature
of -5ºC gets a pixel value (P) of 1 and a temperature of 35ºC
gets a pixel value (P) of 255.
The index number of the pixel value used to overlay the state border lines
and rivers is 4. To make these borders and rivers stand out clearly
you can map that value to a different color. Choose the eyedropper
tool. Move the cursor over the LUT - you should see the index value
change from 0 at the top of the LUT to 255 at the bottom. Get the
value to exactly 4 and double click. Now choose a color for state
borders and rivers. In the same way you can choose a different color
for the latitude and longitude lines. Their index value is 2.
If you have a lot of patience you can use the paint bucket
tool to fill in North Carolina's land area with another color of
your choice. This will help orient the viewer by allowing him or her to
distinguish North Carolina from the surrounding states. You
will have to use the zoom tool and the pencil tool to be sure that the
land area is completely enclosed by lines. Otherwise your color
will leak out along the coast. When that happens you can use undo
or revert to saved until you get it right. You will also need the
zoom tool if you decide to work on the Outer Banks.
Use the text tool to label the rivers.
This gives us a conversion formula, where P stands for Pixel
ºC = (40/255)P - 5
So what you have to do is:
Use the select region tool to select a small area just a few pixels
square, someplace in the ocean.
Select measure in the analyse menu.
Then select calibrate in the analyse menu. A pop up menu will come
up with the average measured pixel value for your square. This is
Substitute the measured value for P in the conversion equation above to
calculate the degrees Celcius. (You can do the math with a calculator
- your computer probably has one you can use in the Accessories folder.
(look in the start menu in the programs menu for accessories then look
Enter your result in the known column.
Repeat in a different area of the ocean so that you get a different measured
value, again use your formula to calculate and then enter the known temperature.
Click on the straight line button, enter degrees
for the unit of measure and click ok.
Now as you move your cursor over the image the value in the Info box should
be the temperature in degrees celcius.
You can use the plot profile tool to plot the temperature of points
on a line as you move offshore. A line running straight offshore
from the NC Virginia state line will have a plot profile similar to the
one below. The sharp spikes are where the latitude and longitude
lines are (pixel value =0). Note the long distance of cooler water
followed by a rapid shift to warmer water where your line intersects the
gulf stream current followed by cooler water on the other side.
use arrow keys to adjust plot box size
Density Slicing Density Slicing allows you to highlight
a range of values in red. It allows you to pick a range that
you are interested in - say water between 24º and 27 ºC.
Revert to your saved image and gray scale it.
Choose the LUT tool. Then choose density slicing from the options
You can click on the top or bottom of the density slice to increase or
decrease the size of your slice or click in the middle of the slice to
move it up and down the LUT. If all of your calibration is still
included the info window will tell you the upper and lower value of your
Move and size your slice until 24 to 27 degree water is shown in red.
Produce a plot profile of the water temperature going directly south
parallel to the longitude line from from Cape Fear (which is the
point on the coast that sticks out into the ocean just south of Wilmington.
Measure in kilometers how far off shore the warmest part of the gulf
stream is at Cape Fear.
Measure the average temperature of Albemarle Sound. (hint:take separate
measurements on either side of the longitude line and average them)
Produce a density slice map highlighting the water that is between 22 and
24 degrees Celcius.
What do we mean when we say is this a psuedo colored image?
When and why might it be useful to change the color of North Carolina's
land area? Would you choose colors to hide, minimize or highlight
the latitude and longitude lines? Explain the reason for your choice.
Which LUT did you think did the best job of bringing the viewers attention
to the gulf stream pattern? Why?
How do the brightness and contrast adjusters differ in their effects?
Why can't all of North Carolina's outer bank islands be distinguished on
What practical value might these images have for fishermen?
Success will be measured by the following
|Produced required profile plot.
|Accurately measures distance.
| Accurately measures temperature
|Produces required density slice map
of Page Lesson
last update 10/07/99