Images acquired by satellites have been used to produce local, regional, national, and global composite multispectral mosaics. They have been used in countless applications including monitoring timber losses in the U.S.
Pacific Northwest, establishing urban growth, and measuring forest cover.
Remote sensing images have also been used in military operations, to locate mineral deposits, to monitor strip mining, and to assess natural changes due to fires and insect infestations.
Data Collection in General
Thinking about remote sensing in a most general sense, we can easily distin- guish types of data collection by the platform and by sensor technology. If
the remote sensing is based on satellite images or data, in most cases we are likely to have multispectral, hyperspectral, or radar images or data. If it is air- plane-based, then we are more likely to have aerial photography, multispectral, or LiDAR images or data. If it is ground-based, then we are most likely to find photography, multispectral, or LiDAR images and data.
These rules of thumb have exceptions, of course, and will change as certain types of sensor technology and remote sensing systems become cheaper.
They are simply helpful in seeing the relationship between costs, types of data, and application types. Applications in smaller areas tend to use air- plane-based or ground-based sensor technologies; larger areas tend toward satellite-based remote sensing.
Coastal Monitoring
An important application area is coastal monitoring. Because of the key role of dynamic processes in coastal erosion, coastal monitoring applications tend to use remote sensing sources that can repeat their observations often.
Aerial and LiDAR photography and data may be suitable for smaller areas if the area is generally cloud-free; multispectral satellite images and data may be useful for larger areas, and radar may be used for large areas, or areas with frequent cloud cover.
Global Change
With an increase in average temperatures worldwide, shrinking glaciers, and shrinking ice packs, the study of changes to glaciers and Arctic and Antarctic ice fields has benefited greatly from the use of remote sensing images and data. The frequency of observations helps scientists keep track of changes to ice fields and even icebergs in the water. Detailed observations, combined with measurements on the ground, help researchers monitor minute
Multispectral sensors produce data and imagery to help monitor and model complex coastal changes.
Fromhttp://earthasart.gsfc.nasa.gov/images/
netherla_hires.jpg
changes in ice fields. Made available online to other researchers, these mea- surements, images, and data have become a crucial part of a key area of global change research.
Urban Dynamics
Because of the frequency of observation, satellite-based remote sensing images and data have proven to be very useful in documenting and assessing the growth of large cities around the world and distinguishing changes and processes. Urban dynamics are complex, but individual changes in a single area can be compared to assess the impacts of various policies and urban planning programs. Data and models developed to understand past growth can be used to make predictions of future growth and to assess alternative policy and planning proposals.
Precision Farming
Detailed remote sensing images and data, from a variety of platforms, are used by farmers to reduce the use of and become more efficient in the appli- A composite of different multispectral data to produce a “ picture-like” image of the world.
Fromhttp://earthobservatory.nasa.gov/Newsroom/BlueMarble/
cation of fertilizers and pesticides. Agricultural factors including plant health, plant cover, and soil moisture can be monitored with remote sensing data (see Plate 5). By combining the remote sensing images and data from different sources, deficiencies of one remote sensing system can be made up.
For instance, Landsat provides multispectral data on average only once every 16 days for any place in the continental United States and is impaired by cloud coverage, even partially cloudy weather. By using radar data, scien- tists have been able to help farmers keep track of changing soil and plant conditions more frequently, which is especially critical during particular phases of plant growth (e.g., pollination).
Summary
Remote sensing is the collection of data without directly measuring the object. It relies on the ref lectance of natural or emitted electromagnetic radiation (EMR). It has become an important and, in some applications, key means of data collection. The many types of remote sensors can be basically distinguished into two groups. Passive sensors rely on natural EMR; active sensors require an additional source of EMR. Remote sensing involves the complicated calibration of spectral signatures indicative of things or events with various characteristics and capabilities of sensors. Most sensors distin- guish the EMR they detect as bands, which refers to specific ranges of EMR a sensor detects. Sensors also distinguish between spatial, temporal, and spec- tral resolutions. The many applications using remote sensing keep growing.
Aerial imagery (here from a digitized aerial photograph) can show a great amount of detail.
Increasingly, remote sensing has been making inroads into traditional sur- veying domains.
Review Questions
1. What does the term LiDAR stand for?
2. What does the term panchromatic mean?
3. Data from remote sensing is a powerful tool for analysis. What has prevented it from being more widely taken advantage of?
4. What is the oldest commercial satellite system that is still in use?
5. What is the size/scale of geographic area most well-suited to being studied using remote sensing data? Small, medium, or large?
6. What remote sensing technology is being used in modern surveying?
7. What were some early applications for radar-based remote sensing?
8. What is the highest resolution of panchromatic remote sensing data now available?
9. When was remote sensing first used?
10. How is remote sensing data usually stored?
Answers
1. What does the term LiDAR stand for?
LiDAR stands for Light Detection and Ranging.
2. What does the term panchromatic mean?
Panchromatic is a descriptive for all wavelengths of the visible spectrum.
3. Data from remote sensing is a powerful tool for analysis. What has prevented it from being more widely taken advantage of?
Remote sensing data is costly to produce.
4. What is the oldest commercial satellite system that is still in use?
The oldest commercial satellite system is called “Landsat.” The first satellite of this system was launched in July 1972.
5. What is the size/scale of geographic area most well-suited to being studied using remote sensing data? Small, medium, or large?
Generally, remote sensing data is most useful for studying large areas.
6. What remote sensing technology is being used in modern surveying?
Surveying now uses laser sensors for accurately measuring distances.
7. What were some early applications for radar-based remote sensing?
Some of the first applications for radar-based remote sensing were climate analysis, iceberg detection, and geology.
8. What is the highest resolution panchromatic remote sensing now available?
The highest generally available resolution is less than 1 m for panchromatic remote sensing data.
9. When was remote sensing first used?
Most people consider the use of the telescope in the 17th century to be the first use of remote sensing.
10. How is remote sensing data usually stored?
Remote sensing data is usually stored on computer using a raster format.
Chapter Readings
Conway, E. D. (1997). An Introduction to Satellite Image Interpretation. Baltimore: Johns Hopkins University Press.
Gibson, P. J. (2000). Introductory Remote Sensing: Principles and Concepts. New York:
Routledge.
Lillesand, T. M., R. W. Kiefer, & J. W. Chipman. (2004). Remote Sensing and Image Interpretation (5th ed.). New York: Wiley.
Sabins, F. F. (1997). Remote Sensing: Principles and Interpretation (3rd ed.). New York:
Freeman.
Web Resources
One of the most consumer-friendly remote sensing-based web applications (registra- tion required for full access) is available online at www.keyhole.com/
For information about LandSat 7, see the website www.keyhole.com/
NASA provides many fascinating images at its website at http://visibleearth.nasa.gov/
Documentation of wetland destruction using animations is available online at http://
svs.gsfc.nasa.gov/vis/a000000/a002200/a002210/index.html
For in-depth discussion of everything related to remote sensing, with an emphasis on Landsat, but covering other sensor technologies in great detail, see http://rst.gsfc.
nasa.gov/
For information about SPOT satellites, see www.spot.com/html/SICORP/_401_.php Another source for information about Landsat satellites is available online at http://
landsat.gsfc.nasa.gov/
For an excellent interactive tutorial about various aspects of remote sensing, see http://satftp.soest.hawaii.edu/space/hawaii/
A tutorial introduction to LiDAR is available online at www.ghcc.msfc.nasa.gov/sparcle/
sparcle_tutorial.html
Download Landsat data online at www.earthexplorer.usgs.gov
Exercises
1. Uses of Remote Sensing
Based on the discussion in the textbook and lecture presentation, determine with your neighbor three remote sensing applications and the data required for each.
What is the spectral, the temporal, and the spatial resolution that each application requires?
2. Remote Sensing Laboratory Exercise Objectives
To better understand the use and types of remote sensing.
Overview
For your first employment following completion of your undergraduate degree you can choose between helping a company set up a remote sensing service for urban areas wanting quick information about changes in their areas and helping its sister company provide the same service for national parks in the United States. Choose one of the positions and then to make an assessment of the remote sensing data that is available for that service.
You are one of many people preparing a description of a new service. The man- agement will review the descriptions and decide which services it will develop fur- ther.
Instructions
This is an important first step for either service and you have to be sure that your assessment is well documented. Your assignment is to prepare a one-page (single- spaced) assessment of the type of service you propose the company will provide using this set of topics as an outline.
1. Describe the service, including the remote sensing systems.
2. Explain the service in terms of the problem or issue you find requires this service.
3. Identify the data requirements (resolution and frequency).
4. Discuss the role of resolution (spectral, spatial, and temporal) in your study.
5. Identify any additional data the service will need.
6. Explain how this service can be developed into other services.