| ES 771 Lecture
James S. Aber |
INTRODUCTION TO REMOTE SENSING
Remote sensing is the science and art of gathering information about an object from a distance. In other words, measurements or observations are taken without making direct physical contact with the object in question. For this course, the focus will be on remote sensing of the Earth's surface from above--aerial or space vantages. The electromagnetic spectrum is the energy that carries information through the atmosphere from the Earth's surface to the sensing device (see RSE fig. 2-7).
Taken from EROS Data Center--glossary.
Passive methods, such as photography and multispectral scanning, gather the ambient energy available. Active systems, namely radar, supply their own energy to illuminate the scene. Attributes of "ideal" and "actual" remote sensing are summarized below based on Lillesand and Kiefer (1994).
Ideal Remote Sensing
- Uniform energy source: Constant energy over all wavelengths at known output, irrespective of time and place.
- Neutral atmosphere: Noninterfering atmosphere that would neither absorb nor scatter electromagnetic energy.
- Unique spectral signatures: Each object would have a unique and known spectral response everywhere on Earth's surface (see RSE fig. 2-17).
- Super sensor: Sensing system that would be highly sensitive through all wavelengths of interest and would be economical and practical to operate.
- Real-time data handling: System that allowed instant processing of data and presentation of images.
- Multiple data users: Remotely sensed data would be useful to scientists and managers from all disciplines; one data set could supply needs of all potential users.
Actual Remote Sensing
- Energy source: Varies with time, place, and objects in ways that cannot be fully predicted. Calibration is sometimes possible, but the exact nature of available electromagnetic energy is usually not known.
- Atmosphere: Varies according to latitude, season, time of day, local weather, etc. Strong absorption and scattering are the rule at most times and places (see RSE figs. 2-15 & 2-20).
- Spectral signatures: All objects have theoretically unique signatures, but in practice these may change and cannot always be distinguished; many objects appear the same.
- Real sensors: No existing sensing system can operate in all wavelengths of interest. Each system is limited by its optical or electronic nature to certain wavelengths (see RSE table 1-3). Likewise certain systems are limited by their high cost of operation.
- Data handling: Many systems now generate far more data than can be handled by either visual inspection or computer analysis. NASA's Earth Observing System (EOS) will greatly exacerbate this problem. Few systems operate with real-time imagery.
- Multiple users: No single combination of remote sensing data and analysis will satisfy all users. Many users are not knowledgeable about subjects outside their immediate disciplines and thus cannot appreciate the full potential or limitations of remotely sensed data and images.
Reference
- Lillesand, T.M. and Kiefer, R.W. 1994. Remote sensing and image interpretation. J. Wiley & Sons, New York, 750 p.
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© Notice: ES 771 is presented for the use and benefit of students enrolled at Emporia State University. Any other use of text, imagery or curriculum materials is prohibited without permission of the instructor. Last update 2006.