GEOLOGY422/522 by Scott Hughes, Mary Hodges, & Diana Boyack

Preview the vocabulary and tasks for this module

What is Remote Sensing??? The easiest definition is, "Remote sensing is acquiring data about an object without touching it". This is the quick and easy definition but it could include any type of camera, scanner, radar system, etc. You get the idea. So a better definition might be, "Remote sensing is recording of information from the ultraviolet, visible, infrared and microwave regions of the electromagnetic spectrum (still without touching it), with equipment such as cameras, scanners, lasers, linear arrays. This equipment is located on aircraft or spacecraft, and the analysis of the information obtained is though visual and digital image processing."

So remote sensing is the term we use to describe the: 1 - acquiring of data (usually images of some type), 2 - the processing of that data, and 3 - the interpretation of that data.  This is done by studying the interaction between our object of interest and the electromagnetic spectrum.  Remote sensing in which the object of study is subjected to electomagnetic radiation emitted from the data collection device is active remote sensing.  Radar is an example of active remote sensing.  Passive remote sensing is done by recording the naturally-occurring interaction between the object of study and the source of electromagnetic radiation, such as photography.

Electromagnetic energy has distinctive properties.   The most familiar form of  electromagnetic energy is visible light.  All electromagnetic energy moves at the speed of light (commonly referred to as c = 299,793 km/sec or c = 3 * 10⁸ m/sec in a vacuum), and can be described both as particles and as harmonic waves.  We can describe the movement and  properties of electromagnetic energy in terms of velocity (c), wavelength ( l ), and frequency (v).   For practical purposes, we can consider the speed of light a constant.

The electromagnetic spectrum is the name we give to the continuum of energy that travels through the universe at the speed of light.  In a vacuum, such as interstellar space, electromagnetic energy travels at about 3* 10^8 m/sec, until it hits some matter.  The wavelength of the electromagnetic spectrum varies from nanometers (abbreviation nm, 1 nm = 1/1,000,000,000 meter) to meters.  Matter radiates a range electromagnetic energy.

Velocity and wavelength of electromagnetic energy can change as the energy is propagated through different media (such as air water, solid rock, interstellar space and so on), while frequency remains constant.

Electromagnetic energy that interacts with matter is called incident radiation. The intensity, direction, polarization, wavelength and phase of electromagnetic energy can change when  the energy interacts with matter.  The electromagnetic energy can be transmitted, absorbed, emitted, scattered or reflected from the study object.   The physical properties of the  matter control  what interaction will take place, and how the properties of the electromagnetic energy will be changed.

Force fields include things like gravity, and magnetic fields .

To learn more about "Remote Sensing" you can visit the following websites for more information. It's not required though and some of the tutorials are very long and in depth. Use for reference in understanding terms. The Remote Sensing Tutorial: This is one of the best tutorials for more indepth information on Remote Sensing by NASA. Canada Centre for Remote Sensing: This is a good place for more simplified definitions and teacher resources. Fundamentals of Remote Sensing and Image Analysis: This is a web page with links to many other Remote Sensing sites. NASA's Observatorium: NASA's public access site for Earth and Space data. Images and educators resources. Cartography and Remote Sensing : A USGS site about "Cartography, Geologic Mapping, & Photogrammetry". Geographic Information Systems - GIS: another good USGS site to learn more about GIS. Remote Sensing Slide Show Remote Sensing Using Satellites Singapore Science Center: Principles of Remote Sensing

Remote Sensing Methods

Aerial Photography
Modern, technology-based remote sensing began with photography.  As transportation technology advanced, photography of more and more distant objects became feasible.  At the same time, the need for correction of distortion from camera lenses, and accurate measurement of the surfaces represented in photographs became important.  Photography and the ability to translate the information contained in photographs into accurate measurements of phenomena on planetary surfaces, combined with traditional cartography, are the basis of Geographic Information Systems.  Visit Geographic Information Systems - GIS from the United States Geological Survey to learn more about GIS.

Remote sensing photography uses visible, infrared, and ultraviolet light.   Because aerial photography is done from an unfamiliar viewpoint (straight down) and at a large distance, understanding aerial photographs requires special techniques and a certain amount of practice.  If the photographs record wavelengths other than visible light, even more complexity results.  Air photos are not absolutely accurate representations of the ground they depict, and must be processed to correct for distortion. An aerial photograph that has been corrected is called an orthophoto.  

Visual information in a photograph is in analog form. The only spot on the photograph that is an exact representation of the surface is the pixel straight down from the camera and in the center of the camera's focus. The first step in producing an image useful in GIS is to digitize and correct the photograph.  The analog information of hue, brightness and contrast is changed into digital information on a computer.  Then the digital image is manipulated as if it were a rubber sheet to correct for distortion due to the shape of the camera lense, the angle that the photograph was taken, and any other distorting factors.  Eventually, an image is produced that can be "ground truthed," which is exactly what it sounds like.  The information is matched to the topographic map of the area, and a trained person goes out and looks to see if the orthophoto image conforms to reality.

Spectroscopy

Spectroscopy studies radiation given off by planets, stars and other celestial objects.  The spectrum of radiation emitted by an object can be analyzed and the data obtained from such analysis yields information on the composition of the radiating object and the medium through which the radiation passes.  Visit Explore the Universe with ORFEUS-SPAS II, the Space Sciences Directorate, and the LABORATORY FOR ASTRONOMY AND SOLAR PHYSICS, to learn more about these spectroscopy and its related disciplines.

Magnetic and gravity anomalies

The study of variations in the strength of gravitational and magnetic fields is part of geophysics, but can be considered as remote sensing, especially in the investigation of extraterrestrial bodies. 
The IMAGE / POETRY K12 Space Science Site ,the  Cosmic and Heliospheric Learning Center,and The Exploration of the Earth's Magnetosphere\" from Goddard Space Flight Center are sites to visit to learn more about gravity and magnetic studies.  For even more, go to http://www.nasa.gov and use their search engine to find sites with information about these geophysical methods, the equipment and missions that use them and the data collected in these studies.

GIS

• DRG Digital Raster Graphics
• GLIS glossary

Visible Earth by NASA is a searchable directory of images, visualizations, and animations of the earth. Fun site to just look through - - http://visibleearth.nasa.gov/

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