Panchromatic Sensitive to all or most of the visible spectrum.

Passive system: A system sensing only radiation emitted by the object being viewed or reflected by the object from a source other than the system. See active system.

Photosynthetically active radiation (PAR) Electromagnetic radiation in the part of the spectrum used by plants for photosynthesis.

Photo interpretation: the process of examining aerial photographs and images for the purpose of identifying objects and judging their significance. (NASA Observatorium: Remote Sensing in History)

http://observe.ivv.nasa.gov/nasa/search/index/index.html

Polar orbit: An orbit with an orbital inclination of near 90 degrees where the satellite ground track will cross both polar regions once during each orbit. The term is used to describe the near-polar orbits of spacecraft such as the USA's NOAA/TIROS and Landsat satellites.

Radiation: Energy transfer in the form of electromagnetic waves or particles that release energy when absorbed by an object.

Remote sensing: The technology of acquiring data and information about an object or phenomena by a device that is not in physical contact with it. In other words, remote sensing refers to gathering information about the Earth and its environment from a distance, a critical capability of the Earth Observing System.

For example, spacecraft in low-Earth orbit pass through the outer thermosphere, enabling direct sampling of chemical species there. These samples have been used extensively to develop an understanding of thermospheric properties. Explorer-17, launched in 1963, was the first satellite to return quantitative measurements of gaseous stratification in the thermosphere. However, the mesosphere and lower layers cannot be probed directly in this way--global observations from space require remote sensing from a spacecraft at an altitude well above the mesopause. The formidable technological challenges of atmospheric remote sensing, many of which are now being overcome, have delayed detailed study of the stratosphere and mesosphere by comparison with thermospheric research advances.

Some remote-sensing systems encountered in everyday life include the human eye and brain, and photographic and video cameras.

Resolution: A measure of the ability to separate observable quantities. In the case of imagery, it describes the area represented by each pixel of an image. The smaller the area represented by a pixel, the more accurate and detailed the image. See Digital image

Satellite: A free-flying object that orbits the Earth, another planet, or the sun.

Sensor: Device that produces an output (usually electrical) in response to stimulus such as incident radiation. Sensors aboard satellites obtain information about features and objects on Earth by detecting radiation reflected or emitted in different bands of the electromagnetic spectrum. Analyzing the transmitted data provides valuable scientific information about Earth.

Weather satellites commonly carry radiometers, which measure radiation from snow, ice, clouds, and bodies of water. Spaceborne radars are used for Earth observations, bouncing radar waves off land and ocean surfaces to study sea-surface conditions, ice thickness, and land surface features. A wind scatterometer is a special type of radar designed to measure ocean surface winds indirectly by bouncing signals off the water and measuring them from various angles. Infrared (IR) detectors measure heat generated by Earth features in the IR band of the spectrum.

Photographic reconnaissance sensors in their simplest form are large telescope-camera systems used to view objects on Earth's surface. The bigger the lens, the smaller the object that can be detected. Camera-telescope systems now incorporate all sorts of sophisticated electronics to produce better images, but even these systems need cloudless skies, excellent lighting, and good color contrast between objects and their surroundings to detect objects the size of a basketball. Some of the satellites produce film images that must be returned to Earth, but a more convenient method is to record the image as a series of digital code numbers, then reconstruct the image from the electronic code using a computer at a ground station.

Spectral band: A finite segment of wavelengths in the electromagnetic spectrum. See electromagnetic spectrum

Spectrum: 1. The series of colored bands diffracted and arranged in the order of their respective wave lengths by the passage of white light through a prism or other diffracting medium and shading continuously from red (produced by the longest visible wave) to violet (produced by the shortest visible wave). 2. Any of various arrangements of colored bands or lines, together with invisible components at both ends of the spectrum, similarly formed by light from incandescent gases or other sources of radiant energy, which can be studied by a spectrograph. 3. In radio, the range of wavelengths of radio waves, from 3 centimeters to 30,000 meters, or of frequencies of radio waves, from 10 to 10,000,000 kilocycles. 4. The entire range of radiant energies. See electromagnetic spectrum.

Thematic Mapper (TM): A Landsat multispectral scanner designed to acquire data to categorize the Earth's surface. Particular emphasis was placed on agricultural applications and identification of land use. The scanner continuously scans the surface of the Earth, simultaneously acquiring data in seven spectral channels. Overlaying two or more bands produces a false color image. The ground resolution of the six visible and short wave bands of the Thematic Mapper is 30 meters, and the resolution of the thermal infrared band is 120 meters. Thematic Mappers have been flown on Landsats-4 and -5.

Thermal infrared: Electromagnetic radiation with wavelengths between about 3 and 25 micrometers.

Training Data: Land cover data collected at Land Cover Sample Sites to help identify or label unknown clusters on the unsupervised classification of the TM image and/or to help in the manual interpretation of the TM image. These data can be collected using qualitative or quantitative data collection methods. Training data should never be used to assess the accuracy of the map because they have been used in the training process and you cannot use the same data to train as well as validate your results. GLOBE Program

True-color composite images: These images approximate the range of vision for the human eye, and hence these images appear to be close to what we would expect to see in a normal photograph. True-color images tend to be low in contrast and somewhat hazy in appearance. This is because blue light is more susceptible than other bandwidths to scattering by the atmosphere. Broad-based analysis of underwater features and land cover are representative applications for true-color composites.

http://observe.ivv.nasa.gov/nasa/education/tools/stepby/3bandcombo.html

Unsupervised Clustering: A computer identifies and clusters together pixels in the image that have the most similar spectral properties. The software assigns each cluster an arbitrary color.

Validation Data: Land cover data collected at Land Cover Sample Sites to assess the accuracy of the classified map created using manual interpretation or unsupervised classification of your local TM scene. These data can be collected using qualitative or quantitative data collection methods (quantitative is preferred whenever possible). Collect as many samples as possible for each land cover type present on the map because many samples are needed in the accuracy assessment process. These data should be used only for accuracy assessment. GLOBE Program

Visible: That part of the electromagnetic spectrum to which the human eye is sensitive, between about 0.4 and 0.7 micrometers. See spectrum

Wave: 1. In electricity, a periodic variation of an electric current or voltage. 2. In physics, any of the series of advancing impulses set up by a vibration, pulsation, or disturbance in air or some other medium, as in the transmission of heat, light, sound, etc.

Wavelength: Physical distance of one period (wave repeat).