GEOG 160
Mapping Our Changing World

7.9 Glossary


Remote sensing: Data collected from a distance without visiting or interacting with the phenomena of interest.

Space-borne remote sensing: The use of sensors attached to satellite systems continually orbiting around the Earth.

Aerial imaging systems: Sensors attached to aircraft and flown on demand, meaning that their data capture is not continuous.

Sensors: Instruments for capturing electromagnetic energy emitted and reflected by objects on the Earth's surface.

Electromagnetic radiation: A form of energy emitted by all matter above absolute zero temperature (0 Kelvin or -273° Celsius).

Electromagnetic spectrum: Relative amounts of electromagnetic energy emitted by the Sun and the Earth across the range of wavelengths.

Visible wavelengths: The peak wavelengths of electromagnetic spectrum which humans can see.

Atmospheric window: Areas of the electromagnetic spectrum which are not strongly influenced by absorption.

Transmissivity: The ability of a wavelength to pass through these atmospheric windows.

Image Interpretation Elements: A set of nine visual cues that are used to interpret imagery. Those elements are: size, shape, color/tone, pattern, shadow, texture, association, height, and site.

Spectral Response Pattern (spectral signature): The magnitude of energy that an object reflects or emits across a range of wavelengths.

Normalized Difference Vegetation Index: Mathematical formula for calculating the “greenness” in a scene using Near-Infrared and Red bands from an image.

Spatial Resolution: Refers to the coarseness or fineness of a raster grid.

Spectral Resolution: The ability of a sensor to detect small differences in wavelength.

Radiometric Resolution: The measure of a sensor's ability to discriminate small differences in the magnitude of radiation within the ground area that corresponds to a single raster cell.

Temporal Resolution: Describes the amount of time it takes for a sensor to revisit a given location at the same viewing angle during its orbit.

Geometric Correction: Is applied to satellite imagery to remove terrain related distortion and Earth movement based on a limited set of information.

Radiometric Correction: Techniques for removing noise from imagery, including Earth-sun distance corrections, sun elevation corrections, and corrections for atmospheric haze.

Mosaic: Adjoining neighboring images together in a way that preserves their geographic relationship.

Land cover: The kinds of vegetation that blanket the Earth's surface, or the kinds of materials that form the surface where vegetation is absent.

Land use: The functional roles that the land plays in human economic activities (Campbell, 1983).

Maximum likelihood classification: One of the most commonly used algorithms computes the statistical probability that each pixel belongs to each class. Pixels are then assigned to the class associated with the highest probability.

Sun synchronous polar orbit: Orbital path that circles the Earth 640 km above the surface, from pole to pole, crossing the equator at the same time every day.

Geosynchronous orbit: Orbital path common to communications and some weather satellites that remain over the same point on the Earth's surface at all times.

Instantaneous Field of View: The ground area covered by a single pixel.

Passive remote sensors: Only measure radiation emitted by other objects (IKONOS, Landsat, AVHRR).

Active remote sensors: Transmit pulses of long wave radiation, then measure the intensity and travel time of those pulses after they are reflected back to space from the Earth's surface (JERS, ERS, Radarsat).

Imaging Radar: Active remote sensor system that record pulse intensity or the round-trip distance traveled by pulses reflected back to the sensor.

Georeference: Define the images existence in a physical space, establishing a location in terms of map projection and coordinate system.

Orthoimage: A georeferenced image prepared from an aerial photograph or other remotely sensed data ... [that] has the same metric properties as a map and has a uniform scale.

Orthorectification: The process of creating an orthoimage from an ordinary aerial image.

Photogrammetry: Profession concerned with producing precise measurements of objects from photographs and photoimagery.

Optical Axis: A straight line between the center of a lens and the center of a visible scene.

Vertical Aerial Photograph: Is a picture of the Earth's surface taken from above with a camera oriented such that its optical axis is vertical.

Perspective View: All light rays reflected from the Earth's surface pass through a single point at the center of the camera lens.

Planimetric View: Looks as though every position on the ground is being viewed from directly above.

Relief Displacement: Objects at positions lower than the mean elevation of the surface will be displaced toward the principal point.

Rectification: Process by which distorted perspective views can be transformed into plan views.

Stereoscopic: Viewing your environment simultaneously from two slightly different perspectives enables you to estimate very accurately which objects in your visual field are nearer, and which are farther away.

Parallactic Angle: The intersection of your two optical axes at the object form when you fix your gaze upon an object.

Stereopair: A pair of overlapping vertical aerial images.

Stereoplotter: Instruments to trace, or compile, the data shown on topographic maps from stereoscopic images.

Anaglyph Image: Images contain two differently filtered colored images, one for each eye, to create a 3 dimensional viewing perspective.

Digital Orthophoto Quad (DOQ): Raster images of rectified aerial photographs.