Glossary - R

Tools| A| B| C| D| E| F| G| H| I| J| K| L| M| N| O| P| Q| R| S| T| U| V| W| X| Y| Z| All

Radar - "Short for ""radio detection and ranging,"" radar sends out short pulses of microwave energy and records the returned signal's strength and time of arrival."

Radiometer - A device that detects and measures electromagnetic radiation.

Radiometeric - Relating to, using, or measured by a radiometer. The measurement of radiation.

Raster Data - An abstraction of the real world where spatial data is expressed as a matrix of cells or pixels, with spatial position implicit in the ordering of the pixels. With the raster data model, spatial data is not continuous but divided into discrete units. This makes raster data particularly suitable for certain types of spatial operations (e.g., overlays or area calculations). Unlike vector data, there are no implicit topological relationships.

Raster Graphics - Graphics in which an image is generated by scanning an entire screen or page and marking every point as black, white, or another color (as opposed to vector graphics).

Rasterize - The process of converting vector points, lines, and areas into raster image format.

Raw Data - Numerical values representing the direct observations output by a measuring instrument transmitted as a bit stream in the order they were obtained.

Real-time - Time in which reporting on events or recording of events is simultaneous with the events. For example, the real time of a satellite is the time in which it simultaneously reports its environment as it encounters it.

Remote Sensing - (1) In the broadest sense, the measurement or acquisition of information about some property of an object or phenomenon, by a recording device that is not in physical or intimate contact with the object or phenomenon under study. (2) Instruments that record characteristics of objects at a distance, sometimes forming an image by gathering, focusing, and recording reflected light from the Sun, or reflected radio waves emitted by the spacecraft.

Resampling - Modifying the geometry of an image (which may be from either a remotely sensed or map data source). This process usually involves rectification and/or registration.

Resolution - (1) A measure of the amount of detail that can be seen in an image; the size of the smallest object recognizable using the detector. (2) Intensity or rate of data sampling. In remotely sensed imagery, resolution is significant in four measurement dimensions: spectral, spatial, radiometric and temporal.

Retrograde - (1) Of or relating to the orbital revolution or axial rotation of a planetary or other celestial body that moves clockwise from east to west, in the direction opposite to most celestial bodies. (2) Of or relating to the brief, regularly occurring, apparently backward movement of a planetary body in its orbit as viewed against the fixed stars, caused by the differing orbital velocities of Earth and the body observed.

Revolution - Orbital motion about a point located outside the orbiting body.

Rotation - Motion around an axis passing through the rotating body.

Row - (1) The latitudinal (nominal) center line of a Landsat scene. (2) The scan lines that constitute an image.