Glossary

Radiance

The amount of light directly detected by remote sensing instruments. 

Radiometer

 A device that detects and measures electromagnetic radiation.

Radiometric

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.

Raw data

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

Real time

The 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.

Reflectance

The measure of the proportion of light or other radiation striking a surface which is reflected off it.

Remote sensing

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.

Remote sensing instruments 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

A measure of the amount of detail that can be seen in an image; i.e. the size of the smallest object recognisable using the detector.

In remotely sensed imagery, resolution is significant in four measurement dimensions: spectral, spatial, radiometric and temporal.