T: Standard abbreviation for absolute temperature (see Kelvin).
Table digitiser: Equipment used to digitise vector data co-ordinates.
Talbot: Photometric unit equivalent to 1 lm sec.
Target: (1) An object on the terrain of specific interest in a remote
sensing investigation. (2) The portion of the Earth's surface that produces,
by reflection or emission, the radiation measured by the remote sensing
system.
Telemetry: The science of measuring a quantity or quantities, transmitting
the measured value to a distant station, and there interpreting, indicating,
or recording the quantities measured.
Temporal resolution: Repeat cycle or interval between successive
image acquisitions for a given area.
Tera: Standard prefix indicating 10^12.
Texture: In a photo-image, the frequency of change and arrangement
of tones. Some descriptive adjectives for textures are fine, medium or coarse,
and stippled or mottled.
Texture transformation: An image processing technique which computes
the average standard deviation within a filter region around each pixel.
This transformation is useful to highlight differences in the texture of
image features.
Thematic map: A map designed to illustrate a particular theme.
Thematic mapper (TM): An imaging device carried by the later Landsat
satellites which records scenes in seven wavebands, six in the visible and
reflective infrared, with a resolution of 30 m, and one in the thermal infrared
with a resolution of 120 m.
Theme: A simple method for categorising multi-channel image data
by defining minimum and maximum values in each channel. Themes may be used
to broadly define image features for classification or segmentation purposes.
Theme mapping: Process of painting image pixels which satisfy a pre-defined
spectral theme as a particular colour.
Thermal inertia: A measure of the response of a material to temperature
changes, expressed in cal cm^-2 °C^-1 S^-0.5.
Thermal infrared: The preferred term for the mid-range wavelengths
of the infrared region, extending roughly from 3 µm at the end of
the near infrared, to about 15 or 20 µm, where the far infrared begins.
In practice the limits represent the envelope of energy emitted by the Earth
behaving as a grey body with a surface temperature around 300K (approximately
27°C).
Threshold: The limit in terms of image values beyond which processing
is not performed.
Tie point: A point on the ground which is common to two images. Such
points are used to co-register multi-source imagery. See also ground
control point.
TIMS: Thermal Infrared Multi-spectral Scanner.
TIR: Thermal infrared.
TIROS: Television infrared Observation Satellite; polar-orbiting,
US meteorological satellite prior to the NOAA series.
TM: Thematic Mapper.
Tone: Each distinguishable shade variation from black to white.
Total field of view (TFOV): The overall plane angle or linear ground
distance covered by a multi-spectral scanner in the across-track direction,
transverse to the direction of travel of the sensor platform.
Total power law: Incident radiation on a body is either transmitted,
absorbed or reflected so that the ratios of each of transmission, absorption
and reflection to the total incident power (F) must sum to 1 (that is, t
+ a + r = 1).
TOVS: TIROS Operational Vertical Sounder; atmospheric sounding instrument
carried on TIROS and NOAA satellites, comprising HIRS, MSU and SSU.
Trackball: An interactive control for inputting spatial data to a
computer or selecting a screen option.
Training: Informing the computer system which sites to analyse for
spectral properties or signatures of specific land cover classes; also called
signature extraction.
Training patch: A spatially defined area in an image (usually fairly
uniform in appearance and description) which is used to define class seed
values.
Training region: An image or a group of images which is used to develop
a classification.
Training theme: A theme (in which the maximum and minimum values
of specified channels are defined) which is used in the training region
to develop class seed values.
Transformation: An image processing technique which modifies pixel
values in one or more channels of an image.
Transmission: The amount of radiation of different wavelengths that
a filter, lens, or film will transmit or allow to pass through without change.
Transmissivity: Transmittance for a unit thickness sample. One may
further qualify it as spectral transmissivity.
Transmittance (t): The ratio of the radiant flux transmitted through
a body to that incident upon it.
Transparency: (1) The light-transmitting capability of a material.
The loss of light in transmission through good optical glass. Approximately
2.4% of visual light is lost for every centimetre of glass traversed. (2)
A positive image upon glass or film, intended to be viewed by transmitted
light, either black and white or in colour; also called a diapositive.
Trichromatic: Three-coloured. In computer graphics, trichromatic
generally refers to the three additive primary colours (blue, green and
red) which combine to create all others.
Tristimulus values: Relative amounts of the three additive primary
colours (blue, green and red) that are combined to create any other colour.
True-colour film: A term to differentiate ordinary colour film from
false-colour near infrared film. Colours recorded on true colour film should
be truthful reproductions of those in the original scene.