Target
Object on the terrain of specific interest in a remote sensing investigation.

TDRS
Tracking and Data Relay Satellite

Telemeter
To transmit data by radio or microwave links.

Terrain
Surface of the earth.

Texture
Frequency of change and arrangement of tones on an image.

Thematic Mapper (TM)
A cross-track scanner deployed on Landsat that records seven bands of data from the visible through the thermal IR regions.

Thermal capacity (c )
See heat capacity.

Thermal conductivity (K)
Measure of the rate at which heat will pass through a material, expressed in calories per centimeter per second per degree Centigrade.

Thermal crossover
On a plot of radiant temperature versus time, the point at which temperature curves for two different materials intersect.

Thermal diffusivity (k)
Governs the rate at which temperature changes within a substance, expressed in centimeters squared per second.

Thermal inertia (P)
Measure of the response of a material to temperature changes, expressed in calories per square centimeter per square root of second.

Thermal IR
IR region from 3 to 14 µm that is employed in remote sensing. This spectral region spans the radiant power peak of the earth.

Thermal IR image
Image acquired by a scanner that records radiation within the thermal IR band.

Thermal IR multispectral scanner (TIMS)
Airborne scanner that acquires multispectral images within the 8-to-14mm band of the thermal IR region.

Thermal model
Mathematical expression that relates thermal and other physical properties of a material to its temperature. Models may be used to predict temperature for given properties and conditions.

Thermography
Medical applications of thermal IR images. Images of the body, called thermograms, have been used to detect tumors and monitor blood circulation.

Tie-point
A point on the ground which is common to two images. Several are used in the coregistration of images.

TM
Thematic mapper.

Tone
Each distinguishable shade of gray from white to black on an image.

Topographic inversion
An optical illusion that may occur on images with extensive shades. Ridges appear to be valleys, and valleys appear to be ridges. The illusion is corrected by orienting the image so that the shadows trend from the top margin of the image to the bottom.

Topographic reversal
A geomorphic phenomenon in which topographic lows coincide with structural highs and vice versa. Valleys are eroded on crests of anticlines to cause topographic lows, and synclines form ridge, or topographic highs.

Tracking and Data Relay Satellite (TDRS)
Geostationary satellite used to communicate between ground receiving stations and satellite such as Landsat.

Training area
A sample of the Earth's surface with known properties; the statistics of the imaged data within the area are used to determine decision boundaries in classification.

Trade-off
As a result of changing one factor in a remote sensing system, there are compensating changes elsewhere in the system; such a compensating change is known as a trade-off.

Training site
Area of terrain with known properties or characteristics that is used in supervised classification.

Transmissivity
Property of a material that determines the amount of energy that can pass through the material.

Transparency
Image on a transparent photographic material, normally a positive image.

Transpiration
Expulsion of water vapor and oxygen by vegetation.

Travel time
In radar, the time interval between the generation of a pulse of microwave energy and its return from the terrain.

Tristimulus colour theory
A theory of colour relating all hues to the combined effects of three additive primary colours corresponding to the sensitivities of the three types of cone on the retina.