Thermal infrared imagery
Remote sensing of temperature uses the amount of radiation reflected or emitted in the thermal infrared portion of the electromagnetic spectrum. The thermal infrared range of the EMS is generally considered to be between 3 and 14 µm. Due to absorbtion by atmospheric water in some portions of the EMS, wavelengths for measuring thermal infrared radiation are generally considered to be from 3-5 µm and 8-14 µm. A number of factors affect the amount of thermal infrared radiation reflected or emitted from the land surface. These include:
Remotely-sensed surface temperature data are commonly used in studies of water temperature or ocean current flows. Surface temperature, however, also has applications to terrestrial land management, and has been used in conjunction with spectral vegetation indices to assess rangeland cover and change. Surface temperature data are also a key input into the biophysical models used to estimate attributes like evapotranspiration or net primary productivity.
Thermal anomalies representing events like active fires are created from thermal infrared or surface temperature images.
Output is an image layer/dataset with values representing either emissivity of thermal infrared radiation or surface temperature.
In most cases, surface temperature will be an input to another remote sensing product that produces information more directly related to rangeland management. One limitation to remotely-sensed surface temperature measurements is that the values recorded by the sensor are a combination of soil surface and vegetation temperature. This is problematic when used as inputs to biophysical models because most models need temperature of the vegetation only.
Surface temperature is calculated from the thermal infrared radiance values recorded by a sensor. These readings are calibrated to surface temperature.
For the most part, existing or standard-product surface temperature datasets are used rather than calculating new surface temperature datasets manually from raw imagery.
Image from N.M. Short's Remote Sensing Tutorial http://landsat.gsfc.nasa.gov/education/tutorials.html
Thermal infrared images from southern California showing the difference in temperature at different times of day.
Comparison of a false-color composite Landsat ETM+ image (left) and the Landsat ETM+ thermal band (right) for a portion of southern Idaho near Craters of the Moon National Monument.
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