Thermal Infrared Remote Sensing

Introduction All previous sensor systems discussed sensing or measuring reflected solar radiation In the thermal infrared we measure emitted terrestrial radiation –Energy is first absorbed, then is emitted by the object Emitted Absorption Reflected

Comparison of Reflective and Thermal Bands Landsat 7 ETM+ data

Day and Night Thermal Images Lillesand & Kiefer

The level of radiation emitted by objects is determined by their temperature emissivity Absorption, not scattering, is the dominant atmospheric effect

Temperature Concentration of internal thermal energy –is a measure of the average kinetic energy of atomic and molecular motions within bodies above absolute zero (0 degrees Kelvin) Interactions (collisions) among these units lead to changes in energy --- emitted as radiation that can be detected externally.

Thermal Energy of an Object is Indicated by its: Kinetic Temperature –is measured by a thermometer –also called internal, real, contact and thermodynamic temperature Radiant Temperature –is measured by a radiometer –also called external, apparent and non- contact temperature

Relation between Kinetic and Radiant Temperatures If the emissivity of an object is 1 (i.e., a perfect blackbody), then its kinetic temperature equals its radiant temperature But, for natural or graybodies, the kinetic and radiant temperatures differ according to the emissivity of the body

Radiant temperature -- the quantity measured by remote sensors -- can be derived from the Stefan-Boltzman law T rad =    1/4 T kin Emissivity (  ) controls the radiant temperature of an object two objects with the same kinetic temperatures, but different emissivities will have different radiant temperatures

Summary of Basic Thermal Properties Temperature of an object measured remotely is known as its radiant or apparent temperature Radiant temperature is the blackbody or kinetic temperature reduced by its emissivity Remotely sensed thermal IR radiances are a composite of emitted energy, emissivity, and atmospheric and sensor effects

Time of day is critical to assessing temperature response patterns Diurnal Variation in Radiant Temperatures NoonDawnSunset Radiant Temperature Avery & Berlin, 1992

Reflective Bands Death Valley, Nevada Thermal Infrared Bands

Thermal IR image of Lake Tahoe over Landsat TM image

Thermal and Visible Images of Glen Canyon and Surrounding Sandstone

Urban Heat Island Effects Surface Temperature Feb. 27, K 251K MUSA Boundary St. Paul Minneapolis

St. Paul Urban Heat Island Effects Surface Temperature July 16, K 251K MUSA Boundary

Day (left) and night (right) thermal images of a power plant with plume of hot water coming into river An example of density slicing Lillesand & Kieffer

Detection of Building Heat Loss Remote Sensing Tutorial

Fire Detection

Atlantic Gulf Stream Temperatures temperature range, 5 – 25 C

Global Sea Surface Temperature