Thermal Imagery

Name the 5 parts of the IR spectrum

• NIR: .75-1.4 um

• SWIR: 1.4-3

• MWIR: 3-8 um

• LWIR: 8-15

• FIR: 15-1000um

Kirchoffs law of thermal radiation

• At thermal equilibrium, emissivity of surface/body equals absorptivity

Black Body Radiation Concept

Black body (idealized) that absorbs all light frequencies falling onto it (no light reflected or transmitted)

Wein's Displacement law

• Relationship between temperature of black body and WL emitting radiation most intensely

• Higher temperature correlates with amount of radiated energy, and peak radiation curve moves to shorter WL

Thermal detectors (and 3 kinds)

• Formed from exotic materials sensitive to thermal region, needs cooling to low temps with N/He to maintain sensitivity

• InSb (Indium Antimonide): mid-IR around 5um

• Ge:Hg (Germanium-Mercury): Far IR around 10um

• MCT (mercury cadmium telluride): 8-14 um

Thermal Radiometer

• Lens/Mirror gathering ground radiation, then focuses on detector

• Specific field of view via field stop, and filters to restrict WL

• Specific to WL and field of view

What is a Chopper

• Part of Thermal Radiometer that interrupts radiation reaching detector

  • As it rotates, radiation is detected

Thermal Scanners

Energy collected by scanning mirror first focused onto parabolic mirror, then flat stationary mirror to focus energy on IR sensor

Roll Correction Unit

Sends signal permitting electric control unit to correct signal to reduce geometric error via aircraft stability

Small IFOV

• Geometric error where less energy reaching the detector, radiance measurements less reliable

• Pixel size usually bigger

Tangential scale distortion

• At nadir, sensor closer to ground than edges, distance differences lead to geometric error compressing features along axis perpendicular to flight line

• Images near flight line more circular, away are more ovals

• Not same as relief distortion

Why does material brightness vary with day and night temp

Specific heat

Thermal inertia

• Ability to resist change in temp (measures how slow/quick objects change temp)

Heat capacity mapping mission (HCMM)

• Experimental satellite lasting 2 years

• sun-synchronous measuring temp differences at Earth's surface at different points in daily heating/cooling cycle

• Soil moisture and plant canopy temps, UHI and geothermal surfaces, mapping thermal properties of rocks and minerals

Name satellites with thermal sensors (7)

• Landsat

• modis

• aster

• sentinel-3

• viirs

• goes

• smap