Electromagnetic Radiance (EMR)
EMR – Energy emitted by the objects of
which absolute temperature is above zero.
The magnitude and spectral range of the
emitted EMR are governed by the
Review of Radiation Laws
All objects at temperature above absolute 0oK emit (273.59oC, -459.67oF)
Stefan-Boltzmann law: W = T4
W-total emitted radiation
T-temperature in oK
The total emitted radiation from a blackbody is
proportional to the fourth power of its absolute
► Wien's displacement law: = 2,897.8/T
-peak wavelength, T-temperature in oK
► As temperature of objects increases, the
wavelength of peak emittance becomes shorter
► Emissivity: e = M/Mb
M-emittance of a given object
Mb-emittance of blackbody
e = 1 (blackbody)
e = 0 (whitebody, perfect reflector)
► The ratio between the emittance of a given
object and that of blackbody at the same
Emissivity of Common Materials
Clear water 0.98-0.99
Wet snow 0.98-0.99
Human skin 0.97-0.99
Rough ice 0.97-0.98
Asphalt concrete 0.94-0.97
Basalt rock 0.92-0.96
Dry mineral soil 0.92-0.94
Dry vegetation 0.88-0.94
Granite rock 0.83-0.87
Sheet iron (rusted) 0.63-0.70
Polished metals 0.16-0.21
Aluminum foil 0.03-0.07
Highly polished gold 0.02-0.03
Water, Ice and Snow
Water, ice, and snow generally have a high emissivity, 0.94 to 0.99, across
the thermal infrared region.
Snow is unusual in that it has a high reflectance in the solar (visible)
region where most of the downwelling energy is during the day, and a
very high emissivity in the thermal region.
Soil and Minerals
Soil, rocks, and Minerals show strong spectral
features between 8 and 10 microns that depend on
the grain size.
Soil signature in the 3 to 5μm region depends on the
water and organic content. The dryer, purer soils
have lower emissivities in this region.
Green vegetation typically has a very high emissivity because
it contains water.
Senescent (dry) vegetation has a more variable emissivity,
especially in the 3 to 5μm region, which depends on the type
and structure of the cover type, the dryness, etc.
Manmade materials such as polished metals have among
the lowest emissivity values, can be made less than 0.01
(better than 99% reflecting).
“Rocky” materials such as asphalt and brick are high and
range from 0.90 to 0.98
TIROS (Television IR Operational Satellite), launched in 1960
GOES (Geostationary Operational Environmental Satellite), TIR
at 8km spatial resolution, full-disk of Earth, day and night
HCMM (Heat Capacity Mapping Mission), launched in 1978600m spatial resolution, 10.5 – 12.6 micron range
CZCS (Coastal Zone Color Scanner) on Nimbus 7, launched in
1978, for SST (sea surface temperature).
AVHRR (Advanced Very High Resolution Radiometer), 1.1 and 4
km TIR bands
TIMS (Thermal Infrared Multispectral Scanner), Airborne, 6
ATLAS (Airborne Terrestrial Applications Sensor), 15 bands
Landsat 4,5,7; Band 6- 10.4 – 12.5 m, 120 m (4,5), 60 m (7).
ASTER (Advanced Spaceborne Thermal Emission and Reflection
Radiometer) on Terra, 5 bands 8.125-11.65 micron range (14
Surface temperature detection
Fire detection and fire risk mapping
Evapotranspiration and drought monitoring
Estimating air temperature
Oil spill monitoring
Water quality monitoring
Volcanic activity monitoring
Urban heat island analysis