EM 1110-2-2907
1 October 2003
Reflected
Emitted
Absorbed
Transmitted
Figure 2-17. Radiation striking a target is reflected, ab-
sorbed, or transmitted through the medium. Radiation is
also emitted from ground targets.
(1) Absorption. Absorption occurs when radiation penetrates a surface and is in-
corporated into the molecular structure of the object. All objects absorb incoming inci-
dent radiation to some degree. Absorbed radiation can later be emitted back to the atmos-
phere. Emitted radiation is useful in thermal studies, but will not be discussed in detail in
this work (see Lillisand and Keifer [1994] Remote Sensing and Image Interpretation for
information on emitted energy).
(2) Transmission. Transmission occurs when radiation passes through material and
exits the other side of the object. Transmission plays a minor role in the energy's interac-
tion with the target. This is attributable to the tendency for radiation to be absorbed be-
fore it is entirely transmitted. Transmission is a function of the properties of the object.
(3) Reflection. Reflection occurs when radiation is neither absorbed nor transmit-
ted. The reflection of the energy depends on the properties of the object and surface
roughness relative to the wavelength of the incident radiation. Differences in surface
properties allow the distinction of one object from another.
(a) Absorption, transmission, and reflection are related to one another by
EI = EA + ET +ER
(2-6)
where
EI
=
incident energy striking an object
EA
=
absorbed radiation
ET
=
transmitted energy
ER
=
reflected energy.
2-21
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