2. TODAY’ S TOPIC
DEFINITION OF ELECTROMAGNETIC ENERGY
CLASSIFICATION OF ENERGY INTERACTION
ENERGY BALANCE RELATIONSHIP
FACTORS CONTROLLING ENERGY INTERACTION WITH
EARTH SURFACE FEATURES
MATERIALS CONSTITUTING EARTH SURFACE
WAVELENGTH OF ENERGY
CONDITION OF FEATURES
3. DEFINITION OF ELECTROMAGNETIC ENERGY
a form of energy that is reflected or emitted from objects in the
form of electrical and magnetic waves that can travel through space.
can be detected only when it interacts with matters
There are many forms of electromagnetic energy including gamma
rays, x rays, ultraviolet radiation, visible light, infrared radiation,
microwaves and radio waves.
4. Electromagnetic energy is incident on any earth
Surface feature
Three fundamental energy interactions with
the feature are possible
5. transmission (T) occurs
when radiation passes
through a target
Reflection (R) occurs when Absorption (A) occurs when
radiation "bounces" off the radiation (energy) is
target and is redirected. absorbed into the target
6. INCIDENT ENERGY (EI)
REFLECTED ENERGY (ER)
WATER SURFACE
ABSORBED
ENERGY
(EA)
TRANSMITTED ENERGY (ET)
BASIC INTERACTIONS BETWEEN ELECTROMAGNETIC ENERGY
AND AN EARTH SURFACE FEATURE ( WATER BODY )
7. Proportion of the
energy is
absorbed,
transmitted or
reflected by a
material will
depend upon
8. IN REMOTE SENSING, WE ARE MOST
INTERESTED IN MEASURING THE
RADIATION REFLECTED FROM
TARGETS.
Reflection from surfaces
occurs in two ways:
9. SPECULAR REFLECTORS
gives the mirror-like reflection of light (or of
other kinds of wave) from a surface.
in which light from a single incoming
direction (a ray) is reflected into a single
outgoing direction.
the angle of incidence equals the angle of
reflection (θi = θr in the figure),
SPECULAR REFLECTORS
Reflections on still water are an example
of specular reflection
10. DIFFUSE REFLECTORS
gives the reflection of light
from a surface such that an
incident ray is reflected at
many angles
rough surface
DIFFUSE REFLECTORS does not give rise to images.
11. ELECTROMAGNETIC SPECTRUM
The "electromagnetic spectrum" of an object is
the characteristic distribution of electromagnetic
radiation emitted or absorbed by that particular
object.
provides an illustrated method to show the
types of electromagnetic radiation in terms of
wavelength and frequency.
12. Here are the different types of radiation in the EM spectrum,
in order from lowest energy to highest:
RADIO WAVE :
kind of energy that radio stations emit into the air.
emitted by other things,such as stars and gases in space.
MICRO WAVE :
in space are used by astronomers to learn about the structure of
nearby galaxies, and our own Milky Way
cook your popcorn in just a few minutes!
INFRARED :
Our skin emits infrared light, which is why we can be seen in
the dark by someone using night vision goggles
IR light maps the dust between stars.
VESIBLE :
this is the part that our eyes see
emitted by everything from fireflies to light bulbs to stars also by
fast-moving particles hitting other particles.
ULTRA-VIOLET :
Stars and other "hot" objects in space emit UV radiation.
cause our skin to burn
X-RAY:
Your doctor uses them to look at your bones and your
dentist to look at your teeth
GAMMA-RAY :
Radioactive materials (some natural and others made by man in
things like nuclear power plants) can emit gamma-rays
13.
14. Characterizes any given surface is dictated by
the surface’s roughness in comparison to the
wavelength of the energy incident upon it
Sandy
beach
15. SPECTRAL REFLECTANCE (Rλ)
reflected energy from earth surface is measured as function of
wavelength
SPECTRAL REFLECTANCE
ER(λ)
Rλ = EI(λ)
Energy of wavelength λ reflected from the object
= x 100
Energy of wavelength λ incident upon the object
16. A graph of spectral reflectance of an object as a function of wavelength
Clear water:
Clear water has a low spectral reflectance (<
10%) in the visible region
At wavelengths longer than 0.75 µm, water
absorbs almost all the incoming energy
Vegetation :
generally has three reflectance valleys.
one at the red spectral wavelength region
(0.65 µm) is caused by high absorptance of
energy by chlorophyll a and b in the leaves.
other two at 1.45-1.55 µm and 1.90-1.95 µm
are caused by high absorptance of energy by
water in the leaves
Dry soil :
has a relatively flat reflectance curve
When it is wet, its spectral reflectance drops
due to water absorption
17. Body of the feature is HOTTER than its surroundings
emits more radiation Absorbs less radiation
tends to cool
Body of the feature is COOLER than its surroundings
emits less radiation Absorbs more radiation
tends to warm
