Introduction to Remote Sensing
History
EMR
EMS
Radiation Characteristics
Spectral Signatures
Introduction to GIS: Lecture #9 (Remote Sensing)
LANDSAT Imagery
Introduction to GIS: Lecture #9 (Remote Sensing)
Remote Sensing
A technique of obtaining information about
objects through the analysis of data
collected by special instruments that are not
in physical contact with the objects of
investigation.
Reconnaissance from a distance.
Introduction to GIS: Lecture #9 (Remote Sensing)
History
1839 - first photograph
1858 - first photo from a balloon
1903 - first plane
1909 first photo from a plane
1903-4 -B/W infrared film
WW I and WW II
1960 - space
Introduction to GIS: Lecture #9 (Remote Sensing)
Electromagnetic Radiation (EMR)
wavelength
frequency
Introduction to GIS: Lecture #9 (Remote Sensing)
Electromagnetic Radiation
Light - can be thought of as a wave in the 'electromagnetic field' of the universe
Wavelength
Frequency
(how many times peak
passes per second)
A wave can be characterized by its wavelength or its frequency
Introduction to GIS: Lecture #9 (Remote Sensing)
EMR
Remote sensing is concerned with the
measurement of EMR returned by the
earth’s natural and cultural features that
first receive energy from the sun or an
artificial source such as a radar
transmitter.
Introduction to GIS: Lecture #9 (Remote Sensing)
EMR
Because different objects return different
types and amounts of EMR, the objective in
remote sensing is to detect these differences
with the appropriate instruments.
This, in turn, makes it possible for us to
identify and assess a broad range of
surficial features and their conditions.
Introduction to GIS: Lecture #9 (Remote Sensing)
Electromagnetic Spectrum
Ranges From:
Gamma rays (short wavelength, high
frequency and high energy content)
To:
Passive radio waves (long wavelength, low
frequencies, and low energy content).
Introduction to GIS: Lecture #9 (Remote Sensing)
EMS
A spectral band is composed of some
defined group of continuous spectral lines,
where a line represents a single wavelength
or frequency. The boundaries between most
of the bands are arbitrarily defined because
each portion overlaps adjacent portions.
Introduction to GIS: Lecture #9 (Remote Sensing)
EMS
centimeter
millimeter
micrometer
nanometer
angstrom
=
=
=
=
=
.01 meters
.001 meters
.000,000,1 meters
.000,000,000,1 meters
.000,000,000,01 meters
Introduction to GIS: Lecture #9 (Remote Sensing)
The EM Spectrum
1020 Hz
Gamma
Rays
1 pm
1018 Hz
X-Rays
10pm
1016 Hz
UV
1014 Hz
visi- N. Mid Th.
ble IR IR IR
10 nm
Blue
0.4 m
1 micron
green
0.5 m
yellow
0.6 m
1012 Hz
1010 Hz
Microwaves
Far IR
Radar
100 microns
1 mm
TV FM
Radiowaves
100 mm
red
0.7 m
Different wavelengths of light can be grouped together
into different types
Visible light contains light from 0.4 to 0.7 micrometers
Infrared light from 0.1 micrometers to 1 millimeter
Introduction to GIS: Lecture #9 (Remote Sensing)
Radiation
Introduction to GIS: Lecture #9 (Remote Sensing)
R/S Spectral Regions
Ultraviolet (UV)
Visible
Infrared (IR)
Microwave
Introduction to GIS: Lecture #9 (Remote Sensing)
R/S Spectral Regions
Introduction to GIS: Lecture #9 (Remote Sensing)
R/S Spectral Regions
Traditionally, the most common used
region of the EMS in remote sensing has
been the visible band. Its wavelength span
is from 0.4 to 0.7 micrometers, limits
established by the sensitivity of the human
eye.
Introduction to GIS: Lecture #9 (Remote Sensing)
R/S Spectral Regions
Introduction to GIS: Lecture #9 (Remote Sensing)
Visible Light
Composed of colors (different
wavelengths)
These familiar colors range from violet
(shortest wavelength) through indigo,
blue, green, yellow, orange and red
(ROYGBIV).
Introduction to GIS: Lecture #9 (Remote Sensing)
Color
The visible spectrum is also viewed as being
composed of three equal-wavelength segments
that represent the additive primary colors;
Blue (0.4 to 0.5 micrometers)
Green (0.5 to 0.6 micrometers)
Red ( 0.6 to 0.7 micrometers)
Introduction to GIS: Lecture #9 (Remote Sensing)
Primary Colors
A primary color is one that cannot be made
from any other color. All colors perceived
by the human optical system can be
produced by combining the proper
proportions of light representing the three
primaries. This principle forms the basis for
the operation of the color TV.
Introduction to GIS: Lecture #9 (Remote Sensing)
Color
The chlorophyll of healthy grass
selectively absorbs more of the blue and
red wavelengths of white light and
reflects relatively more of the green
wavelengths to our eyes.
Introduction to GIS: Lecture #9 (Remote Sensing)
Infrared (IR) Band
The infrared (IR) band has wavelengths
between red visible light (0.7 micrometers)
and microwaves at 1,000 micrometers.
Infrared means “below the red.”
In remote sensing the IR band is usually
divided into two components that are based
on basic property differences;
Reflected IR band
Emitted/Thermal IR band
Introduction to GIS: Lecture #9 (Remote Sensing)
Reflected IR
The reflected IR band represents reflected
solar radiation which behaves like visible
light. Its wavelength span is from 0.7 to
about 3 micrometers.
Introduction to GIS: Lecture #9 (Remote Sensing)
Thermal IR (Heat)
The dominant type of energy in the thermal
IR band is heat energy, which is
continuously emitted by the atmosphere
and all objects on the earth’s surface. Its
wavelength span is from about 3
micrometers to 1,000 micrometers or 0.1
centimeters.
Introduction to GIS: Lecture #9 (Remote Sensing)
Microwave Band
The microwave band falls between the IR
and radio bands and has a wavelength
range extending from approximately 0.1
centimeters to 1 meter.
Introduction to GIS: Lecture #9 (Remote Sensing)
Microwave Band
At the proper wavelengths microwave
radiation can pass through;
- clouds
- precipitation
- tree canopies
- dry surficial deposits such as;
- sand and
- fine-grained alluvium
Introduction to GIS: Lecture #9 (Remote Sensing)
Microwave Sensors
Passive Microwave - detect natural
microwave radiation that is emitted from
the earth’s surface.
RADAR - propagates artificial
microwave radiation to the surface and
detects the reflected component.
Introduction to GIS: Lecture #9 (Remote Sensing)
Solar and Terrestrial Radiation
Most remote sensing systems are designed to
detect;
solar radiation which passes through the atmosphere
and is reflected in varying degrees by the earth’s
surface features.
terrestrial radiation which is continuously emitted by
these same features.
Introduction to GIS: Lecture #9 (Remote Sensing)
Solar and Terrestrial Radiation
Introduction to GIS: Lecture #9 (Remote Sensing)
Solar and Terrestrial Radiation
99% of the sun’s radiation falls between wavelengths of
0.2 and 5.6 micrometers.
80% is contained in wavelengths between 0.4 and 1.5
micrometers (visible and reflected IR), to which the
atmosphere is quite transparent.
Maximum radiation occurs at a wavelength of 0.48
micrometers in the visible band.
Introduction to GIS: Lecture #9 (Remote Sensing)
Solar and Terrestrial Radiation
About half the solar radiation passes through the
earth’s atmosphere and is absorbed in varying degrees
by surface features of the earth.
Most of this absorbed radiation is transformed into
low-temperature heat (warming the surface), which is
continuously emitted back into the atmosphere at
longer thermal IR wavelengths.
The earth’s land and water surface has an ambient
temperature of about 300oK
(80oF)
Introduction to GIS: Lecture #9 (Remote Sensing)
Solar and Terrestrial Radiation
Because the wavelengths covering most of the
earth’s energy output are several times longer than
those covering most of the solar output, terrestrial
radiation is frequently called longwave radiation
and solar radiation is termed shortwave radiation.
Introduction to GIS: Lecture #9 (Remote Sensing)
Solar and Terrestrial Radiation
Longwave radiation is also emitted by;
- the atmosphere’s gasses and clouds and
- from artificially heated objects on the earth’s
surface such as
- from buildings
- steam lines
- certain industrial effluents.
Introduction to GIS: Lecture #9 (Remote Sensing)
Radiation-Matter Interactions
EMR manifests itself only through its
interactions with matter which can be in the
form of;
a gas
a liquid
a solid
Introduction to GIS: Lecture #9 (Remote Sensing)
Radiation-Matter Interactions
When EMR strikes matter, EMR may be;
transmitted
reflected
scattered
absorbed
Introduction to GIS: Lecture #9 (Remote Sensing)
Radiation-Matter Interactions
Introduction to GIS: Lecture #9 (Remote Sensing)
Radiation-Matter Interactions
The amount on interaction depends upon;
the composition and physical properties of the
medium.
the wavelength or frequency of the incident
radiation.
the angle at which the incident radiation
strikes a surface.
Introduction to GIS: Lecture #9 (Remote Sensing)
Transmission
Transmission is the process by which
incident radiation passes through matter
without measurable attenuation. The
substance is thus transparent to the
radiation.
Introduction to GIS: Lecture #9 (Remote Sensing)
Transmission
Transmission through material media of
different densities (such as air to water)
causes the radiation to be refracted or
deflected from a straight-line path with an
accompanying change in its velocity and
wavelength; frequency always remains
constant.
Introduction to GIS: Lecture #9 (Remote Sensing)
Reflection
Reflection (also called specular reflection)
is the process where incident radiation
“bounces off” the surface of the substance
in a single, predictable direction.
Introduction to GIS: Lecture #9 (Remote Sensing)
Reflection
The angle of reflection is always equal and
opposite to the angle of incidence.
Reflection is caused by surfaces that are
smooth relative to the wavelength of the
incident radiation. These smooth mirrorlike surfaces are called specular reflectors.
Specular reflection causes no change to
either EMR velocity or wavelength.
Introduction to GIS: Lecture #9 (Remote Sensing)
Scattering
Scattering (also called diffuse reflection)
occurs when incident radiation is dispersed
or spread out unpredictable in many
different directions, including the direction
from which it originated.
Introduction to GIS: Lecture #9 (Remote Sensing)
Scattering
In the real world, scattering is much more
common than reflection.
The scattering process occurs with surfaces that
are rough relative to the wavelengths of incident
radiation.
Such surfaces are called diffuse reflectors. EMR
velocity and wavelength are not affected by the
scattering process.
Introduction to GIS: Lecture #9 (Remote Sensing)
Absorption
Absorption is the process by which incident
radiation is taken in by the medium. For
this to occur, the substance must be opaque
to the incident radiation.
Introduction to GIS: Lecture #9 (Remote Sensing)
EMR - Atmosphere Interactions
Areas of the spectrum where specific
wavelengths can pass relatively unimpeded
through the atmosphere are called
transmission bands or atmospheric
windows.
Introduction to GIS: Lecture #9 (Remote Sensing)
EMR - Atmosphere Interactions
Absorption bands define those areas where
specific wavelengths are totally or partially
blocked.
Introduction to GIS: Lecture #9 (Remote Sensing)
EMR - Atmosphere Interactions
To observe the earth’s surface different
remote sensing instruments have been
designed to operate within the windows
where the atmosphere will transmit
sufficient radiation for detection.
Introduction to GIS: Lecture #9 (Remote Sensing)
EMR - Atmosphere Interactions
EMR interacts with the atmosphere in the
following ways;
it may be absorbed and re-radiated at longer
wavelengths, which causes the air temperature to rise.
it may be reflected and scattered without change to
either its velocity or wavelength.
it may be transmitted in a straight-line path directly
through the atmosphere.
Introduction to GIS: Lecture #9 (Remote Sensing)
EMR - Atmosphere Interactions
Introduction to GIS: Lecture #9 (Remote Sensing)
Atmospheric Absorption and
Transmission
Significant absorbers of EMR in the
atmosphere;
oxygen
nitrogen
ozone
carbon dioxide
water vapor
Introduction to GIS: Lecture #9 (Remote Sensing)
Atmospheric Absorption and
Transmission
Introduction to GIS: Lecture #9 (Remote Sensing)
Atmospheric Scattering
EMR within certain sections of the UV,
visible and reflected IR bands is scattered
by the atmosphere.
Important scattering agents include;
gas molecules
suspended particulates
clouds
Introduction to GIS: Lecture #9 (Remote Sensing)
Atmospheric Scattering
In addition, clouds absorb most of the longwave
radiation emitted by the earth’s surface, essentially
closing the thermal IR windows.
This is why cloudy nights tend to be warmer than clear
nights. Only microwave radiation with wavelengths
longer than about 0.9 cm is capable of penetrating
clouds.
Introduction to GIS: Lecture #9 (Remote Sensing)
Atmospheric Scattering
Important scattering agents include;
gas molecules
suspended particulates
clouds
Introduction to GIS: Lecture #9 (Remote Sensing)
Atmospheric Scattering
There are three types of atmospheric
scattering important to remote sensing;
Rayleigh or molecular scattering
Mie or non-molecular scattering
Non-selective scattering
Introduction to GIS: Lecture #9 (Remote Sensing)
Rayleigh or Molecular Scattering
primarily caused by oxygen and nitrogen
molecules whose diameters are, at least, 0.1
times smaller than the affected
wavelengths.
Rayleigh scattering is highly selective
being inversely proportional to the fourth
power of the wavelength.
Introduction to GIS: Lecture #9 (Remote Sensing)
Mie or non-molecular scattering
occurs when there are sufficient particles in
the atmosphere that have diameters from
about 0.1 to about 10 times larger than the
wavelengths under consideration.
Introduction to GIS: Lecture #9 (Remote Sensing)
Mie or non-molecular scattering
Important Mie scattering agents include;
water vapor
smoke
dust
volcanic materials
salt from evaporated sea spray
Introduction to GIS: Lecture #9 (Remote Sensing)
Non-selective scattering
is found in the lower atmosphere when
there are sufficient numbers of suspended
aerosols having diameters at least 10 times
larger than the wavelengths under
consideration.
Introduction to GIS: Lecture #9 (Remote Sensing)
Non-selective scattering
Important nonscattering agents include;
larger Mie particles
water droplets
ice crystals
Introduction to GIS: Lecture #9 (Remote Sensing)
Non-selective scattering
depends upon wavelength. Within the
visible band, colorless water droplets and
ice crystals scatter all wavelengths equally
well, causing, for example, the sunlit
surfaces of clouds to appear brilliant white.
Introduction to GIS: Lecture #9 (Remote Sensing)
Skylight and Haze
The clear sky is a source of illumination
because its gasses preferentially scatter the
shorter wavelengths of sunlight.
This diffuse radiation is called sunlight or
sky radiation.
Introduction to GIS: Lecture #9 (Remote Sensing)
Skylight and Haze
To our eyes sky radiation is manifested as
haze which causes a reduction in visibility
and also causes distant landscapes to take
on a soft, blue-gray appearance.
Atmospheric haze has important
ramifications in remote sensing.
Introduction to GIS: Lecture #9 (Remote Sensing)
Skylight and Haze
In the short wavelength region, radiation
reaching an airborne or spaceborne sensor
consists of two components;
radiation that is scattered by the earth’s
surface and then reaches the sensor
without being affected by the intervening
atmosphere.
radiation that is scattered by the
atmosphere, either before or after it
reaches the earth’s surface.
Introduction to GIS: Lecture #9 (Remote Sensing)
Skylight and Haze
The radiation scattered by the atmosphere
contains no information about the earth’s
surface, and it acts as a masking agent
when a remote sensing system records
these wavelengths.
Introduction to GIS: Lecture #9 (Remote Sensing)
Skylight and Haze
The net effect of this extra illumination, or
non-image forming “haze light”, is a loss of
detail and a reduction in scene contrast.
Haze is visualized as a fog-like veil in
black and white photos and as an overall
blueish tint in a color photo.
Introduction to GIS: Lecture #9 (Remote Sensing)
EMR - Surface Interactions
The natural and cultural features of the
earth’s surface interact differently with
solar radiation.
Albedo or Spectral Reflectance is the
percentage radiation reflected by an object.
Introduction to GIS: Lecture #9 (Remote Sensing)
EMR - Surface Interactions
Introduction to GIS: Lecture #9 (Remote Sensing)
Spectral Signatures
Every natural and synthetic object reflects
and emits EMR over a range of
wavelengths in its own characteristic
manner according , in large measure, to its
chemical composition and physical state.
Introduction to GIS: Lecture #9 (Remote Sensing)
Spectral Signatures
Spectral signatures are the distinctive
reflectance and emittance properties of
objects.
Within some limited spectral region, a
particular object will usually exhibit a
unique spectral response pattern that differs
from that of other objects.
Introduction to GIS: Lecture #9 (Remote Sensing)
Spectral Signatures
Remote sensing depends upon operation in
wavelength regions of the spectrum where
these detectable differences in reflected and
emitted radiation occur.
Introduction to GIS: Lecture #9 (Remote Sensing)
Spectral Signatures
The diagnostic response patterns of that
make it possible to discriminate objects
(spectral signatures) often lie beyond the
narrow confines of the visible spectrum
where no detectable differences occur.
Introduction to GIS: Lecture #9 (Remote Sensing)
Spectral Signatures
Detectors translate the sensed radiation into
electrical energy which is used to drive
invisible-to-visible translation devices.
Introduction to GIS: Lecture #9 (Remote Sensing)
Spectral Signatures
Radiometer measurements are used to
prepare spectral signature curves which are
line plots showing the radiation intensity
for various features as a function of
wavelength.
Here are typical spectral signature curves
for three common materials; vegetation,
soil and water.
Introduction to GIS: Lecture #9 (Remote Sensing)
Spectral Signatures
Introduction to GIS: Lecture #9 (Remote Sensing)
LANDSAT Imagery
Introduction to GIS: Lecture #9 (Remote Sensing)