Download Thermal Infrared Remote Sensing

Introduction of Remote Sensing
Ding Jianli
College of Resources and Environmental Science,
Postdoctoral Station of Theoretical Economics,
Xinjiang University
E-mail: [email protected]
Reference Books
1. Japan Association of Remote Sensing: Remote
Sensing Note ( 1999 )
2. John R. Jensen: Remote Sensing of the
Environment – An Earth Resource Perspective
( 2000)
3. John R. Jensen: Introductory Digital Image
Processing – A Remote Sensing Perspective
( 1996 )
4. W.G. Rees: Physical Principles of Remote
Sensing ( 2001 )
Chapter 1
Fundamentals of Remote
Sensing
1.1 Concept of Remote
Sensing
Data Collection
There are two way for Data Collection
normally:
 take place directly in field – in situ or
in-place data collection;
 At some remote distance from the
subject matter – remote sensing data
collection
 ASPRS
(American Society for
Photogrammetry and Remote Sensing)
Definition: Remote sensing is the art,
science, and technology of obtaining
reliable information about physical
objects and the environment, through
the process of recording, measuring and
interpreting imagery and digital
representations of energy patterns
derived from noncontact sensor system
( Colwell, 1997 )
Concept of Remote Sensing
 Remote
sensing is the science and
technology by which the
characteristics of objects of interest
can be identified, measured or
analyzed the characteristics without
direct contact [Japan Association of
Remote Sensing, 1999]
Concept of Remote Sensing
Two Key Points
 “remote”: without direct contact
object;
 “sensing”: obtain object information
Remote Sensing: Maximal Definition
The acquiring of data about an object
without touching it [2]
Electro-magnetic radiation which is
reflected or emitted from an object is the
usual source of remote sensing data.
However any media such as gravity or
magnetic fields can be utilized in remote
sensing [1]
Minimal Definition
The noncontact recording of information from
the ultraviolet, visible, infrared, and
microwave regions of the electromagnetic
spectrum by means of instruments such as
cameras, scanners, lasers, linear arrays,
and/or area arrays located on platforms such
as aircraft or spacecraft, and the analysis of
acquired information by means of visual and
digital image processing [2]
Max – Min = ?
 Other
electromagnetic wave
remote sensing: X-ray remote
sensing, Geophysics invitation, ..
 Mechanical wave remote sensing:
sound wave, earthquake wave, …
 Gravity wave remote sensing
…
Sensor
 A device
to detect the electro-magnetic
radiation reflected or emitted from an
object is called a "remote sensor" or
"sensor“[1].
 cameras, scanners, lasers, linear
arrays, and/or area arrays, radar are
sensor which are often used in remote
sensing
Platform
 A vehicle
to carry the sensor is
called a "platform".
 Aircraft or satellites are platforms
which are often used in remote
sensing .
Most simple remote sensing
遥感的基本原理示意图
遥感的基本原理示意图
遥感基本原理示意图
Why can be remote sensing

each object has a unique and different
characteristics of reflection or emission if
the type of object or the environmental
condition is different. Remote sensing is a
technology to identify and understand the
object or the environmental condition
through the uniqueness of the reflection or
emission.
A. Electro-magnetic radiation source;
B. Interaction of Electro-magnetic radiation
with atmosphere;
C. Interaction of Electro-magnetic radiation
with object;
D. Sensor record electro-magnetic radiation
from object;
E. Data transmission, receiving, and
processing;
F. Data interpretation and analysis;
G. Remote sensing application
1.2 Characteristics of ElectroMagnetic Radiation
Electro-magnetic radiation
 A carrier
of electro-magnetic
energy by transmitting the
oscillation of the electro-magnetic
field through space or matter. It has
the characteristics of both wave
motion and particle motion.
电磁波
电磁波的波长
电磁波波长、频率
The four elements of electromagnetic radiation
 Frequency
(or wavelength);
 Transmission direction;
 Amplitude;
 Plane of polarization.
1.3 Electro-magnetic Radiation
Spectrum
Visible light
spectrum
Visible light
根据辐射特性，将红外波段
分为反射红外和辐射红外
（热红外）两部分。
Microwave
1.4 Types of Remote Sensing
with Respect to Wavelength
Regions
 Visible
and Reflective Infrared
Remote Sensing,
 Thermal Infrared Remote Sensing
 Microwave Remote Sensing
Visible and Reflective
Infrared Remote Sensing
 The
energy source is the sun.
 Remote sensing data obtained
mainly depends on the reflectance
of objects
Thermal Infrared Remote
Sensing
 The
source of radiant energy is the
object itself
 Remote sensing data obtained
mainly depends on the thermal
radiation of objects
Two Type of Microwave
Remote Sensing
1.
2.
Passive microwave remote sensing:
the microwave radiation emitted
from an object is detected;
Active micro wave remote sensing:
detects the back scattering of the
radiation and can measure back
scattering coefficient of object
Passive
remote
sensing
Active
remote
sensing
1.5 Black Body Radiation
Thermal radiation depending on the
temperature and emissivity of the object.
Thermal radiation can be expressed in terms
of black body theory;
 Black body radiation is defined as thermal
radiation of a black body, and can be given
by Plank's law as a function of temperature
T and wavelength

 A correction
for emissivity should be
made because normal observed objects
are not black bodies;
 The temperature of the black body
which radiates the same radiant energy
as an observed object is called the
brightness temperature of the object.
1. 6 Reflectance
 Reflectance
is defined as the ratio of
incident flux on a sample surface to
reflected flux from the surface
 A basic assumption in remote sensing
is that spectral reflectance is unique
and different from one object to an
unlike object
Reflectance Factor and
Spectral Reflectance
 Reflectance
factor is sometime used
as the ratio of reflected flux from a
sample surface to reflected flux from a
perfectly diffuse surface.
 Spectral Reflectance is reflectance
with respect to wavelength is called
Perfectly Diffuse Surface
 A Perfectly
Diffuse Surface is defined
as a uniformly diffuse surface with a
reflectance of 1, while the uniformly
diffused surface, called a Lambertian
Surface, reflects a constant radiance
regardless of look angle.
Bidirectional Reflectance
 Reflectance
with a specified incident
and reflected direction of electromagnetic radiation or light is called
directional reflectance
 if incident and reflection are both
directional, such reflectance is called
bidirectional reflectance
吸收、透射、反射
Diffuse Reflection
1.7 Spectral Characteristics of
Solar Radiation
 The
sun is the energy source used
to detect reflective energy of
ground surfaces in the visible and
near infrared regions.
 The sun is considered as a black
body with a temperature of 5,900
K.
 The
incident solar radiation at the
earth's surface is very different to that
at the top of the atmosphere due to
atmospheric effects
 The solar spectral irradiance at the
earth's surface is influenced by the
atmospheric conditions and the zenith
angle of the sun.
Sky Radiation

Beside the direct sunlight falling on a
surface, there is another light source called
sky radiation, diffuse radiation or
skylight, which is produced by the
scattering of the sunlight by atmospheric
molecules and aerosols.
 The
skylight is about 10 percent
of the direct sunlight when the sky
is clear and the sun's elevation
angle is about 50 degree. The
skylight has a peak in its spectral
characteristic curve at a
wavelength of 0.45 m.
1.8 Transmittance of the
Atmosphere
Absorption and Scattering
The sunlight's transmission through the
atmosphere is affected by Absorption and
Scattering of atmospheric molecules and
aerosols.
 The reduction of sunlight intensity is called
Extinction. The rate of absorption
scattering, and extinction are expressed as
Absorption, Scattering, and Extinction
coefficient respectively.

Optical Thickness
The optical thickness of the atmosphere
corresponds to the integrated value of the
extinction coefficient at each altitude by
the atmospheric thickness.
 The optical thickness indicates the
magnitude of absorption and scattering of
the sunlight.

The following two type elements will
influence the transmittance of the
atmosphere.
 Atmospheric molecules (smaller size than
wavelength):
CO2 (carbon dioxygen), O3 (ozone ), N
(nitrogen ), and other molecules
 Aerosols (larger size than wavelength):
water drops such as fog and haze, smog,
dust and other particles with a bigger size
Scattering by atmospheric molecules
Scattering by atmospheric molecules with a
smaller size than the wavelength of the
sunlight is called Rayleigh scattering.
 Raleigh scattering is inversely proportional
to the fourth power of the wavelength.
 The contribution of atmospheric molecules
to the optical thickness is almost constant
spatially and with time, although it varies
somewhat depending on the season and the
latitude.

Scattering by aerosols
 Scattering
by aerosols is called Mie
scattering.
 The source of aerosols will be suspended
particles such as sea water or dust in the
atmosphere blown from the sea or the
ground, urban garbage, industrial smoke,
volcanic ashes etc., which varies to a
great extent depending upon the location
and the time.
 In
addition, the optical characteristics
and the size distribution also changes
with respect to humidity, temperature
and other environmental conditions.
This makes it difficult to measure the
effect of aerosol scattering.
1.8 Radiative Transfer Equation
 Radiative
Transfer is defined as the
process of transmission of the electromagnetic radiation through the
atmosphere, and the influence of the
atmosphere.
 The atmospheric effect is classified
into multiplicative effects and additive
effects
The multiplicative effect comes from the
extinction by which incident energy from
the earth to a sensor will reduce due to the
influence of absorption and scattering.
 The additive effect comes from the
emission produced by thermal radiation
from the atmosphere and atmospheric
scattering, which is incident energy on a
sensor from sources other than the object
being measured.

 Absorption
will occur at specific
wavelengths when the electromagnetic energy converts to thermal
energy.
 Scattering is remarkable in the shorter
wavelength region when energy
conversion does not occur but only the
direction of the path changes.
 Thermal
radiation is dominant in the
thermal infrared region, while
scattering is dominant in the shorter
wavelength region.
 Generally, as extinction and emission
occur at the same time, both effects
should be considered together in the
radiative transfer equation.
Homework 1
Give some examples of max. remote
sensing
 Why leaf is green color, and it is red color
in pseudo-color image ?
 Clear air and sea water are blue color,
sometimes water is yellow or green color,
why?
