Remote Sensing

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Remote Sensing

• Topic 1 Fundamentals of
• Remote Sensing
• Chapter 1 Lillesand and Keifer

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• Remote Sensing
• Defn.
• The science, art and technology associated with
  the acquisition and analysis of data about an
  object, area, or phenomenon without direct
  contact

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A Simple RS System
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Elements of a CompleteRemote Sensing System
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Data Acquisition
a) Energy Source EMR from Sun, flashbulb, or
transmitted from antenna
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Data Acquisition
b) Propagation reflection, refraction and
absorption of energy as it moves toward object of
interest
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Data Acquisition
c) Incident Energy reflection, refraction and
absorption of energy as it strikes object of
interest
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Data Acquisition
b) Propagation reflection, refraction and
absorption of energy as it moves away from object
of interest
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Data Acquisition
d) Sensor and Platform detection, quantification
and recording energy in various wavelengths
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Data Acquisition
f) Data Products - distribution of data in hard
copy or digital format
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Data Analysis
g) Interpretation and Analysis - extraction of
information through visual interpretation,
photogrammetric techniques and digital image
analysis
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Data Analysis
Reference Data maps, photographs, reports, and
other ancillary data used to facilitate analysis
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Data Analysis
h) Information Products computer display, maps,
reports, geospatial databases, etc.
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Data Analysis
i) Users managers, politicians, policy makers
that use information to make decisions
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Airphoto Interpretation

• Defn
• The analysis of all types of aerial photography
  to extract quantitative and qualitative
  information
• Uses a variety of cameras, films and filters
• Includes photogrammetry

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Photogrammetry

• Defn
• Extraction of quantitative information
• Typically uses vertical photos
• Includes measures of
• Distance
• Area
• Direction
• and Height

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EMR

• EMR is energy
• Sun is most common source
• Detected by passive RS systems

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EMR

• Modern physics acknowledges dual nature of EMR
• The wave-particle duality refers to how EMR of
  differing wavelengths behaves, not what it is
• Low frequency EMR tends to act more like a wave
  higher frequency EMR tends to act more like a
  particle

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Wave Model

• EMR travels as a set of sinusoidal orthogonal
  harmonic waves travelling at the speed of light,
  (c 3.0x108ms-1)

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Wave Model

• Wavelength (?) is the distance between successive
  waves measured in micrometers (1 ?m 1x10-6m).

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Wave Model

• Frequency (v) is the number of waves (cycles)
  passing a fixed point in a given period of time
  measured in cycles per second or hertz.

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Wave Model

• Wavelength and frequency are related to the speed
  of light as follows c ?v
• ? c/v
• v c/?

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Particle Model

• EMR is comprised of tiny particles (quanta)
  called photons travelling in a wave-like pattern
  at the speed of light
• Intensity is proportional to number of photons
• Total amount of energy is related to wavelength
  and frequency by Plancks constant (h)
• Q hv
• Q hc/?
• where Q energy of a quantum

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EMR
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EMR and Remote Sensing

• All RS systems obtain information by measuring
  and recording EMR received at the sensor
• All objects interact (reflect, refract, absorb)
  with incident EMR differently
• In addition, all objects above absolute zero (0º
  K) emit EMR directly proportional to their
  temperature

All RS systems discussed in this course deal
with the detection of EMR, however, there are RS
systems that are based on the detection of sound
waves, gravity, and electrical resistivity.
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The Foundation of RS

• Differences in how features interact with and
  emit EMR allow us to distinguish between objects
  based on their unique spectral characteristics or
  signatures
• Variations are wavelength dependant some things
  may look the same at certain wavelengths but
  different in others

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Radiance of EMR

• A black body is hypothetical material that
  absorbs and re-radiates ALL incident EMR.
• The Stephan-Boltzman equation describes the total
  amount of radiation emitted by a black body as a
  function of its surface temperature
• M sT4
• where M energy (Wm-2)
• s Stephan-Boltzman constant
• T temperature (K)

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Total EMR Emitted

• The higher the temperature the more total energy

Total Energy Area Under Curve
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Wavelength of EMR Emitted

• The higher the temperature the lower/shorter the
  wavelength of maximum radiance
• Wein Law states that ?m A/T 
• where A is a constant

Shortwave EMR
Longwave EMR
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Atmospheric EMR Interactions

• Atmospheric interactions include reflection,
  scattering and absorption of EMR
• EMR that is not scattered or absorbed is simply
  transmitted through the atmosphere unaltered
  this is good
• Some wavelengths of the EMS are so effectively
  scattered or absorbed that very little EMR
  reaches Earths surface this is bad

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Transmission of EMR

• Propagation of EMR through the material/object
  with no interaction
• Path of EMR can be deflected or refracted as it
  passes through materials of differing density
• Results in a change in velocity and wavelength
  but not frequency

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Scattering EMR Interactions

• Occurs when EMR bounces in all directions off
  gas molecules and particles in the atmosphere
• Doesnt alter the incident EMR but may filter out
  a large proportion of it

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Ralyleigh Scatter

• Occurs when EMR is scattered by gas molecules and
  particles smaller than ?
• Scattering is diffuse (in all directions) and ?
  dependent or selective
• Scattering 1/ ?4

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Mie Scatter

• Occurs when EMR is scattered by particles larger
  than ?
• Scattering is predominantly forward and is not ?
  dependent

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Absorption of EMR

• Occurs in atmosphere and at Earths surface
• Incident EMR is typically converted to sensible
  heat energy and used to raise temperature of
  surface or object
• Essentially, incident SW EMR is absorbed and
  reradiated as outgoing LW EMR
• Absorption is wavelength dependent

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Reflected EMR

• Also occurs in atmosphere and at Earths surface
• Two types of reflection dependent on roughness of
  surface or object

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Specular Reflection

• Incident EMR is reflected away from the surface
  like a mirror
• angle of incidence equals angle of reflection.
• Most common with smooth surfaces

• Non-selective, all wavelengths are reflected
  equally
• So no information about the object

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Diffuse (Lambertian) Reflection

• Occurs when incident EMR bounces off a material
  and scatters in all directions
• Wavelength selective so diffusely reflected EMR
  does contain information about the character of
  an object
• Most common when surface is rough compared to the
  ? of incident EMR

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Surface Energy Balance
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Overall Energy Balance
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Where Do We Look ?
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Spectral Signatures

• Reflectance is wavelength dependent
• Signatures represent average reflectance values
• Signatures are spatially and temporally variable

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Typical Spectral Signatures
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Next TopicPhotographic PrinciplesChapter 2
Lillesand and Kiefer