chapter 1: introduction - purdue university
TRANSCRIPT
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib1
Chapter 1: Introduction• Photogrammetry:
– Definition & applications– What are we trying to do?– Data acquisition systems– 3-D viewing of 2-D imagery– Automation (matching problem)
• Necessary tools:– Image formation (Chapters 2 – 4)– Mathematical image manipulation (Chapters 5 – 9)– Direct geo-referencing (Chapter 10)– Photogrammetric products – DEM and Orthophotos (Chapters
11 & 12)
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib2
CE59700: Chapter 2
Electro-Magnetic (EM) Radiation
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib3
EM Radiation: Overview• Terminology• EM radiation principles• Active versus passive remote sensing systems• Bands of the electro-magnetic radiation:
– Radio waves– Microwaves– Infrared radiation– Visible light– Ultraviolet rays– X-rays– Gamma rays
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib4
Terminology and EM Radiation Principles
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib5
Terminology• Energy (I) is the capacity to do work.
– It is expressed in joules (J).• Radiant energy is the energy associated with
electromagnetic radiation.• Radiant flux (Φ) is the rate of transfer of energy from
one place to another (e.g., from the Sun to the Earth).– Radiant flux is measured in watts (J/sec).– Φ = ∂ Ι / ∂ t
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib6
Terminology• To understand the interaction between the EM radiation
and the surface of the Earth, we need to introduce the term radiant flux density.– The radiant flux that is incident upon or is emitted by a surface
per unit area.– For incident radiation, we use the term irradiance (E) to
denote the radiant flux density.– For emitted radiation, we use the term radiant exitance (M) to
denote the radiant flux density.– Radiant flux density is measured in watts per square meter
(wm-2).– E/Μ= ∂ Φ / ∂ A
• (A) refers to the area along the normal to the radiation direction.
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib7
EM Radiation• Visible light is only one of the many forms of
electromagnetic energy.• Radio waves, heat, ultraviolet rays, and x-rays are other
familiar forms.• EM-radiation can be either considered as:
– Stream of particles (photons)• Allows for a better understanding of the radiation interaction with the
surface of the Earth and its atmosphere– Waveform
• Allows for the distinction between different manifestations of radiation (e.g., microwave and infrared radiation)
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib8
λ amplitude
EM Radiation• The EM radiation travels in vacuum with the speed of
light.• The relationship between the speed, frequency, and the
wavelength of the radiation is defined by:– c (m/sec) = 𝜆 (m) * f (sec-1) (c) speed of light = 3x108 m/sec (f) frequency of the radiation (cycles/sec)
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib9
Radiation Energy• The shorter the wavelength, the higher the energy that is
carried by the radiation.• The amount of energy of a single photon is defined as:
– I (joule) = h (joule sec) f (sec-1)• h is Planck’s constant (6.3 x 10-34 joule sec)
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib10
Sources of EM radiation• Any object whose temperature is greater than 0° Kelvin
(-273° C) emits radiation.• Black material absorbs all radiation that reaches it (a
perfect absorber is referred to as a 'blackbody').• The distribution of the emitted energy at each
wavelength is not uniform.• The distribution of the emitted energy in different
regions of the spectrum depends upon the temperature of the source.
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib11
EM Radiation Source• A blackbody transforms absorbed heat into radiant
energy according to Planck’s law of spectral exitance:
]1[ /
511
2 −=
−−
TcecM λλ
λπ
• c1 = 3.742 x 10-16 (W m2)• c2 = 1.4388 x 10-2 (m K)• λ = wavelength (m)• T = Temperature (K)• Mλ = Spectral exitance per wavelength (Wm-2m-1)
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib12
Black Body Radiation
http://en.wikipedia.org/wiki/Black-body_radiation
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib13
EM Radiation Source• The integrated radiance (area under the curve) increases
as T increases.• The peak radiance shifts towards shorter wavelengths as
T increases.• The peak of the spectral exitance curve is governed by
Wein’s Displacement Law:
13max
−= Tcλ
• c3 = 2.898 x 10-3 (m K)
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib14
EM Radiation Source• The total exitance of a blackbody at temperature T is
given by the Stefan-Boltzmann Law as:
)( 24 −= mWTM σ
• σ = 5.6697 x 10-8 (W m-2 K-4)
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• The Sun is the most common source of radiation.
EM Radiation Source
http://www.nasa.gov/images/
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib16
EM Radiation Source• The distribution of the spectral exitance from a black
body at 5900°K closely approximates the Sun’s spectral exitance.
• The Earth approximately acts as a blackbody with a temperature of 290°K.
• The maximum solar radiation takes place in the visible spectrum (λmax = 0.47μm).– 46% of the Sun’s total energy falls into the visible waveband
(0.4 - 0.76 μm).
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib17
Sun/Earth Radiation
http://chartsgraphs.files.wordpress.com/2009/11/sun_earth_spec_rad1.png
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EM Radiation: Interaction with the Atmosphere
https://www.fas.org/irp/imint/docs/rst/Sect9/originals/Fig9_13.gif
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib19
Passive Versus Active Remote Sensing Systems
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib20
Active Versus Passive Sensors• Remote sensing systems can be divided into two
categories: active and passive sensors.• Active sensors send out a signal and react to the
response.– Active sensors need their own power to operate.
• Passive sensors simply process received signal from the surrounding environment (like thermometers).– Passive sensors do not need separate power to operate.
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib21
Passive Sensors (e.g., Passive Cameras)
A
a
Sensor
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Active Sensors (e.g., LiDAR & RADAR)
Sensor
A
Emitted Wave
a
Reflected Wave
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http://www.neis.gov.cn/kjddYG/index.jhtml
Active Versus Passive Sensors
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EM Radiation Wavebands
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EM Radiation Wavebands
http://foto.hut.fi/opetus/350/k04/luento6/luento6.html
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib26
Radio Waves• They are used to transmit radio and TV signals.• Wavelength ranges from less than centimeter to
hundreds of meters.• FM radio waves are shorter than AM radio waves.• Natural objects do not emit radio waves.• Radio waves are used in remote sensing to exchange
information between the satellites and the ground stations.
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib27
Microwave• It has a wavelength that extends from 1mm – 300 cm.
– This radiation can penetrate clouds (valuable region for remote sensing).
• Microwave are emitted from:– Earth surface,– Cars,– Planes, and– Atmosphere.
• Q: Should active or passive sensors be used?• The emitted microwave is function of the object’s
temperature.– The emitted energy is too small for high resolution remote
sensing.
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Microwave
Microwave Sensors
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Active Microwave• For applications with high resolution requirements, we
use active microwave remote sensing systems (RADAR):– RAdio Detection And Ranging
• Advantages of RADAR include:– All weather, day-night systems– Radiation is not scattered or absorbed by clouds– Detect roughness, slope, and electrical conductivity
information• They do not detect color and temperature information.
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RADAR
Black bulge under fuselage covers the radar antennahttp://www.tungsten-alloy.com/airborne-antenna-bases.htm
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RADAR & Visible Imagery
http://www.sandia.gov/radar/imageryku.html
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib32
Infrared (IR)• It has a wavelength that extends from 0.7μm → 1 mm.
– Near IR (0.7μm – 1.5μm) behaves like visible light and can be detected by special photographic films.
– Mid IR (1.5μm – 3.0μm) is of solar origin and is reflected by the surface of the earth.
– Thermal/Far IR (3.0μm – 15μm) is emitted by the Earth surface and can be sensed as a heat.
• The amount of emitted energy depends on the temperature of the target.• Much of the emitted energy is absorbed by the atmosphere (it heats the
atmosphere).– Sub-millimeter IR (15μm – 1mm)
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Infrared (IR)
Infrared Band
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CE 59700: Digital Photogrammetric Systems Ayman F. Habib34
Infrared (IR)• Q: Active or passive sensor?• Infrared images can give us information about:
– Health of crops– Forest fires (even under cloud coverage)– Heat leakage from houses
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Thermal Imaging
EZ THERM
Loose Connection in Breaker Boxhttp://www.electrophysics.com/
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Visible & Thermal (Far-Infrared) Imagery
https://www.fas.org/irp/imint/docs/rst/Sect13/originals/Fig13_50.jpg
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Visible & Thermal Imagery
Visible Thermal
http://www.atmarine.fi/?id=103
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Visible & Thermal Imagery
Visible Thermal
http://www.imaging1.com/thermal/thermoscope-FLIR.html
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Visible Light• It has a wavelength ranging from:
– 0.4 μm to 0.7 μm.• It contains the Blue, Green, and Red portions of the
electromagnetic spectrum.• This portion of the spectrum is sensed by the human eye
and most photographic films.• Q: Active or passive sensor
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Visible Light
Visible Sensors
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Sensors Operating in the Visible Band
RC 30http://www.leica-geosystems.com
ADS 100http://ptd.leica-geosystems.com
http://www.ziimaging.com
Z/I DMC IIe 250
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Black and White Image
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Color Image
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• Laser wavelength 500-1500 nm• Typical values 1040 – 1060 nm
LiDAR Systems
http://1.bp.blogspot.com/_nD_R3gXtq2Y/TENeUoq1T7I/AAAAAAAAAfs/8bgoq4l8D5c/s1600/Electromagnetic-Spectrum-3.png
LiDAR
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LiDAR
OPTECH ALTM 3100http://www.optech.ca/prodaltm.htm
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LiDAR
Teledyne Optech ALTM Galaxy T1000http://www.optech.ca/prodaltm.htm
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LiDAR
Leica-Geosystems: ALS 40http://www.albireo.in/data_acquisition/assets/lidar_cameras.html
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LiDAR
Leica-Geosystems: ALS 80http://www.albireo.in/data_acquisition/assets/lidar_cameras.html
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LiDAR
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LiDAR: Range/Intensity Data
Range Image Intensity Image
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Visible & LiDAR Range Imagery
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Visible & LiDAR Intensity Imagery
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Ultraviolet• It has a wavelength ranging from:
– 0.01 μm to 0.4 μm.• It is a portion of the sunlight that can burn the skin and
cause skin cancer.• This portion of the spectrum should be blocked by the
ozone in the earth’s upper atmosphere.– It is not used in satellite remote sensing.
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X-Rays• Wavelength ranging from:
– 0.01 μm to 10-5 μm.• Short wavelength → High energy content → high
penetration power• Extensively used in medical applications
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X-Rays
http://www.ieee-uffc.org/ultrasonics/software/MATLAB/Lecture6/Lecture6_4.htm
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X-Rays: Stereo-Photogrammetric Analysis
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Gamma Rays• Wavelength of approximately 3* 10-6 μm• More penetrating power than X-Rays• They are generated by radioactive atoms and nuclear
explosions.• Gamma rays from radio active material can be recorded
by low-flying aircrafts.• Due to atmospheric scattering and absorption, gamma
rays cannot be detected by satellite sensors.• They are in use in some medical applications.
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EM Radiation Wavebands: Final Remarks
Radio
Microw
ave
VHF
HFInfrared
Far
Thermal
NearVisible
Ultraviolet
0.3 μm
0.4 μm
0.5 μm
0.6 μm
0.7 μm
0.8 μm
0.1 μm
1 μm
10 μm
0.1 mm
1 mm
1 cm
10 cm
1 m
10 m
100 m
Wavelength
Advantages Disadvantages
Visible
• High resolution• Large atmospheric
window
• Daytime only• Cloudless, clear
atmosphere
Infrared
• Day or night• Peak in Earth’s
emissions• Good resolution
• Cloudless, clear atmosphere
• Solar interference
Microwave (passive)
• Day or night• All weather
• Low resolution• Small signal
Microwave (Active)
• Day or night• All weather• High resolution
• Power demand