1. Energy Sources and Radiation Principles

2. Energy and Radiation Forms of electromagnetic energy: visible light
heat
ultraviolet and X-rays
radio waves

3. Two Components of EM Radiation
The waves are characterized by electrical and magnetic fields.
The vibration of these fields is perpendicular to the direction of the wave.
Electrical field (E): varies in magnitude in a direction perpendicular to the direction of propagation
Magnetic field (M): at right angle to the electrical field, is propagated in phase with the electrical field

4. Components of EM Radiation

5. Three Properties of EM Energy
Wavelength (l)
Frequency (n)
Amplitude

6. Wavelength (l)
The linear distance between two successive wave crests or troughs.
It is measured in meters (m), nanometers (nm)(10-9 m) or micrometers (10-6 m)

7. Frequency (n)
The number of wave crests or troughs that pass a fixed point per unit time.
Measure units: hertz (cycle per second)  

8. Amplitude The height of each peak
Measured as watts per square meter (energy level)

9. Speed of EM
Electromagnetic energy is traveling at the velocity of light:
velocity of light (c) = frequency (v)* wavelength ()
Among the three properties, wavelength is the most commonly used in the field of remote sensing

10. Wavelength/Frequency
Low
Long
Short
High

11. Electromagnetic spectrum
In RS, electromagnetic waves are categorized by their wavelength location within the electromagnetic spectrum.
The total range of wavelengths is commonly referred to as the Electromagnetic spectrum

12. Major Divisions of EM Spectrum
Ultraviolet spectrum: micrometer (m)
Visible portion: 0.4 – 0.7 m
Blue: m
Green: m
Red: m

13. Major Divisions of EM Spectrum
Infrared spectrum (IR):
        - near infrared: m         - mid infrared:  m         - thermal infrared:  beyond 3 – 14 m , emitted from the earth
Microwave spectrum: 1mm - 1m

14. Electromagnetic spectrum
The sun produces a full spectrum of electromagnetic radiation

15. Electromagnetic (EM) Spectrum

16. Energy and Radiation
Common RS sensors operate in visible, IR, or microwave portions.
Only thermal IR energy is directly related to the sensation of heat.

17. Energy and Radiation
Using particle theory (instead of wave theory), the electromagnetic radiation is composed of many discrete units called photons or quanta.
The energy of a quantum is:
Q=hv
Where Q is in Joules (J), h is Planck’s constant (J sec), and v is the frequency.

18. Energy and Radiation
Combining the previous two equations (c=v and Q=hv): Q=hc/
i.e. the longer the wavelength of a quantum, the lower its energy content.

19. Energy and Radiation

20. Wavelength and frequency
Four different types of electromagnetic waves, illustration
The inverse relationship between wavelength and frequency

21. Wavelength and frequency

22. Energy and Radiation
All matter at temperatures above 0 K (-273 C) continuously emits electromagnetic radiation.
The amount of energy radiated by any object is a function of the surface temperature, emissivity, and the wavelength
There are no blackbodies is nature. Blackbody is a matter that is capable of absorbing and re-emitting all electromagnetic energy that it receives.
All natural objects are graybodies, they emit a fraction of their
maximum possible blackbody radiation at a given
temperature T. This fraction is called emissivity (ε)
ε = E/Eb
Where E is actual energy and Eb is the blackbody
energy at a given temperature.

23. Blackbody Radiation Curves

24. Wien’s Displacement Law
Notice that the peak of the
Blackbody curve shirts to shorter wavelengths as
temperature increases
This peak represents the wavelength of maximum emittance (λmax)

25. Wien’s Displacement Law
As the temperature of an object increases, the total amount of radiant energy (area under the curve, in W/m2) increases and the radiant energy peak shifts to shorter wavelengths.
To determine this peak wavelength (λmax) for a blackbody:
λmax = A/T
where A is a constant (2898 μm K) and T is the temperature in Kelvins.

26. Developments from Planck’s Law Stefan-Boltzmann Law
The area under the Planck curve represents the total energy emitted by an object
at a given temperature
The Stefan-Boltzmann law
gives this energy for a blackbody

27. Developments from Planck’s Law Stefan-Boltzmann Law
The Stefan-Boltzmann law is derived by integrating the
Planck function with respect to wavelength:
M = σT4
σ is called the Stefan-
Boltzmann constant.
σ = x 10-8
Energy or the radiant flux (rate of flow of EM energy)

28. Active and passive remote sensing
Active systems provide their own source of energy (e.g. radar and laser)
Active sensors emit a controlled beam of energy to the surface and measure the amount of energy reflected back to the sensor
The main advantage of active sensor systems is that they can be operated day and night, have a controlled illuminating signal, and are typically not affected by the atmosphere.
Passive systems depends on an external source of energy, usually the sun, and sometimes the Earth itself (e.g. photographs, multispectral scanners).
Passive sensor systems based on reflection of the Sun’s energy can work only during daytime.
Passive sensor systems that measure the longer wavelengths do not depend on the sun as a source of illumination and can be operated at any time.

29. Passive Remote Sensing

30. Active Remote Sensing

31. Energy interactions in the atmosphere
The composition of the atmosphere influences both the incoming solar radiation and the outgoing terrestrial radiation
The radiance (the energy reflected by the surface) received at a satellite is a result of electromagnetic radiation that undergoes several processes which are wavelength dependent

32. Scattering
- Scattering is the unpredictable diffusion of radiation by particles in the atmosphere
Scattering is a function of the ratio of the particle diameter of the material doing the scattering to the wavelength of the incident radiation
Types of scattering
1- Rayleigh Mie 3- Nonselective

33. Rayleigh scattering
Common when radiation interacts with atmospheric molecules and other tiny particles that are much smaller in diameter than the wavelength of the interacting radiation
Rayleigh scattering is proportional to the inverse of the wavelength raised to the fourth power: shorter wavelengths are scattered more than longer wavelengths
At daytime, the sun rays travel the shortest distance through the atmosphere- Blue sky
At sunrise and sunset, the sun travel a longer distance through the Earth’s atmosphere before they reach the surface- The sky appears orange or red.
Tends to dominate under most atmospheric conditions

34. Mie scattering
It exists when atmosphere particle diameters is similar in size to the wavelength of the incoming radiation.
- Water vapor and dust are major causes of Mie scattering
Mie scattering tends to influence longer wavelengths.
It is restricted to the lower atmosphere where large particles are more abundant, and dominates under overcast could conditions.

35. Nonselective scattering
The diameters of the particles causing scatter are much larger than the wavelengths of the energy being sensed.
Water droplets (5-100 μm) and larger dust particles
Non-selective scattering is independent of wavelength, with all wavelengths scattered about equally (A could appears white)
It scatters all visible and near to mid IR wavelengths.

36. Absorption
- The process by which incident radiant energy is retained by a substance
- Energy converted to another form- light to heat
Water vapor, carbon dioxide, and ozone all absorb electromagnetic energy

37. Transmission, reflection, scattering, and absorption

38. Atmospheric windows (transmission bands )
-The wavelength ranges in which the atmosphere is particularly transmissive
-The dominant windows in the atmosphere are the visible and radio frequency regions
-X-Rays and UV are very strongly absorbed and Gamma Rays and IR are somewhat less strongly absorbed.

39. Atmospheric windows

40. Basic interactions between electromagnetic energy and an earth surface feature
The interaction of incoming radiation with surface features depends on both the spectral reflectance properties of the surface materials and the surface smoothness relative to the radiation wavelength
The percentages of energy reflected, absorbed, and transmitted vary for different earth features, depending on their material type and condition.
- The percentages of energy reflected, absorbed, and transmitted vary at different wavelengths.

41. Basic interactions between electromagnetic energy and an earth surface feature

42. Specular versus diffuse reflectance
- Specular reflectors are flat surfaces that manifest mirrolike reflections. The angle of reflection equals the angle of incident
Diffuse (or Lambertian) reflectors are rough surfaces that reflect uniformly in all the directions
Diffuse contain spectral information on the color of the reflecting surface, whereas specular reflections do not.
In remote sensing we are often interested in measuring the diffuse reflectance of objects.

43. Specular and diffuse reflectors
Specular reflection
Diffuse reflection

44. Energy interactions with earth features
Albedo - Spectral reflectance R(): the average amount of incident radiation reflected by an object at some wavelength interval
R() = ER() / EI() x 100
Where
ER() = reflected radiant energy
EI() = incident radiant energy

45. Identification of Surface Materials Based on Spectral Reflectance

46. Spectra of vegetation Absorption is dominant process in visible
Scattering is dominant process in near infrared
Water absorption is increasingly important with increasing wavelength in the infrared.

47. Spectra of soil
What are the important properties of a soil in an RS image
-Soil texture (proportion of sand/silt/clay)
-Soil moisture content
-Organic matter content
-Mineral contents, including iron-oxide and carbonates
-Surface roughness

48. Dry soil spectrum
Increasing reflectance with increasing wavelength through the visible, near and mid infrared portions of the spectrum

49. Soil moisture and texture
Clays hold more water more ‘tightly’ than sand.
Thus, clay spectra display more prominent water absorption bands than sand spectra

50. Soil moisture and texture

51. Soil Organic Matter
Organic matter is a strong absorber of EMR, so more organic matter leads to darker soils (lower reflectance curves).

52. Iron Oxide
Recall that iron oxide causes a charge transfer absorption in the UV, blue and green wavelengths, and a crystal field absorption in the NIR (850 to 900 nm). Also, scattering in the red is higher than soils without iron oxide, leading to a red color.

53. Surface Roughness Smooth surface appears black.
Smooth soil surfaces tend to be clayey or silty, often are moist and may contain strong absorbers such as organic content and iron oxide.
Rough surface scatters EMR and thus appears bright.

54. Spectra of water Reflectance peak shifts toward
longer wavelengths as more
suspended sediment is added

55. Data acquisition and image interpretation

56. Data acquisition and interpretation
Image is used for any pictorial representation of image data
Photograph: Images that were detected as well as recorded on film

57. Digital Image bands (z) rows (y) columns (x)72 80 84 92 97 94 85 78 75 81 70 74 93 88 79 71 61 67 76 82 90 87 77 89
103 96 44 59
110
105 56 39 51 83 91 95
101
100
104 58 43
106 86 41 40 65 45 32 69 38 64 53 72 80 84 92 97 94 85 78 75 81 70 74 93 88 79 71 61 67 76 82 90 87 77 89
103 96 44 59
110
105 56 39 51 83 91 95
101
100
104 58 43
106 86 41 40 65 45 32 69 38 64 53 72 80 84 92 97 94 85 78 75 81 70 74 93 88 79 71 61 67 76 82 90 87 77 89
103 96 44 59
110
105 56 39 51 83 91 95
101
100
104 58 43
106 86 41 40 65 45 32 69 38 64 53
rows (y)
columns (x)
Image size: The no. of rows (or lines) and no. of columns (or samples) in one scene

58. Digital Image data

59. Digital Images 72 80 84 92 97 94 85 78 75 81 70 74 93 88 79 71 61 67 76 82 90 87 77 89
103 96 44 59
110
105 56 39 51 83 91 95
101
100
104 58 43
106 86 41 40 65 45 32 69 38 64 53
Digital numbers (DNs) typically range from 0 to 255; 0 to 511; 0 to 1023, etc.
These ranges are binary scales: 28=256; 29=512; 210=1024.

60. Different kinds of image
Panchromatic image
True-color image
False-color image

61. Panchromatic image
If airborne cameras use black/white film or satellite sensors use a single band, it produces panchromatic image (gray scale image)

62. Color composite Color primaries: RGB (Red, Green, Blue)
Many colors are formed by combining color primaries in various proportions
Same principles apply to producing color images taken from airborne cameras or satellite sensors

63. Greyscale vs. RGB Greyscale is typically used to display a single band
RGB (“Red”, “Green”, “Blue”) images can display 3 bands, corresponding to the red, green and blue phosphors on a monitor.

64. True color and false color images
True color image- the color of the image is the same as the color of the object imaged.
A false color image is one in which the R,G, and B values do not correspond to the true colors of red, green and blue.
The most commonly seen false-color images display the very-near infrared as red, red as green, and green as blue.
For instance, different types of vegetation might appear as blue, red, green or yellow. Intuitively, vegetation would appear green.
Vegetation appear red in this color composite

65. True color and false color images

66. Describing Sensors Spatial resolution Spectral resolution
Temporal resolution
Radiometric resolution

67. Spatial Resolution

68. Spatial Resolution
Spatial resolution is a measure of the smallest object that can be resolved by the sensor
In aerial photography, it is the minimum separation between two objects for which the images appear separate.
Airborne and some spaceborne systems: cm – m resolution
Most spaceborne systems: 10’s of m to kilometers

69. Spatial resolution
Spatial: The size of the smallest possible feature that can be detected.
Pixel size is the area covered by one pixel on the ground
In a digital image, the resolution is limited by the pixel size, i.e. the smallest resolvable object cannot be smaller than the pixel size.
Fine or high resolution image refers to one with a small resolution size. Fine details can be seen in a high resolution image.
Coarse or low resolution image is one with a large resolution size, i.e. only coarse features can be observed in the image.
Aerial photo has higher resolution
The image resolution and pixel size are not equivalent.

70. Spatial Resolution

71. Spatial resolution A low resolution MODIS scene (1km)
A very high resolution image acquired
by the IKONOS satellite (1m)

72. Spectral Resolution
The number, wavelength position and width of spectral bands a sensor has
A band is a region of the EMR to which a set of detectors are sensitive.
Multi-spectral sensors have a few, wide bands (several spectral bands)
Hyper-spectral sensors have a lot of narrow bands (hundreds of spectral bands)

73. Spectral Resolution
Multi-spectral
hyper-spectral

74. What is Radiometric Resolution?
The number of brightness levels the sensor can record

75. Radiometric Resolution
Radiometric resolution refers to the number of possible brightness values (or light levels) in each band of data, and is determined by the number of bits into which the recorded energy is divided.
It described the sensitivity of the sensor to variations in brightness.
Typically, 8,10, or 12 are used for representing the radiometric levels
In 8-bit data, the brightness values can range from 0 to 255 for each pixel (256 total possible values). In 7-bit data, the values range from 0 to 127, or half as many possible values.

76. Radiometric Resolution
8-bit radiometric resolution
28 = 256 levels
3-bit radiometric resolution
23 = 8 levels

77. Radiometric Resolution
2-bit = 4 radiance levels
8-bit = 256 radiance levels
The finer the radiometric resolution of a sensor, the more sensitive it is to detecting small differences in reflected or emitted energy.

78. Radiometric Resolution
2-bit
4 gray levels
8-bit
256 gray levels

79. Temporal resolution
Temporal resolution is a description of how often a sensor can obtain imagery of a particular area of interest, determined by the repeat cycle of its orbit.
For example, the Landsat satellite revisits an area every 16 days as it orbits the Earth, while the SPOT satellite can image an area every 1 to 4 days due to off-nadir viewing.

80. Temporal resolution
How frequent a given location on the earth surface can be imaged by imaging system.
For satellite image, it can be regular (satellites are orbiting the earth in regular time interval)

81. Geosynchronous Orbit
A satellite in geosynchronous orbit circles the earth once each day.
The time it takes for a satellite to orbit the earth is called its period.
To stay over the same spot on earth, a geostationary satellite also has to be directly above the equator.
Otherwise, from the earth the satellite would appear to move in a north-south line every day.

82. Sun-Synchronous Orbit
Because the valid comparison of images of a given location acquired on different dates depends on the similarity of the illumination conditions, the orbital plane must also form a constant angle relative to the sun direction.
This is achieved by ensuring that the satellite overflies any given point at the same local time, which in turn requires that the orbit be sun-synchronous
The satellite crossed the equator at approximately the same local sun time (9:42) every day

83. Earth Resource Satellites Operating in the Optical Spectrum
Landsat
SPOT
Meteorological Satellites
NOAA satellites
GOES satellites
Ocean Monitoring Satellites
Radar Satellites
Seasat
ERS-1
JERS-1
Radarsat

84. Introduction
Satellite systems operating within the optical spectrum ( m): UV, visible, near-, mid-, and thermal IR wavelengths
Landsat and SPOT
Higher resolution, contemporary programs (IKONOS, QuickBird)

85. Earth history of space imaging
Cameras on rockets (Germany 1891, 1907)
: beginning of space RS with small cameras aboard V-2 rockets (NM, USA)
Meteorological satellites (initial application) TIROS-1 (1960)
Corona, a military space imaging reconnaissance program ( ).

86. Earth history of space imaging
Manned space programs:
Mercury, Gemini, Apollo
Alan Shepard (1961): Made a 15-min suborbital Mercury flight on which 150 excellent photographs were taken
John Glenn (1962): Made 3 historic orbits around the earth and took 48 color photographs during Mercury mission MA-6
Gemini GT-4: geological application
Other geographic & oceanographic phenomena

87. Earth history of space imaging
Apollo 9: multispectral orbital photography for earth resource studies
1973: Skylab: Earth Resources Experiment Package (EREP)
1975: US-USSR Apollo-Soyuz Test Project (ASTP) hand-held cameras, disappointing results

88. Landsat Satellite Program Overview
Earth Resources Technology Satellites (ERTS) program (1967): a planned sequence of six satellites
In 1975, ERTS was renamed by NASA “Landsat”

89. Landsat Program
During the experimental Landsat phase, imagery was disseminated by Earth Resources Observation System (EROS) Data Center at Sioux Falls, SD.
Satellites were operated by NASA and USGS was handling the data distribution.

90. Landsat Program
Gradually, NOAA took over and the Landsat program operation was transferred to a commercial firm (Earth Observation Satellite Company – EOSAT).
Landsat-7 operation reverted to the government; EROS Data Center is the primary receiving station, processing and distributing the data.

91. Landsat Program
Landsat-1,-2,-3 images are catalogued according to their location within the Worldwide Reference System (WRS), by specifying:
a path (each orbit within a cycle)
a row (individual nominal sensor frame centers)
a date

92. Landsat Program

93. Landsat Program
E.g. the WRS has 251 paths for Landsat –1, -2,-3 (number of orbits to cover the Earth in 18 days).
Paths are numbered from 001 to 251, E to W, row 60 coincides with the equator.

94. ERTS-1 (Landsat-1) Launched by a rocket on 7/23/1972
Operated until 1/6/1978
The first unmanned satellite specifically designed to acquire data about earth resources on a systematic, repetitive, medium resolution, multispectral basis
43 US states & 36 countries

95. Landsat Satellite Program Overview
Landsats carried combinations of 5 types of sensors:
Return Beam Vidicon (RBV) camera systems
Multispectral Scanner (MSS) systems
Thematic Mapper (TM)
Enhanced Thematic Mapper (ETM)
Enhanced Thematic Mapper Plus (ETM+)

96. Landsat 1-3 orbital characteristics
Sun-synchronous orbits: The satellite crossed the equator at approximately the same local sun time (9:42) every day
Lunched into circular orbits at 900 km
Near-polar orbits travels northwards on one side of the earth and then toward the southern pole on the second half of its orbit, 14 times a day
Passing same point every (coverage repetition)
Sensors aboard imaged only 185 km swath
Globe coverage every 18 days (20 times/year)