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Introduction to GIS: Lecture #9 (Remote Sensing) Introduction to Remote Sensing History EMR EMS Radiation Characteristics Spectral Signatures.

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Presentation on theme: "Introduction to GIS: Lecture #9 (Remote Sensing) Introduction to Remote Sensing History EMR EMS Radiation Characteristics Spectral Signatures."— Presentation transcript:

1 Introduction to GIS: Lecture #9 (Remote Sensing) Introduction to Remote Sensing History EMR EMS Radiation Characteristics Spectral Signatures

2 Introduction to GIS: Lecture #9 (Remote Sensing) LANDSAT Imagery

3 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.

4 Introduction to GIS: Lecture #9 (Remote Sensing) History first photograph first photo from a balloon first plane 1909 first photo from a plane B/W infrared film WW I and WW II space

5 Introduction to GIS: Lecture #9 (Remote Sensing) Electromagnetic Radiation (EMR) wavelength frequency

6 Introduction to GIS: Lecture #9 (Remote Sensing) Electromagnetic Radiation

7 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.

8 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.

9 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).

10 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.

11 Introduction to GIS: Lecture #9 (Remote Sensing) EMS centimeter =.01 meters millimeter =.001 meters micrometer =.000,000,1 meters nanometer =.000,000,000,1 meters angstrom =.000,000,000,01 meters

12 Introduction to GIS: Lecture #9 (Remote Sensing) The EM Spectrum 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

13 Introduction to GIS: Lecture #9 (Remote Sensing) Radiation

14 Introduction to GIS: Lecture #9 (Remote Sensing) R/S Spectral Regions Ultraviolet (UV) Visible Infrared (IR) Microwave

15 Introduction to GIS: Lecture #9 (Remote Sensing) R/S Spectral Regions

16 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.

17 Introduction to GIS: Lecture #9 (Remote Sensing) R/S Spectral Regions

18 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).

19 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)

20 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.

21 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.

22 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

23 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.

24 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.

25 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.

26 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

27 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.

28 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.

29 Introduction to GIS: Lecture #9 (Remote Sensing) Solar and Terrestrial Radiation

30 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.

31 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 300 o K (80 o F)

32 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.

33 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.

34 Introduction to GIS: Lecture #9 (Remote Sensing) EMR manifests itself only through its interactions with matter which can be in the form of; a gas a liquid a solid Radiation-Matter Interactions

35 Introduction to GIS: Lecture #9 (Remote Sensing) Radiation-Matter Interactions When EMR strikes matter, EMR may be; transmitted reflected scattered absorbed

36 Introduction to GIS: Lecture #9 (Remote Sensing) Radiation-Matter Interactions

37 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.

38 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.

39 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.

40 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.

41 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 mirror- like surfaces are called specular reflectors. Specular reflection causes no change to either EMR velocity or wavelength.

42 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.

43 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.

44 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.

45 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.

46 Introduction to GIS: Lecture #9 (Remote Sensing) EMR - Atmosphere Interactions Absorption bands define those areas where specific wavelengths are totally or partially blocked.

47 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.

48 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.

49 Introduction to GIS: Lecture #9 (Remote Sensing) EMR - Atmosphere Interactions

50 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

51 Introduction to GIS: Lecture #9 (Remote Sensing) Atmospheric Absorption and Transmission

52 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

53 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.

54 Introduction to GIS: Lecture #9 (Remote Sensing) Atmospheric Scattering Important scattering agents include; gas molecules suspended particulates clouds

55 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

56 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.

57 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.

58 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

59 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.

60 Introduction to GIS: Lecture #9 (Remote Sensing) Non-selective scattering Important nonscattering agents include; larger Mie particles water droplets ice crystals

61 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.

62 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.

63 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.

64 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.

65 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.

66 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.

67 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.

68 Introduction to GIS: Lecture #9 (Remote Sensing) EMR - Surface Interactions

69 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.

70 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.

71 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.

72 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.

73 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.

74 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.

75 Introduction to GIS: Lecture #9 (Remote Sensing) Spectral Signatures

76 Introduction to GIS: Lecture #9 (Remote Sensing) LANDSAT Imagery


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