Introduction to Remote Sensing

1. Introduction to Remote Sensing • History • EMR • EMS • Radiation Characteristics • Spectral Signatures

2. LANDSAT Imagery

3. 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. History • 1839 - first photograph • 1858 - first photo from a balloon • 1903 - first plane • 1909 first photo from a plane • 1903-4 -B/W infrared film • WW I and WW II • 1960 - space

5. Electromagnetic Radiation (EMR) • wavelength • frequency

6. Electromagnetic Radiation

7. 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. 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. 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. 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. 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. 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. Radiation

14. R/S Spectral Regions • Ultraviolet (UV) • Visible • Infrared (IR) • Microwave

15. R/S Spectral Regions

16. 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. R/S Spectral Regions

18. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. Solar and Terrestrial Radiation

30. 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. 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 300oK (80oF)

32. 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. 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. Radiation-Matter Interactions • EMR manifests itself only through its interactions with matter which can be in the form of; • a gas • a liquid • a solid

35. Radiation-Matter Interactions • When EMR strikes matter, EMR may be; • transmitted • reflected • scattered • absorbed

36. Radiation-Matter Interactions

37. 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. Transmission • Transmission is the process by which incident radiation passes through matter without measurable attenuation. The substance is thus transparent to the radiation.

39. 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. 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. 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. 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. 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. 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. 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. EMR - Atmosphere Interactions • Absorption bands define those areas where specific wavelengths are totally or partially blocked.

47. 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. 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. EMR - Atmosphere Interactions

50. Atmospheric Absorption and Transmission • Significant absorbers of EMR in the atmosphere; • oxygen • nitrogen • ozone • carbon dioxide • water vapor