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Visible-thermal-microwave

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Visible-thermal-microwave

## Visible-thermal-microwave

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1. GEOG 372 - Fall 2003Overview of Microwave Remote Sensing (Chapter 9 in Jensen)from Prof. Kasischke’s lecture October 6,2003

2. Visible-thermal-microwave

4. ‘ Speckle’

5. ‘Speckle’

6. Microwave energy is largely unaffected by the atmosphere, e.g., it has 100% transmission • Figure 1-18 from Elachi, C., Introduction to the Physics and Techniques of Remote Sensing, 413 pp., John Wiley & Sons, New York, 1987.

7. RADAR – Radio Detection and Ranging • Concept behind radars discovered in 1923 • RADARs systems invented in the 1930s • A high powered, radio transmitter/receiver system was developed that would transmit a signal that was reflected from a distant object, and then detected by the receiver • Thus, RADAR’s initial function was to detect and determine the range to a target

8. Fundamental Characteristics of Electromagnetic Energy • All EM energy travels at the speed of light (c = 3 x 108 m sec -1) in a vacuum in a wave form. • All EM energy has a wavelength -  - the distance between crests of successive waves. • All EM energy has a frequency – f - the number of wave crests that pass a stationary point per unit time.

9. Relationships between c, , & f c =  * f f = c /   = c / f

10. Band Frequency Wavelength (most common) X 8 to 12 GHz 2.5 to 4.0 cm (3.0 cm) C 4 to 8 GHz 4 to 8 cm (6.0) L 1 to 2 GHz 15 to 30 cm (24.0) P 0.3 to 1 GHz 30 to 100 cm (65 cm) Common Radar Bands

11. Key Components of a Radar System • Microwave Transmitter – electronic device used to generate the microwave EM energy transmitted by the radar. • Microwave Receiver – electronic device used to detect the microwave pulse that is reflected by the area being imaged by the radar. • Antenna – electronic component used through which microwave pulses are transmitted and received.

12. Measurements made with a simple radar • Range to the target • Intensity of the returned pulse • Azimuth resolution • Range resolution

15. Figure 9.4 from Jensen

17. Radar Foreshortening Radar look direction Radar foreshortening refers to the compression of the range dimension of an elevated object towards the direction the radar is looking

18. Radar Backscatter -  • Radar backscatter is the amount of energy received from the area of interest by a radar relative to the energy received from a metal target with a specified area • = energy from study area energy from calibrated target

19. Factors controlling surface scattering • Surface roughness • Surface dielectric constant

20. Surface Reflectance or Scattering • Specular reflection or scattering • Diffuse reflection or scattering

21. Specular Reflection or Scattering • Occurs from very smooth surfaces, where the height of features on the surface << wavelength of the incoming EM radiation

22. Diffuse Reflectors or Scatterers • Most surfaces are not smooth, and reflect incoming EM radiation in a variety of directions • These are called diffuse reflectors or scatterers

23. Radar backscattering is dependent on the relative height or roughness of the surface Figures from http://pds.jpl.nasa.gov/ mgddf/chap5/f5-4f.gif

24. Microwave scattering as a function of surface roughness is wavelength dependent

25. Microwave scattering is dependent on incidence angle Figure from http://pds.jpl.nasa.gov/ mgddf/chap5/f5-4f.gif

26. Radar sensing of forestsL-band (23 cm) is best

27. Microwave Scattering from a Water Surface Water has a dielectric constant of 80 • All scattering from water bodies in the Microwave region of the EM Spectrum is from surface scattering as no EM energy penetrates the water surface

28.  = 3 cm  = 24 cm

29. Smooth area – no wind  = 3 cm  = 24 cm

30. Factors controlling surface scattering • Surface roughness • Surface dielectric constant

31. Dielectric Constant • The dielectric constant is a measure of the electrical conductivity of a material • Degree of scattering by an object or surface is proportional to the dielectric constant of the material – •  ~ dielectric constant • To some degree, dielectric constants are dependent on microwave wavelength and polarization

32. Dielectric Constants of Common Materials • Soil – 3 to 6 • Vegetation – 1 to 3 • Water – 80 • For most terrestrial materials, the moisture content determines the strength of scattering of microwave energy

33. Radar cross section Stealth fighter = <0.02