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Lecture 4 Content

Lecture 4 Content. Electromagnetic wave. Electromagnetic wave Visible light, radio waves, heat, ultraviolet, and X-rays are all forms of electromagnetic energy All forms of electromagnetic energy travels at the speed of light which is 3 x 10 8 m/sec

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Lecture 4 Content

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  1. Lecture 4 Content Electromagnetic wave

  2. Electromagnetic wave • Visible light, radio waves, heat, ultraviolet, and X-rays are all forms of electromagnetic energy • All forms of electromagnetic energy travels at the speed of light which is 3 x 108 m/sec • The type of energy being detected is characterized by its position in the electromagnetic spectrum • The spectrum is commonly divided into units of wavelengths measured in micrometers (μm) which is one millionth of a meter

  3. Wavelength Visible ˜ 0.7 ˜ 0.4 micrometers Measuring Light • Light can be classified according to the length of the wave The Electromagnetic Spectrum (EMS) Microwave Gamma Rays X-Ray Ultraviolet Infrared TV/Radio

  4. Measuring Light: Bands • Human eyes only ‘measure’ visible light • Sensors can measure other portions of EMS Bands

  5. Electromagnetic Spectrum

  6. Electromagnetic spectrum characteristics • Visible portion: • Region to which the human eye is sensitive • Extremely narrow range of wavelengths • Wavelength: 0.4 μm to 0.7 μm ( the blue and red regions) • The ultra-violet region has the shorter wavelengths next to the visible blue region

  7. Infra-red portion • Cannot be seen directly with the human eye • Wavelength: 0.7 μm to 0.8 μm • Longer than the red rays in the visible portion • Useful for penetrating hazy weather conditions

  8. Thermal infra-red portion • Cannot be detected by the human eye nor by photographic film • Wavelength: 0.8 μm to 14 μm • Electronic detectors cooled by liquid nitrogen are used to measure the energy emitted at these wavelengths

  9. Microwave portion • Very low intensity • Wavelength: 1mm to 1m • Useful for penetrating hazy weather conditions

  10. Emission of energy from a blackbody • Area under the curve represents the total amount of energy emitted • Sun’s highest energy levels are emitted at the wavelength 0.5 μm • Atmospheric effects • Atmospheric windows are the regions of the spectrum that are used for remote sensing • The systems operating in wavelengths longer that the visible range makes use of such windows for which the atmosphere has relatively high transparency

  11. Swath • Sensors collect 2D images of the surface in a swath below the sensor • Example: Landsat has a 185 km swath

  12. Two types of images • REMOTELY SENSED images Continuous data • Measured Values (light) • Quantitative • THEMATIC Images Discrete data • Values only indicate class • Qualitative

  13. Multispectral ( 2 or more Bands) • Panchromatic ( 1 Band/layer) Continuous data • Two types:

  14. Thematic Mapper Band 1 Band 4 Band 5 Viewing continuous images • Each band or layer is viewable as a separate image

  15. Monitor color guns Part of spectrum Band 4 Band 1 Band 4 Blue Green Band 3 Band 5 Band 2 Red NIR Band 2 Band 3 Band 3 SWIR Viewing images • Three bands are viewable simultaneously

  16. Urban Vegetation Band Combinations • Features can become more obvious 4,5,3 (RGB) 2,3,1 (RGB) 4,3,2 (RGB)

  17. Image Geometric Correction • Raw imagery has no reference to the ground Location in image only Defined by raster grid only

  18. Image Geometric Correction • Correction is the process of giving an image a Real World coordinate system 116 41 52.20 W, 33 50 03.23 N (Latitude, Longitude)

  19. 116 28 55.20 W, 33 00 22.43 N 116 47 27.20 W, 33 50 50.09 N Resampling Method 116 28 07.20 W, 33 55 43.98 N 116 45 14.54 W, 33 43 05.65 N Ground Control • Raw images need ground control • Measured control points are used to correct entire image

  20. Discrete data (Thematic images) • Deal with categorical information about an area • Used and created by analytical operations • Used to extract information from multispectral images

  21. Viewing thematic images • Thematic images • Each pixel contains a class value • Each class value is associated with a specific color

  22. Viewing thematic images • Each class can have associated attributes: • Name, Color, Area etc. Exe…

  23. Vector Raster Polygons Lines Points Vector Coverages • Different means of representing features

  24. Vectors colored according to attributes Vector Coverages • Vectors can also have attributes

  25. … The End …

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