1. 10/23/2015 GEM 3366 1 Lecture 4 Content Electromagnetic wave

2. 10/23/2015 GEM 3366 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 10 8 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. 10/23/2015 GEM 3366 3 Measuring Light Light can be classified according to the length of the wave Gamma RaysUltravioletInfrared Microwave X-RayTV/Radio Wavelength The Electromagnetic Spectrum (EMS) Visible ˜ 0.4 micrometers ˜ 0.7

4. 10/23/2015 GEM 3366 4 Measuring Light: Bands Human eyes only ‘measure’ visible light Sensors can measure other portions of EMS Bands

5. 10/23/2015 GEM 3366 5 – –Electromagnetic Spectrum

6. 10/23/2015 GEM 3366 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. 10/23/2015 GEM 3366 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. 10/23/2015 GEM 3366 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. 10/23/2015 GEM 3366 9 Microwave portion – –Very low intensity – –Wavelength: 1mm to 1m – –Useful for penetrating hazy weather conditions

10. 10/23/2015 GEM 3366 10

11. 10/23/2015 GEM 3366 11 – –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

12. 10/23/2015 GEM 3366 12

13. 10/23/2015 GEM 3366 13 Sensors collect 2D images of the surface in a swath below the sensor Example: Landsat has a 185 km swath Swath

14. 10/23/2015 GEM 3366 14 Two types of images REMOTELY SENSED imagesContinuous data THEMATIC ImagesDiscrete data Measured Values (light) Quantitative Values only indicate class Qualitative

15. 10/23/2015 GEM 3366 15 Continuous data Two types: Panchromatic ( 1 Band/layer) Multispectral ( 2 or more Bands)

16. 10/23/2015 GEM 3366 16 Viewing continuous images Each band or layer is viewable as a separate image Thematic Mapper Band 1 Band 4 Band 5

17. 10/23/2015 GEM 3366 17 Blue Green Red NIR SWIR Part of spectrum Monitor color guns Viewing images Three bands are viewable simultaneously Band 4 Band 3 Band 2 Band 4 Band 5 Band 3 Band 1 Band 2 Band 3

18. 10/23/2015 GEM 3366 18 Band Combinations Features can become more obvious Vegetation Urban 2,3,1 (RGB)4,3,2 (RGB)4,5,3 (RGB)

19. GEM 3366 Image Geometric Correction Raw imagery has no reference to the ground Location in image only Defined by raster grid only

20. GEM 3366 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) Image Geometric Correction

21. GEM 3366 Ground Control Raw images need ground control 116 28 55.20 W, 33 00 22.43 N 116 47 27.20 W, 33 50 50.09 N 116 45 14.54 W, 33 43 05.65 N 116 28 07.20 W, 33 55 43.98 N Measured control points are used to correct entire image Resampling Method

22. 10/23/2015 GEM 3366 22 Discrete data (Thematic images) Deal with categorical information about an area Used and created by analytical operations Used to extract information from multispectral images

23. 10/23/2015 GEM 3366 23 Viewing thematic images Thematic images Each pixel contains a class value Each class value is associated with a specific color

24. 10/23/2015 GEM 3366 24 Viewing thematic images Each class can have associated attributes: Name, Color, Area etc. Exe…

25. 10/23/2015 GEM 3366 25 Vector Coverages Different means of representing features Raster Vector Polygons Lines Points

26. 10/23/2015 GEM 3366 26 Vector Coverages Vectors can also have attributes Vectors colored according to attributes

27. 10/23/2015 GEM 3366 27 … The End …