10/23/2015 GEM Lecture 4 Content Electromagnetic wave

10/23/2015 GEM 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

10/23/2015 GEM 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

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

10/23/2015 GEM – –Electromagnetic Spectrum

10/23/2015 GEM – –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

10/23/2015 GEM 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

10/23/2015 GEM 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

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

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10/23/2015 GEM – –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

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

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

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

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

10/23/2015 GEM 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

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

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

GEM 3366 Correction is the process of giving an image a Real World coordinate system W, N (Latitude, Longitude) Image Geometric Correction

GEM 3366 Ground Control Raw images need ground control W, N W, N W, N W, N Measured control points are used to correct entire image Resampling Method

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

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

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

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

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

10/23/2015 GEM … The End …