Remote Sensing week 4
Remote Sensing week 4 GEOG 2107
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This 4 page Class Notes was uploaded by Ivana Szwejkowski on Monday September 26, 2016. The Class Notes belongs to GEOG 2107 at George Washington University taught by Engstrom, R in Fall 2015. Since its upload, it has received 3 views. For similar materials see Intro to Remote Sensing in Geography at George Washington University.
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Date Created: 09/26/16
Remote Sensing Week 4 Review: Interpretation Process - Human vs. Automated Electro-magnetic Radiation (EMR) - Amplitude - Wavelength- Wave theory - Frequency - Energy- quantum theory (Relationship, Planck’s law; Frequency X Planck’s constant) Energy Levels - Stefan’s Boltzman Law - Sun- visible - Earth- heat - EMR Transmission Atmospheric Windows - Portions of the Spectrum that transmits EMR effectively Atmospheric Constituents - Water droplets & ice crystels - Gas Molecules - Aerosols (particles suspended in the atmosphere) Scattering - Re-direction - No change in other properties - 3 primary types 1. Rayleigh (molecular) Similar in all directions Interacts with short wavelengths; Nitrogen Athunt of scattering is inversely proportional to wavelength rasied to the 4 power Example: Blue light .4 um; 1/.4^4 = 39.06 Red light .7 um; 1/.7^4= 4.1649 39/4=9 Occur in upper 4.5 km of the atmosphere Accounts for blue sky & red sunset 2. Mie Scattering (Aerosol) Direction dependent Particles with diameter about equal to wavelength Dust, Pollutants, volvanic eruptions, smoke Urban areas better to picture after it rains Effects longer wavelengths Lower 4.5 km of atmosphere 3. Non-selective Scatter Diameter of particles is much larger than lambda (10 X) Cloud water droplets/ ice crystals Affects all wavelengths, hence, “non-selective” Scattering Effects - Reduces direct illumination from sun and creates diffuse illumination - Scatter can occur anywhere in info flow - Can be corrected through a filter Path Radiance - Radiation scattered into the sensor from the atmosphere - Mostly shorter wavelengths Contrast Reduction - Atmospheric effects can reduce image contrast Absorption -Radiant Energy is taken in by matter and converted into other forms of energy -atmospheric gases are selective absorbers with reference wavelength Radiant Energy / Radiant Flux - Radiant Energy (Q lambda): Capacity of radiation within a spectral band to do work (J) - Radiant Flux (phi) : time rate of energy flow onto, off of, or through a surface Watts (Joules per second) - Understanding flux is the purpose of Remote sensing Surface energy partitioning - Absorption - Transmission - Reflection Radiation budget equation - Dimensionless ratios of the radiant flux absorbed, transmitted, or reflected to the total incident radiant flux - Conservation: energy cannot be created or destroyed - Absorbed, transmitted, or reflected; Sum=1 Irradiance + Exitance over an area Properties affecting Target Radiance EMR Target/Surface type Sensor angle Interaction- determines target radiance detected by the sensor Spectral signature Concept - Describes spectral reflectance of a target at different wavelengths of EMR - Spectral reflectance curve- graphs reflectance response as a function of wavelength - Key to separating and identifying objects - Selection of optimum Surface Type: Specular-incidence energy will leave surface at an angle equal and opposite to the incident energy Diffuse- uniform reflection of incidence energy in all directions Review: 9/21/16 Surface energy partitioning Reflection, absorption, transmission Energy Radiant Flux (energy from the sun), Irradiance (radiant flux that’s coming into an area; Watts/ meter^2) , Radiant existence (wavelengths coming off of object), Radiance(angle to sun) Reflectance (percent) Spectral signature Surface Type Surface Type Specular reflectance: Water (angle of incidence) Diffuse Reflectance: Photograph Geometry High oblique and Low oblique Info that can be obtained: Vertical air photos Scale of photography (panchromatic is grey scale) Object height Object length Area Perimeter Grayscale tone or color of an object Photographic elements- Annotation Date/ time Firm/series Coordinates Scale Altitude Focal length and altitude together can calculate scale Fiducials- PP; principle point Minimum of four markers on photo Nadir- point directly below aircraft For a true vertical image: Nadir=PP < 3 degrees from Nadir 60 percent overlap; stereoscopic
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