Remote Sensing Midterm Study Guide
Remote Sensing Midterm Study Guide GEOG 2107
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This 9 page Study Guide was uploaded by Ivana Szwejkowski on Wednesday September 28, 2016. The Study Guide belongs to GEOG 2107 at George Washington University taught by Engstrom, R in Fall 2015. Since its upload, it has received 2 views. For similar materials see Intro to Remote Sensing in Geography at George Washington University.
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Date Created: 09/28/16
Remote Sensing Definition “the measurement or acquisition of information of some property of an object or phenomenon, by a recording device that is not in physical or intimate contact with the object or phenomenon under study -Lack of contact with object Information flow Sun, Atmosphere, Target , atmosphere, sensor, image, interpretation, application Tool Remote sensing is a tool or technique similar to mathematics. Using sensors to measure the amount of electromagnetic radiation (EMR) exiting an object or geographic area from a distance and then extracting valuable information from the data using mathematically and statistically based algorithms is a scientific activity. It functions in harmony with other spatial data-collection techniques or tools of the mapping sciences, including cartography and geographic information systems (GIS) Links with other disciplines Relationships of the Mapping Sciences as they relate to Mathematics and Logic, and the Physical, Biological, and Social Sciences ( remote sensing, GIS, Cartograpy/surveying) In-situ vs. remote sensing Both attempt to observe and/or measure objects and phenomena In-situ: Physical contact (interaction), Instruments for direct measure, Ground-reference vs. “Ground truth”. Sensing: Data is collected by sensor not in contact with the object • How remote? No single standard, Platforms for sensory operate at multiple different levels, near surface to global scale data collection. • Cranes, Balloons, Aircraft, Satellite, UAVs • Data collected: image(2-D); Application Areas • Land use / land cover mapping • Photogrammetry (obtaining reliable measurements) • Natural resource inventory and mapping • Water quality monitoring • Physical/biological oceanographic mapping • Atmospheric monitoring • Advantages & disadvantages: A: different perspective, obtain data for large areas, in single acquisition efficient, obtain data for inaccessible areas, doesn’t affect/ interact with phenomena of interest. D: Accuracy and consistency, Artifacts( processing errors ), scale related ( image is too coarse/detailed, or moving between scales: in-situ + image data), high initial outlays for equipment and training. Remote Sensing process: Statement of problem (or data collection requirements, Data Collection, Image Processing (Data-to-information process), Information Presentation. • Four Resolutions • Spatial – spatial resolution (size of the field of view i.e. 10mX10m • Temporal – temporal resolution (frequency of image acquisition) • Spectral - the number and size of spectral regions the sensor records data in, e.g. blue, green, red, near Infrared, thermal infrared, microwave (radar) • Resolution-Pixel Size? for an object to be detected its size should be 2x the pixel size. Spatial -Grain and Extant? Grain: smallest object distinguishable on image, detail, similar to pixel sixe. Extent: area covered my image, small grain size=small area covered(small extent) Temporal- Aircraft: potentially high temporal resolution - Satellite: fixed orbit, systematic collection, pointable sensors Spectral – Broadband: few, relatively broad bands - Hyperspectral: many, relatively narrow bands • Radiometric- Measured in terms of the number of energy levels discriminated - 2^n where n=number of bits, • Image Interpretation- Act of examining images for the purpose of identifying and measuring objects and phenomena, and judging their significance • Art & Science • Detection, Identification, Measurement, Problem solving Interpreter requirements: Color, stereo vision Human vs. Automated approaches -humans generally utilize higher order elements of interpretation; context, size, shape; qualitative. Computers; accurate tone, less biased, perhaps less accurate Elements of Image Interpretation • Tone/color- amount of energy depends on reflectance of object and sensitivity of sensor. Black and white(panchromatic) or color(specific wavelength bands) intensity(brightness), hue(intensity of wavelength), and saturation(purity of color relative to grey). • Texture – rough or smooth; scale dependent • Size – relative or absolute if scale of imagery is known or feature size is known. • Shape – natural tendencies vs cultural tendencies • Pattern – combines micro elements of repetition for recognition of characteristic phenomena • Shadow – indicates absence of direct illumination, hinders analysis if object of interest is obscured, can aid analysis ( enhances terrain relief, determine height, shape) • Height-Oblique image data can provide relative measure of height, but absolute measurements are difficult because scale varies • Context- site and association • Interpretation Process: Human vs. Automated- general to specific • Electro-Magnetic Radiation (EMR)- link between object and sensor • Amplitude- height of wave peak, related to amount of energy carried by wave • Wavelength- distance from peak to peak, measured in micrometers 10^6 • – Wave Theory; • Frequency – measured in Hertz (Hz) number of wave forms passing through a certain point per unit time • Energy – frequency= speed of light/ wavelength • – Quantum Theory-Interaction of EMR with matter; absorption and emission, photons • Relationship; inverse relationship btw frequency and wavelength • Planck’s Law ; energy of a photon. Q = hv, energy of a quantum in Joules = planks constant x frequency of EMR • Energy levels • Stefan Boltzman Law: M = σT4 describes emitted radiation from a blackbody as a function of temperature M= total emitted energy = SB constant Temperature (K) • Wien’s Law: Used to identify wavelength of maximum energy emission • λ max= K/T • Peak EMR wavelengths • Energy coming from the sun &earth • Atmospheric interactions- scattering and absorption Atmospheric effects Transmission- energy propagated directly through the atmosphere Atmospheric Window- portions of the spectrum that transmit EMR effectively Constituents: responsible for absorption and scattering: water droplets/ ice crystals, gas molecules, Aerosols Scattering-redirection of energy, no change in other properties Typesof scattering: Rayleigh(molecular)-particle diameter shorter than wavelength ie gas molecules, wavelength^4 power, upper 4.5 km of atmosphere. Mie(aerosol)- particle diameter equal to wavelength, dust, pollutents, occurs in lower 2.5 km of atmosphere, direction of scattering depends on shape size, and distribution of particles Non-selective- diameter of particles is much larger than wavelength, cloud water vapor/ ice cryselt, affects all wavelengths Effects- reduces direct illumination, increases diffuse illumination, sensor can use filter, may add or reduce signal of sensor. Absorption- Radiant energy is taken in by matter and Converted into other forms of energy, Oxygen, Nitrogen, Ozone, Carbon Dioxide, Water Vapor, atmosphere is selective absorption Regions- ozone- ultraviolet radiation, water vapor- infrared, carbon dioxide- thermal infrared Surface energy partitioning -Reflection, absorption, transmission Radiant flux (time rate of energy flow onto, off of or through a surface (Watts), Irradiance (radiant flux incident upon a surface per unit of space), Radiant Exitance (radiant flux leaving a surface per unit) , Radiance(radiant flux leaving a specific projected source area in a given condition within a specific solid angle) Reflectance- Target Reflector: Specular , Diffuse Sun/sensor angle Air photos – stereoscopic model 60 percent overlap Oblique photography 20-30 percent overlap Vertical, high and low oblique Annotation Fiducials Principle point- conjugate principal points Nadir Optical Axis Height & Focal length Scale= f/H Similar triangles f – focal length H –height of aircraft above the ground Impact of elevation : flat terrain, versus variable terrain. Scale= f/(H’-h) • Air photos- orthographic projection vs. central projection • Relief displacement- radial distance Differences in relative elevation of objects in photo • camera increasingly sees the side of an object the further from nadir point.hough viewed from the same point, so • -magnitude- higher than datum (lean outward) , lower than datum(lean inward) • Photogrammetry- art and science of making accurate measurements form an aerial photography • Calculating height- h=d(relief displacement)x ((H(height above ground level)/r(distance from principle point)) • Relief displacement • Shadow- h=LxTan(a) • Stereoscopic viewing • Parallax • Alignment • Parallax principle • Calculating height h0= (H’-h)x dp/(P+dp) • Remote Sensing • Platforms • Ground based • Lighter than air • UAV • Platforms • UAV • Aircraft • Types • Advantages/Disadvantages • NAPP – color IR, B&W • Camera systems • F/stop, aperature, shutter speed, field of view, • hardware • Satellites- range determined by orbit; sun synchronous or geostationary • Orbit • Advantages/Disadvantages
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