outline: definition of remote sensing components of system electromagnetic radiation nature of...
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Outline:Outline: definition of remote sensing
components of system
electromagnetic radiation
nature of an image
light interaction with atmosphere and surface
types of remote sensors
Remote Sensing
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science and art of obtaining information about something from a distance.
analysis of collected data to obtain information about the objects, areas or phenomenon under investigation.
Remote Sensing
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Components of System
propagation through the atmosphere
energy interactions with earth surface features
transmission through the atmosphere
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Data Analysis:Data Analysis:
examining the data using various viewing and interpretation devices to analyze pictorial data and/or a computer to analyze digital sensor data (i.e. GIS).
Components of System
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Energy Sources:Energy Sources:
energy available from sun is described by electromagnetic spectrum
Electromagnetic Radiation
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Wavelength - distance from one wave crest to another.
Frequency - number of wave crests passing a fixed point in a given period of time. Measured in hertz (1 cycle per second)
Electromagnetic Radiation
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Electromagnetic RadiationAmplitude - height of each peak. Measured as spectral irradiance
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Ultraviolet Radiation - 0.4 micrometers
not much is done with UV for remote sensing since these shorter wavelengths are easily scattered by the atmosphere
Electromagnetic Radiation
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Visible Radiation
BLUE (.4-.5 micrometers)
GREEN (.5-.6 micrometers)
RED (.6-.73 micrometers)
Electromagnetic Radiation
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Infrared Radiation - .72 - 15 micrometers
1. Near Infrared - reflected, can be recorded on film
2. Mid Infrared - reflected, can be detected using electro-optical sensors.
3. Thermal Infrared - emitted, can only be detected using electro-optical sensors
Electromagnetic Radiation
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Microwave Radiation - radar sensors, wavelengths range from 1mm to 1m
Electromagnetic Radiation
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most systems rely on the sun to generate all the EM energy needed to image terrestrial surfaces - passive sensors.
other sensors generate their own energy, called active sensors, transmits that energy in a certain direction and records the portion reflected back by features within the signal path
Electromagnetic Radiation
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atmospheric modification of incoming and outgoing EM radiation includes scattering, refraction and absorption
Light Interaction with Atmosphere
Scattering
redirection of light by particles
can be in any direction
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General Effects of Scattering
causes skylight (allows us to see in shadow)
forces image to record the brightness of the atmosphere in addition to the target.
directs reflected light away from the sensor, decreasing spatial detail (fuzzy images)
tends to make dark objects lighter and light objects darker (reduces contrast)
Light Interaction with Atmosphere
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Refraction
bending of light when it passes through two media
degrades spectral signatures on hot- humid days
Light Interaction with Atmosphere
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Absorption
mostly caused by three atmospheric gases: ozone, carbon dioxide and water vapour
Light Interaction with Atmosphere
no attenuation attenuation
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Reflection
the bouncing of electromagnetic energy from a surface
type of reflection is dependent on the size of the surface irregularities relative to the incident wavelength.
Light Interaction with Surface
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1. Specular Reflectance
light is reflected in a single direction - 'mirror' reflection
specular reflectance helps and hinders remote sensing
Light Interaction with Surface
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2. Diffuse/Lambertian Reflectance
energy is reflected equally in all directions
many natural surfaces act as a diffuse reflector to some extent.
Light Interaction with Surface
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image – model target features described through the use of spectral reflectance
software and hardware specially designed to analyze these images give us the ability to see a pictorial rendition of targets.
images that we see on a computer screen are made up of picture elements called pixels.
Nature of the Image
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Pixel - picture element having both spatial and spectral properties.
the spatial property defines the "on ground" height and width.
the spectral property defines the intensity of spectral response for a cell in a particular band
Nature of the image
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Nature of the Image
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when only one band of the EM spectrum is sensed, the output device (colour monitor) renders the pixels in shades of grey
Nature of the Image
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multispectral sensors detect light reflectance in more than one or two bands of the EM spectrum. these bands represent different data - when combined into the red, green, blue guns of a color monitor, they form different colors
Nature of the Image
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multispectral image is composed of 'n' rows and 'n' columns of pixels in each of three or more spectral bands
Nature of the Image
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most common, versatile and economic form of remote sensing
spectral range 0.3 to 0.9 mm (visible portion of spectrum).
photogrammetry is the science, art and technology of obtaining reliable measurements, maps, other derived products from photographs.
Aerial Photography/Airphoto
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AADVANTAGES OF DVANTAGES OF AAERIAL ERIAL
PPHOTOGRAPHYHOTOGRAPHY
Five Basic Advantages
Improved vantage point
Capability to stop action
Permanent recording
Broadened spectral sensitivity
Increased spatial resolution and geometric fidelity
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camera produces a large-format 23x23cm photo
contain high precision/well calibrated lenses that minimize spatial distortions
motor-driven film advances – 60% overlap between successive exposures
Aerial Photography/Airphoto
panchromatic, black-and-white, true-colour film
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Aerial Photography/Airphoto Grey scale step wedge
Notes
Altimeter
Fiducial marks
Clock
Lens serial number
Focal length
Frame number
Mission name and date
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Airphoto – Saudi Arabia
Aerial Photography/Airphoto
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advantages: improves vantage point, capability to stop action, permanent recording, broadened spectral sensitivity, increased spatial resolution.
disadvantages: can’t get at elevation, not appropriate for urban areas (tall buildings block information)
applications: land use/land cover mapping, geologic and soil mapping, agricultural application, forest applications, wildlife ecology, etc.
Aerial Photography/Airphoto
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currently there are 2777 satellites orbiting the earth (US – 878)
multi-purpose:
scientific
defense
communications
global positioning system (GPS)
Satellite Remote Sensors
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geostationary orbiting satellites are those that remain stationary relative to a point on the surface of the earth
i.e. communications and meteorological satellites
Satellite Remote Sensors
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Satellite Remote Sensors
polar-orbiting satellites are those in which the position of the satellite’s orbital plane is kept constant relative to the sun.
i.e. Landsat satellite series
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Passive Remote Sensing
measure natural radiation emitted by target or/and radiation energy from other sources reflected from the target
examples: passive microwave radiometers, LandSat, SPOT
AACTIVE VS CTIVE VS PPASSIVE ASSIVE RREMOTE EMOTE
SSENSINGENSING
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AACTIVE VS CTIVE VS PPASSIVE ASSIVE RREMOTE EMOTE
SSENSINGENSING
Active Remote Sensing
transmit their own signal and measure the energy that is reflected or scattered back from the target
advantages: ability to “see” regardless of time of day or season; use wavelengths not part of solar spectrum; better control of the way target is illuminated
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sensors that operate in the microwave portion of the spectrum
advantages: capable of penetrating atmosphere under virtually all conditions, different view of the environment.
disadvantage: radar instruments have a hard time identifying water bodies because the wavelength is much longer than the general character of the surface roughness
applications: sea ice and snow, geologic features, ocean bottom contours, other planets.
Microwave Sensors
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Microwave radiometer – narrow-beam antenna attached to a scanning device
soil moisture, water content of snow, geologic strata
Synthetic Aperture Radar – shorter antenna that emits and receives returned energy from ground objects
day/night, clouds/cloud free operation
Microwave Sensors
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RADARSAT
launched in November 1995
developed by Canada to monitor environmental change and the planet’s natural resources
heart is synthetic aperture radar (SAR) – microwave instrument that sends pulsed signals to earth and processes the received reflected pulses.
Microwave Sensors
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First RADARSAT Image
Microwave Sensors
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ERS-2 Vancouver Island
Microwave Sensors
European SAR
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sensors that operate in the optical portion of spectrum, which extends from approximately 0.3 to 14 mm.
can do more with these data because it is numbers.
look at differences in colors
look at differences over time
applications: meteorological, ocean monitoring (i.e. chlorophyll absorption).
Optical Sensors
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show how much energy from the sun was being reflected or emitted off the Earth's surface when the image was taken.
clear water reflects little radiation, so it looks black.
pavement and bare ground reflect a lot of radiation, so they look bright.
urban areas usually look light blue-grey.
vegetation absorbs visible light but reflects infrared, so it looks red
Optical Sensors
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Optical image of Montreal area during ice storm of 1998. Icesnow and clouds appear as various colors of white, vegetationis green.
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GOES - Geostationary Operational Environmental Satellite (Visible to NIR, Thermal)
DMSP - Defense Meterological Satellite Program 600 m resolution (Visible to NIR, Thermal), urban heat island studies
Nimbus - CZCS - coastal zone color scanner, 825 m spatial resolution
AVHRR - Advanced Very High Resolution Radiometer – meteorological satellite (visible, NIR, thermal)
Optical Sensors
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AVHRR - Advanced Very High Resolution Radiometer – meteorological satellite (visible, NIR, thermal)
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Channel Wavelength Primary Use1 0.58 - 0.68 Daytime cloud/surface mapping
2 0.725 - 1.10 Surface water delineation, ice and snow melt
3A 1.58 - 1.64 Snow / ice discrimination (NOAA K,L,M)
3 3.55 - 3.93 Sea surface temperature, nighttime cloud mapping
4 10.30 - 11.30 Sea surface temperature, day and night cloud mapping
5 11.50 - 12.50 Sea surface temperature, day and night cloud mapping
AVHRR Channels
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LANDSAT - visible, NIR spectral bands (Landsats 1,2,3), and MIR and Thermal (Landsats 4 and 5)
Multispectral scanner - 4 spectral bands – Green, Red, and 2 NIR
Thematic mapper - 7 spectral bands – Blue/Green, Green, Red, NIR, MIR, MIR, Thermal
Optical Sensors
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LANDSAT MSS image - Grand Canyon
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LANDSAT TM image - southwestern Utah and Southern Nevada
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SPOT Image of the WTC Fires