newoct-elements of visual interpretation_1
TRANSCRIPT
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Overview
Remote sensing overview Value and limitations of working with
paper images
Visual interpretation methods Hands-on image exploration and
interpretation
Discussion of applications whereprinted images can be usedeffectively
Wrap-up
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How can satellite images helpconservation practitioners?
Observe land cover, boundaries, threats,damage, topography
Monitor change in forest cover, range condition,land use
Classify into vegetation and land usecategories, habitats
Measure areas, distances, height/elevation Detect fires, resource use violations
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Highlights of Earth Remote Sensing
Before 1972 - primarily aerial andsatellite photographs
1972 - First Landsat satellite launched
1978 - SPOT satellite launched
1988 - Indian Remote Sensing Satellitelaunched
1995 - Radarsat launched
1999 - IKONOS satellite launched andNASA launched Terra satellite
Today many new satellite and airborneinstruments are being developed andlaunched
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An image is made up of individual elements called pixelsthat are arranged in a grid of rows and columns.
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The sensor acquires several images (bands) at once, eachrecording a specific color or range of colors. When viewed,each individual band looks like a black and white
photograph
Landsat band 2- (wavelength range = 0.52-0.60 m = blue light)
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Electromagnetic Spectrum
Source: http://observe.ivv.nasa.gov/nasa/education/reference/reflect/ir.html
For each band the intensity of energy for a specificrange of wavelengths (colors) is measured
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Spectral signatures
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RGB Band Composite
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Pixel color and brightness isdetermined by the pixel value
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Certain bands or band combinations are better than others for identifyingspecific land cover features.
Landsat TM Red= band 3, Green =band 2, Blue = band 1
Landsat TM Red= band 4, Green =band 5, Blue = band 4
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Landsat ETM+ band 1 (0.45-0.52 m, blue-green)
Penetrates water betterthan the other bands so itis often the band ofchoice for aquaticecosystems
Used to monitor sedimentin water, mapping coralreefs, and water depth
The noisiest of theLandsat bands since short
wavelength blue light isscattered more than theother bands
Rarely used for "prettypicture" type images
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Landsat ETM+ band 2 (0.52-0.60 m, green)
Similar qualities to band 1but not as noisy.
Matches the wavelength
for the color green.
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Landsat ETM+ band3 (0.63-0.69 m, red)
Since vegetation absorbsnearly all red light (it issometimes called thechlorophyll absorptionband) this band can beuseful for distinguishingbetween vegetation andsoil and in monitoringvegetation health
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Landsat ETM+ band 4 (0.76-0.90 m, near infrared)
Since water absorbsnearly all light at thiswavelength water bodiesappear very dark. This
contrasts with brightreflectance for soil andvegetation so it is a goodband for defining thewater/land interface
Sensitive to vegetationcover
Less affected byatmospheric
contamination
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Landsat ETM+ band 5 (1.55-1.75 m, mid-infrared)
Very sensitive tomoisture and istherefore used tomonitor vegetation
water stress and soilmoisture. Useful to differentiate
between clouds andsnow
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Landsat ETM+ band 6 (10.40-12.50 m, thermal infrared)
Measures surfacetemperature.
Geological applications
Differentiate clouds frombright soils since cloudstend to be very cold
The resolution is twice ascourse as the other bands
(60 m instead of 30 m)
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Landsat ETM+ band 7 (2.08-2.35 m mid-infrared)
Can detect high surfacetemperatures
Also used for vegetation
moisture althoughgenerally band 5 isgenerally preferred forthat application
Commonly used ingeology
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Landsat ETM+ bands 3,2,1Penetrates shallow water andshows submerged shelf, water
turbidity
Landsat ETM+ bands 4,3,2Peak chlorophyll, land/waterboundary, urban areas
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Landsat ETM+ bands 4,5,3Land/water boundary,Vegetation type and condition,
soil moisture
Landsat ETM+ bands 7,4,2Moisture content in vegetationand soils, geological mapping,
vegetation mapping
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MODIS (500m)Composited using imageryacquired from JuneSeptember 2001
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Landsat ETM+ (30m) - 2 April 2002
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ASTER (15m) - 8 November 2003
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IKONOS (1m)29 April 2002
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IKONOS zoomed
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Advantages of using paper imagery
No need for a computer or fancyequipment
Inexpensive to createVery portable and easy to carry in the field
Easy to show other people and often a
more effective communication tool Looks nice on the wall
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Limitations of using paper imagery
Ancillary data obscures image data
Not possible to zoom into the image
Not possible to change the imageenhancement
Can not easily overlay other data layers
Generally more difficult to locate oneselfon the image since GPS tracking is notpossible
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Visual Interpretation Skills
How to read a satellite image
Wh t d d t i t t
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What do you need to interpretremotely sensed imagery?
Familiarity with the specific area or similarareas
Basic interpretation skills Image prints that are of sufficient quality
Projection grid marks on the image are helpful
to locate oneself on the image using a GPS Equipment to protect the imagery if working in
the field
Tools to transcribe information onto the image
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Basic Elements of Visual
Interpretation Tone (color)
Size and shape
Texture and pattern
Relative and absolute location
Shadows
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Tone and Color
Variations in tone andcolor results in all of theother visual elements
When looking at a image
photo we associatespecific tones toparticular features
Tones change when we
enhance an image orwhen we change theband combination of acolor image
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Size and Shape
Rectangular featuresoften indicate humaninfluence such asagriculture
Size and shapeinformation greatlyinfluenced by imageresolution
Knowing the scale of theimage helps to convertfeature dimensions onthe image to actualdimensions
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Texture and Pattern
Varies with imageresolution
Often noted by
roughness orsmoothness
Influenced byshadows
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Relative and Absolute Location
The location of afeature narrows thelist of possible cover
types Relative location
particularly useful todetermine land use
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Shadows
Often considered acontaminant but can bevery useful to identifyfeatures on an image
Helpful to accentuate
relief Shadow effects change
throughout the day andthroughout the year
Shadows can give anindication to the size of aparticular feature
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Exercises
Purpose: Give you a change to do some of whatwe just talked about
After the break we will: Explore different satellite images
Identify features on printed satellite images
Relate features in the image with features in a
photograph Draw lines around features we can see in the satellite
images
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Supplies that will be used in class
Imagery (Landsat ETM+ ASTER, Corona,IKONOS, ground photo)
Topographic map Transparencies
Masking tape
Black marker Cotton
Alcohol
i
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Exercises
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Discussion
Questions, additions, and clarifications
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Wrap Up
What have we learned? Where satellite images come from and what
they are made of
How to interpret images Methods for using images as an aid to
conservation management
After this class Find some images for your area (use
handout)
Play with them using some of the techniques
di d