newoct-elements of visual interpretation_1

8/13/2019 NewOCT-Elements of Visual Interpretation_1

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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

newoct-elements of visual interpretation_1

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