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49 Cards in this Set
- Front
- Back
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Digital images |
A numeric representation of 2D raster images |
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Color or (CIR) images have at least three bands: |
Blue Green Red |
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Converting analog images to digital |
Film images ---> computer |
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Linear array CCD |
scanning an image - scans one line of pixels at a time image ---> computer file light moves across image - light is reflected to sensor - sensor records high number for light areas, low number for dark areas |
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analog frame camera |
image represents an area on the ground "frame" |
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digital frame camera area array |
digital color images require 3 sets of sensors (red, green, blue) each sensor records 1 pixel image represents an area on the ground - acquired at one time |
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scanning mirror bases scanners |
scans across a line one pixel at a time depends on motion of platform to advance to next line - whisk broom MSS - LANDSAT - multi-spectral scanner 1972 |
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thematic mapper |
TM - Landsat bidirectional scanning |
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push broom linear array |
has a line of detectors- acquires a line at a time motion of platform to move the scanner along - no moving parts on instrument operational land imager (OLI) --> landsat 8 |
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imaging spectrometers |
collects many different wavelength bands ---> 200 |
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spectral resolution |
enough info in appropriate wavelengths? |
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spatial resolution |
how are the features you want to identify relative to the resolution of the imagery? (pixel size) |
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temporal resolution |
how often does the sensor record information in your area? |
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radiometric resolution |
sensitivity of sensor to differences in signal strength - 8-bit (256 different steps) |
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aerial photo single frames |
wide variety of purposes many different agencies historical imagery - mostly pre 1980s many different scales - mostly B&W panchromatic, some true color, some CIR scans of hard copies |
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NAPP |
National Aerial Photography Program began in 1987 - 5 year repeat, acquire imagery of whole US cloud free 20,000+ a.g.l (above ground level) 6 in focal length ---> 1:40,000 flown N to S through east and west halves 7.5 min. topo quads - 60% end lap |
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USDA FSA imagery |
farm service agency aerial photography field office film scans at $13/frame |
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georeferencing and rectification |
-georeferencing - real world coordinates attached to images |
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orthophotos |
an aerial photo processed to have the metric qualities of a map |
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processing |
mosaicking available tiled seamless |
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compression and file format |
zip gz tiff or tif - full resolution imagery compression built in jpg (jpeg or jfif) jpeg mrSID |
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digital imagery sources |
Earth explorer -orthophotos NAIP DOQ - digital orthophoto quadrangler state, county, regionals Ohio - OSIP |
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NAIP |
National Agricultural Imagery program 3 year cycle leaf-on imagery NRCS - geospatial data gateway |
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leaf pigments |
plant leaves have pigments in them that absorb light plants take in carbon dioxide & water ---> transform those to energy (sugars) using the energy from light ---> absorb light photosynthesis ---> chlorophyll low absorbance in green wavelengths---> reflects green pigments affect spectra in visible wavelengths - not much in IR wavelengths |
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leaf structure |
the structure of the cells in the leaf control the amount of NIR light that is reflected spongy mesophyll internal scattering of NIR - interfaces between cell wall & air - not connected to leaf pigment |
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biomass |
number of leaf layers affects the amount of NIR that's reflected |
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leaf moisture content |
how much water is in the leaf? Water absorbs energy in several parts of the middle IR - water absorbs in the water absorption bands -leaves reflect less light in IR when moist, more light when dry |
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color film |
object reflects: blue green red infrared blue green red **** |
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Color infrared film (CIR) |
object reflects: blue green red infrared **** blue green red |
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interpretation of vegetation features - types of plants |
deciduous (broad leaf) coniferous (needle leaf) - deciduous trees reflect more NIR light than coniferous trees shrubs herbaceous plants - tend to reflect more in NIR than deciduous |
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temporal aspects |
when (seasonally) plants will look like what on an image - i.e. leaf-on, leaf-off imagery, etc. |
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vegetation indices - simple ratio |
NIR reflectance/red reflectance - high numbers for vegetation - lower numbers for other cover types |
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vegetation indices - normalized difference vegetation index (NDVI) |
NIR - red/NIR + red - high values in vegetation lower values for other cover types |
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leaf - off imagery |
acquired before leaves are on trees - often in April |
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leaf- on imagery |
acquired during growing season - often july or august |
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three pathways associated with water |
surface water column bottom |
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diffuse reflection (water surface) |
many different directions rough surface |
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specular reflection (water surface) |
all reflected in one direction smooth surface (water tends to have a smooth surface at the scale of the wavelength of light) |
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reflection from water column |
infrared wavelengths ---> water absorbs a lot of incident energy in the IR wavelengths - middle IR especially - near IR as well - water does not reflect much IR light |
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water reflectance |
water is not a good reflector at any wavelength reflects more in shorter wavelengths than longer wavelengths in visible turbid water reflects more than clear water - turbid water does reflect in NIR - high suspended solids peak in red wave length - clear water has peak in blue or green |
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reflection from bottom of water body |
for clear water bodies, relatively shallow water will produce reflection from the bottom in blue wavelengths can get water depth penetration of 5 - 10 m in clear water |
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interpreting water features |
detection of water bodies -best done in IR wavelengths -water doesn't reflect -other things do |
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spectral characteristics of soil |
most soil curves show increasing reflectance with wavelength factors -texture -moisture content -organic matter content -iron oxide content |
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soil texture |
relative percentage of sand, silt, clay particles in soil particles of different sizes sand: largest silt: medium clay: very small as particle size decreases, spectral reflectance increases |
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moisture content |
how much water is there between soil particles? higher moisture content --> lower reflectance shape of curves shows water absorption bands for wetter soils |
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organic matter |
amount of plant derived material mixed in the soil high organic matter soils are dark low organic matter soils are light |
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iron oxides |
soils high in iron oxides are reddish in color |
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spectral characteristics: concrete & asphalt |
concrete - consistently bright asphalt - relatively dark, but can vary |
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land use/ land cover classification |
land use - residential, commercial, industrial land cover - the material that is covering the land - grass, trees, water, asphalt, bare soil... urban categories: -residential -commercial, service, institutional -industrial -transportation, utilities -open space |
