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Aerial photographs
• "bird's-eye" view of the earth
• Photogrammetry = "the art or science of making measurements from aerial imagery"
Camera systems
K-25 WWII Recon Camera
High Quality Photographic
Systems and the Digital
Modular Camera
Uncorrected Aerial photographs
Uncorrected aerial photos have distortions
• radial distortion (due to lens curvature)
• geometric distortions (due to inconsistencies in the
attitude of the airplane)
• topographic distortions (due to relief)
Nadir
angle
Uses of aerial photgraphy
• Corrected images are often called orthoimages
• GIS applications: land use and land-cover classification, terrain analysis, natural resource mapping, image backdrops for maps, temporal-change analysis, etc...
Stereoscopy (three-dimensional imaging)
any technique capable of recordingthree-dimensional visual information or creating the illusion of depth in an image;
FUNDAMENTALS OF REMOTE SENSING
• Energy source• Atmospheric
interactions• Target interactions• Sensor records energy• Transmission to
receiving station• Interpretation• Application
The EM Spectrum10-1nm 1 nm 10-2m 10-1m 1 m 10 m 100 m 1 mm 1 cm 10 cm 1 m 102m
Gam
ma
Ray
s
X r
ays
Ultr
a-vi
olet
(UV
)
Vis
ible
(40
0 -
700n
m)
Nea
r In
frar
ed (
NIR
)
Infr
ared
(IR
)
Mic
row
aves
Wea
ther
rad
ar
Tel
evis
ion,
FM
rad
io
Sho
rt w
ave
radi
o
Vio
let
Blu
eG
ree
nY
ell
ow
Ora
ng
eR
ed
PIXELS: Minimum sampling area
One temperature brightness (Tb) value recorded per pixel
One temperature brightness (Tb) value recorded per pixel
Landsat Thematic Mapper (TM)
• 30 m spatial resolution
• 185 km FOV• Spectral resolution
– 0.45-0.52 μm– 0.52-0.60 μm– 0.63-0.69 μm– 0.76-0.90 μm– 1.55-1.75 μm– 10.4-12.5 μm– 2.08-2.35 μm
• 16 day repeat pass
EOS Terra MODIS
•Image Earth’s surface every 1 to 2 days
•36 spectral bands covering VIS, NIR, thermal
•1 km spatial resolution (29 bands)
•500 m spatial resolution (5 bands)
•250 m spatial resolution (2 bands)
•2330 km swath
Digital processing2 steps needed:
1) Georeferencing: assign real world coordinates
2) Orthorectification: remove all the distortions
Georeferencing
• Assigning real world coordinates
• Relating information (e.g., documents, datasets, maps, images) to geographic locations
• will correct displacements
Discrete georeferencing: through place names (i.e., toponyms)
and place codes (e.g., postal codes)
Geospatial referencing (e.g., longitude and latitude coordinates).
Discrete georeferencingor Geocoding
• The process of assigning a geographic location (e.g. latitude and longitude) to a geographic feature on the basis of its address.
• E.g. address matching
• mapquest.com
Geocoding method
• Based on a parcel centroid file that includes:
Street Name
Address
Nine-Digit ZIP Code
• Main source for geocoding base map data is TIGER (http://www.census.gov
/geog/www/tiger/)
Ground Control Points (GCPs)
• To georeference an image we need GCPs which are visible in the photographs,
• e.g road intersections, stone wall boundaries, building corners, and solitary trees.
• These points will be used to “tell” the GIS software:
where your image is in the world
how to correctly orient the photograph
correct for errors in photo-geometry.
Road curvesSquaresRivers
•24 GCPs – differentially corrected GPS (vertical and horizontal accuracy < 1m)
•Orthorectification
Ground Control Points (GCPs) collection
X
How many GCPs?
• Depends on the amount of distortion in your photograph and your desired level of accuracy
• mathematical formula applied to each pixel in the photo– first order (3 points min) does not distort, only shifts
– second order (6 points min)
– third order (9 points min) - distortions
Georeferencing to an image file
in ArcMap:
Spatial data (polygons, points, etc.) can be aligned to
an image file such as an historical map, satellite image, or aerial photograph.
Orthorectification
• mathematical process of removing the distortion caused by relief and the camera within a photograph so that the scale is uniform throughout the output image.
Distortion vs.displacement
• Distortion - Shift in the location of an object that changes the perspective characteristics of the photo.
• Displacement - shift in the location of an object in a photo caused by change in elevation.)