Aerial photography and satellite imagery as data input

GEOG 4103, Feb 20th

Adina Racoviteanu

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...

Black and white aerial photography

Color aerial photography

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

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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.

Georeferencing terrestrial photography

GCP

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.)

A sports stadium in downtown Toronto before and after rigorous orthorectificationImagery courtesy of DigitalGlobe

Orthorectification