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 recording three-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 Spectrum nm 1 nm  m  m 1  m 10  m 100  m 1 mm 1 cm 10 cm 1 m 10 2 m Gamma Rays X rays Ultra-violet(UV) Visible ( nm) Near Infrared (NIR) Infrared (IR) Microwaves Weather radar Television, FM radio Short wave radio Violet Blue Green Yellow Orange Red

PIXELS: Minimum sampling area One temperature brightness (T b ) value recorded per pixel

Landsat Thematic Mapper (TM) 30 m spatial resolution 185 km FOV Spectral resolution – μm – μm – μm – μm – μm – μm – 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 processing 2 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 georeferencing or 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 (

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 curves Squares Rivers 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 orthorectification Imagery courtesy of DigitalGlobe Orthorectification