Photograph Vs Image?
Photograph: film or analog
Image: Digital
Air photos vs Maps
Air
- pictorial detail
- current
- sequence
- distortions
Maps
- better topographic representation
- annotations
- distortions
Black and white infrared
- only covers one spectral signature (one band)
- Only detects IR energy (infrared)
- higher contract between land and water
Black & White Panchromatic
- spectral signature is much larger (covers larger electromagnetic spectrum)
- contrast is less between water & land
Natural Colour
Spectral signature is blue, red & green
- appears as true color: closest to visible spectrum
False color Infrared
- Green, red, near infrared
Vegetation reflects infrared - Red plants, reflection increases or decreases based on health of plant species
- closest to what ultraviolet light would look like
3 types of air photos ( viewing angles)
- Vertical
- Low- Oblique
- High Oblique
what is a vertical photo angle
Vertical: optical axis of camera at nadir (directly down, perpendicular to the surface)
- can be used for photogrammetry
- scale is constant; creation of maps; directions can be measured
- stereoscopy is possible
What is an oblique photo angle
Oblique: Larger area covered than single vertical photo
- views are distorted
- typically a supplement to vertical photos
Low-Oblique: Camera Axis inclined about 30*
- only surface
High Oblique: Camera Axis about 60* form vertical
- sky, horizon, and surface
What annotations are on a analog or digital image
Analog:
- PP: principle point (directly under camera)
- greyscale: determines proper exposure
- fiducial mark (top of y axis/ camera)
- focal length
- clock
- lens serial number
- frame number
Digital: metadata found in Exchangeable Image File Format (EXIF)
What is a stereo pair
overlapping images:
A difference in perspective, created using multiple photos along a flightline enables stereo (3D) viewing.
What is the stereoscopic view
monocular vision vs depth perception
When brain relates 2 slightly different yet overlapping images to create depth perception
- we can use stereoscope on 2 similar images to create depth
In a stereo pair how much overlap must occur?
60% rule of thumb
What is stereoscopic parallax (parallactic angle)
The same object will appear on two or more of the photos, but from slightly different viewing angle = stereoscpoic paralax
- Parallactic angle: the optical axes of the eyes converge on a point
- Brain relates D with PA and defines depth perception
Why is stereoscopic viewing used in RS
- Exposure positions substitute for eye positions
- understand how shadows impact data sense
Why is Air photo interpretation essential
- information extraction from an image
- based on intended application (land use, glacial retreat)
- interpreter uses own knowledge + ability to recognize scene elements
what is a selective key (photo interpretation)
- select example that most closely corresponds to the object being identified
- Examples: industrial buildings, residential subdivisions, park (environments that are familiar or relatable)
What is an elimination key (photo interpretation)
- step process that leads to eliminatio of all items except those being identifies
- less common
8 Factors in Identifying features (photo interpretive elements)
- Shape
▪ Pattern
▪ Size
▪ Tone (color)
▪ Shadow
▪ Texture
▪ Association (site)
▪ Time
What is Shape
- form or configuration of an object
- regular, uniform shapes typically indicate human involvement
- example: crop circles, river meanders
- linear, curvilinear, circular, elliptical, radial, square, rectangular
- Curvilinear roads
What is Pattern
- Overall Spatial form of related features (groups)
- Spatial form or arrangement of objects
- Example: Row crops
- dendritic, random, systemic, radiating
What is Size
- measure of an objects surface area
- absolute: area, length, width, perimeter (knowledge of scale)
- Relative: small, medium large
What is Tone
- Color characteristics relative to other objects
- Used to identify features
- relative to characteristics of objects, film or sensor type, sunlight, and choice of display
- each feature will have a unique spectral signature
What is shadows
- can provide information about height shape, orientations
- qualitative context
- longer the shadow= higher the object
