Aerial Photography and Remote Sensing Flashcards
What is Aerial Photography?
Uses of Aerial Photography
- Aerial Photography is a type of remote sensing method used to monitor land use. It is a method where photos are taken from above ground in an aircraft or satellites.
- There are to views:
- Oblique (easy to interpret)
- Vertical (Has a map like appearance)
- An infrared filter applied = improves contrast due to
plants - An Ultraviolet filter applied = improves contrast for rocks,
concrete, asphalt and metal
USES:
- Developed for warfare
- Important in discovering archaeological ruins
- important for forensic animation - help orientate viewer to accident scene
- Determine lines of sight, distances, positions, and established time lines for events
What energy does Aerial photography use?
- Light energy
- Uses passive, naturally occurring signal
Oblique View
- Require multiple angles (uncovers all angles)
- Any camera can be used
- For recognising terrain
Vertical View
- Professional camera required
- Presents a map looking view
- Smaller details than Oblique view
- For mapping
Aerial Photography - Interpretations:
SHADOWS:
- Due to height differences - e.g. ground collapse after
burial
- Best to use oblique view, towards sun, close to time of
sunset or sunrise
SOIL COLOUR VARIATIONS:
- Especially prominent after plowing
- Subsoils lighter than topsoils
- Damp soils darker than dry soils
VEGETATION PATTERNS:
- Depend on type of vegetation and stage of growing
season
- Positive crop marks = more plant growth
Looser soils = better for roots, depressions retain water,
corpse provides nutrients
- Negative crop marks = less plant growth
Tighter soils, no water retained, corpse provides PH
SNOW AND ICE:
- Enhances shadows
- Shows thermal properties of soil
Imaging Principles
Object = “real thing being seen” (size (X) distance (L))
Image = “The recorded thing”
Camera has a lens with a diameter (D) and focal length (F)
Image is recorded using light of wavelength (λ)
- The smallest object that can be seen = size of (Xmin)
Xmin = (L * λ) / D - Image in the recording medium = size of Y
Y = (X * F) / L
Level of detail
PHOTOGRAPHIC FILM:
- Divided into individual grains
- Each grain is either exposed (black) or unexposed (white)
- From 0.2 to 2μm in size for black and white film
- Approximately 10X larger for colour film
DIGITAL (CCD) DETECTOR:
- divided into individual pixels
- From 1 to 10 μm in size
- Each pixel has a range of greyscale intensities
-Image quality depends on signal to noise ratio
Thermal Imaging (Infrared)
- Passive technique - natural sources of IR radiation
- can be reflected from the sun or emitted from warm
items - Detects IR using special film or thermal scanner
- ONLY detects surface temperature
- Emissivity = amount of IR emitted (material dependent)
- Wavelength of emitted IR (dependent on temperature)
- Uses imaging equipment sensitive to infrared light
- When soil’s disturbed = different interactions with IR light
USES:
- Can be used to locate recent burials
- To indicate the number and location of fasteners
(relatively warm components, white colour or red)
-
Thermal Imaging (Infrared)
- Passive technique - natural sources of IR radiation
- can be reflected from the sun or emitted from warm
items - Detects IR using special film or thermal scanner
- Uses imaging equipment sensitive to infrared light
- When soil’s disturbed = different interactions with IR light
- ONLY detects surface temperature
- Emissivity = amount of IR emitted (material dependent)
- Wavelength of emitted IR (dependent on temperature)
- Decomposing bodies = warmer than surrounding soil
Uses of Thermal Imaging (Infrared)
- Can be used to locate recent burials
- To indicate the number and location of fasteners
(relatively warm components, white colour or red)
What affects Thermal Imaging (Infrared)
- Environmental Conditions:
- moisture
- dust
- wind
- sunlight
- Emitted infrared if best observed at night time
Remote Sensing
- Uses Infrared radiation and Radio waves
- longer wavelength than visible light
(pass through clouds)
lower resolution images
- longer wavelength than visible light
- Taking photos from an aircraft or satellite
- “Proximity” sensing = closer to round
- Advantages =
see a large area at once
get “Non- visible” information
Radar (Microwave)
- Plane with radar system used to map ground features
- SAR = synthetic aperture radar
- Active technique, based on the reflection of radar pulse
- Uses man-made signal
- Radio waves with Wavelength in cm are used
- Reflection is dependant on:
- soil type
- roughness
- moisture content
- disturbances due to burials may show up as anomalies
