RS Fundamentals Flashcards
Remote sensing
involves the use of instruments or sensors to capture the spectral and spatial relations of objects and materials observable from a distance
Components
- Energy source
- Radiation and atmosphere
- Interaction with target (changes nature)
- Energy recorded by sensor
- Transmission, reception, processing
- Interpretation and analysis
- Application of information
In RS main types of radiation processes are…
- emission
- reflection
- absorption
(ENERGY SOURCE) RS focuses on….
Measurement and information content of EM radiation
EM spectrum
-each interval makes up band or channel by:
colour
descriptive label
specified wavelengths
RS uses range of EM radiations
0.1 micrometers - 1m
UV radtiation
100-400 nm
Shortest wavelength used
-Induced fluorescence in the visible
Visible
0.4-0.7 micrometers
-Only visible wavelengths
(RGB)
Near Infrared
- 7-1.2 micrometers
- Just beyond visible
- Discriminated Green Vegetation well
Mid Infrared
- 2-8 micrometers
- Between NIR and thermal
Short Wave Infrared
- 2-3 micrometers
- Detects solar radiation
- Good for soil and veg moisture
3-8 micrometers
- Solar reflected and surface emitted
- Good for High temp sources
Thermal Infrared
8-14 micrometers
-Used to map surface Temp
Microwave
Penetrate cloud cover
-Detects Moisture
Passive energy source
- reflected energy from sun
- radiation emitted by objects
Active energy source
sensor generates own energy
Atmospheric interactions
-Interacts with incoming and outgoing EM radiation
-Gases (N, O, CO2, O3) + particles effects:
absorption
reflection & scattering
transmission
Atmospheric absorbers
Oxygen - filters UV below 0.1 micrometers
O3 - eliminates UV below 0.3 micrometers
Water vapour - strong absorber ~6 micrometers
CO2 - absorbs in TIR and from 2.5-4.5 micrometers
Scattering
redirection of EM radiation from original path due to gas or particles in atmosphere
-amount is dependent on wavelength, amount of particles and distance travelled
Rayleigh Scattering
particle «_space;wavelength
shorter wavelength = more scattering
all directions
Mie Scattering
particle >= wavelength
still spread out but more in direction of EM travel
Non Selective scattering
particle > wavelength
dominantly direction of EM travel
At surface radiation…
- is absorbed
- passes through target
- reflects
Spectral response
- signature dependent on degree of reflectance
- Texture dependent (in comparison to wavelength)
- smooth = reflection one direction
- rough = all direction
Land cover types do not always coincide with spectral reflectance curves due to variability of….
- solar elevation
- slope
- aspect
- atmosphere
- obstructions
Spectral reflectance signatures
- ) snow
- ) glacier ice
- ) rock
- ) water
- ) snow = high reflectance in visible
- ) glacier ice = lower in visible and near IR
- ) rock = high absorption
- ) water = high absorption
Water as target
Long wavelength = absorbed
Short wavelength = reflected
suspended sediment = better reflectivity
Resolution
Ability to discriminate information:
- spatial
- spectral
- radiometric
- temporal
Spatial Resolution
Min seperation at which objects appears independent and isolated
-Expressed a pixel size
Eg
MODIS - 1km
SPOT - 20m
IKONOS - 1m
When pixel size is smaller (greater spatial resolution)…
Pixel is more likely to be homogenous - closer to original value of target
Spectral Resolution
Number of bands provided by sensor and associated spectral bandwidths
Radiometric resolution
Indicated sensitivity of a sensor
For digital images the radiometric resolution = range of values coded by sensor
Temporal Resolution
Observation frequency
- cycle based on certain orbital characteristics and atmospheric conditions
Meteorological : 15-20 min
Landsat 5-7 : 16 days
Radar : 28 days
