Remote Sensing and ImageProcessing: 3
Dr. Hassan J. Eghbali
Back to the process....
•What sort of parametersare of interest?
•Variables describingEarth system....
Dr. Hassan J. Eghbali
EO and theEarth“System”
External forcing
Hydrosphere
Atmosphere
Geosphere
Cryosphere
Biosphere
Dr. Hassan J. Eghbali
Example biophysical variables
Dr. Hassan J. Eghbali
Example biophysical variables
Good discussion of spectral information extraction:
http://dynamo.ecn.purdue.edu/~landgreb/Principles.pdf
Dr. Hassan J. Eghbali
Remote Sensing Examples
Dr. Hassan J. Eghbali
Information extraction process
Imageinterpretation
•Tone, colour,stereo parallax
•Size, shape,texture,pattern, fractaldimension
•Height/shadow
•Site,association
Primaryelements
Spatialarrangements
Secondaryelements
Context
Analogueimageprocessing
•Multi:
•spectral, spatial,temporal, angular,scale, disciplinary
•Visualisation
•Ancillary info.:field and labmeasurements,literature etc.
Presentationof information
•Multi:
•spectral, spatial,temporal, angular,scale, disciplinary
•Statistical/rule-based patterns
•Hyperspectral
•Modelling andsimulation
Dr. Hassan J. Eghbali
Example: Vegetation canopy modelling
•Develop detailed 3Dmodels
•Simulate canopyscattering behaviour
•Compare withobservations
Dr. Hassan J. Eghbali
•Core principles of electromagnetic radiation (EMR)
–solar radiation
–blackbody concept and radiation laws
•EMR and remote sensing
–wave and particle models of radiation
–regions of EM spectrum
–interaction with atmosphere
–interaction with surface
•Measurement of radiation
Electromagnetic (EM) Spectrum
Dr. Hassan J. Eghbali
•This is what we measure in remote sensing
•Terms, units, definitions
•Provide basis for understanding type ofinformation that can be retrieved
•Why we choose given regions of the EMspectrum in which to make measurements
EM spectrum: so what?
Dr. Hassan J. Eghbali
Remote sensing process: recap
Dr. Hassan J. Eghbali
•Note various paths
–Source to sensor direct?
–Source to surface to sensor
–Sensor can also be source
•RADAR, LiDAR, SONAR
•i.e. “active” remote sensing
•Reflected and emitted components
–What do these mean?
•Several components of final signal captured at sensor
Remote sensing process: recap
Dr. Hassan J. Eghbali
•Conduction
–transfer of molecular kinetic (motion) energy due to contact
–heat energy moves from T1 to T2 where T1 > T2
•Convection
–movement of hot material from one place to another
–e.g. Hot air rises
•Radiation
–results whenever an electrical charge is accelerated
–propagates via EM waves, through vacuum & over long distanceshence of interest for remote sensing
Energy transport
Dr. Hassan J. Eghbali
EM Spectrum
•EM Spectrum
•Continuous range of EM radiation
•From very short wavelengths (<300x10-9m)
•high energy
•To very long wavelengths (cm, m, km)
•low energy
•Energy is related to wavelength (and hence frequency)
Dr. Hassan J. Eghbali
•Energy radiated from sun (or active sensor)
•Energy 1/wavelength (1/)
–shorter (higher f) == higher energy
–longer (lower f) == lower energy
Dr. Hassan J. Eghbali
Units
•EM wavelength is m, but various prefixes
•cm (10-2m)
•mm (10-3m)
•micron or micrometer, m (10-6m)
•Angstrom, Å (10-8m, used by astronomers mainly)
•nanometer, nm (10-9)
•f is waves/second or Hertz (Hz)
•NB can also use wavenumber, k = 1/ i.e. m-1
Dr. Hassan J. Eghbali
EM Spectrum
•We will see how energy is related to frequency, f (and hence inversely proportionalto wavelength, )
•When radiation passes from one medium to another, speed of light (c) and change,hence f stays the same
Dr. Hassan J. Eghbali
Electromagnetic spectrum: visible
•Visible part - very smallpart
–from visible blue (shorter)
–to visible red (longer )
–~0.4 to ~0.7m
Violet: 0.4 - 0.446 m
Blue: 0.446 - 0.500 m
Green: 0.500 - 0.578 m
Yellow: 0.578 - 0.592 m
Orange: 0.592 - 0.620 m
Red: 0.620 - 0.7 m
Dr. Hassan J. Eghbali
Electromagnetic spectrum: IR
•Longer wavelengths (sub-mm)
•Lower energy than visible
•Arbitrary cutoff
•IR regions covers
–reflective (shortwave IR,SWIR)
–and emissive (longwave orthermal IR, TIR)
–region just longer than visibleknown as near-IR, NIR.
Dr. Hassan J. Eghbali
Electromagnetic spectrum: microwave
•Longer wavelength again
–RADAR
–mm to cm
–various bands used byRADAR instruments
–long so low energy,hence need to useown energy source(active wave)
Dr. Hassan J. Eghbali
Electromagnetic spectrum
•Interaction with the atmosphere
–transmission NOT even across the spectrum
–need to choose bands carefully to coincide with regions wheretransmission high (atmospheric windows – see later)
Dr. Hassan J. Eghbali
“Blackbody” concept
•All objects above absolute zero (0 K or -273° C)radiate EM energy (due to vibration of atoms)
•We can use concept of a perfect blackbody
•Absorbs and re-radiates all radiation incident upon it atmaximum possible rate per unit area (Wm-2), at eachwavelength, , for a given temperature T (in K)
•No real object is blackbody but it is v. useful assumption
•Energy from a blackbody?
Dr. Hassan J. Eghbali
Stefan-Boltzmann Law
•Total emitted radiation from a blackbody, M, in Wm-2,described by Stefan-Boltzmann Law
•Where T is temperature of the object in K; and = isStefan-Boltzmann constant = 5.6697x10-8 Wm-2K-4
•So energy T4 and as T so does M
•Tsun 6000K M,sun 73.5 MWm-2
•TEarth 300K M , Earth 460 Wm-2
Dr. Hassan J. Eghbali
Stefan-Boltzmann Law
Dr. Hassan J. Eghbali
Stefan-Boltzmann Law
•Note that peak of sun’s energy around 0.5 m
•negligible after 4-6m
•Peak of Earth’s radiant energy around 10 m
•negligible before ~ 4m
•Total energy in each case is area under curve
Dr. Hassan J. Eghbali
Peak of emitted radiation: Wien’s Law
•Wien deduced from thermodynamic principles thatenergy per unit wavelength E() is function of T and
•At what m is maximum radiant energy emitted?
•Comparing blackbodies at different T, note mT isconstant, k = 2897mK i.e. m = k/T
•m, sun = 0.48m
•m, Earth = 9.66m
Dr. Hassan J. Eghbali
Wien’s Law
•AKA Wien’sDisplacement Law
•Increase(displacement) in mas T reduces
•Straight line in log-log space
Increasing
Dr. Hassan J. Eghbali
Planck’s Law of blackbody radiation
•Planck was able to explain energy spectrum of blackbody
•Based on quantum theory rather than classical mechanics
•dE()/d gives constant of Wien’s Law
•E() over all results in Stefan-Boltzmann relation
•Blackbody energy function of , and T
Dr. Hassan J. Eghbali
Planck’s Law
•Explains/predicts shape of blackbody curve
•Use to predict how much energy lies between given
•Crucial for remote sensing
Dr. Hassan J. Eghbali
Consequences of Planck’s Law
•Chlorophyll a,b absorption spectra
•Photosynthetic pigments
•Driver of (nearly) all life on Earth!
•Source of all fossil fuel
•Allows us to explain radiantenergy distribution of anyobject (e.g. sun)
•Predict at what peak energyis emitted and so choose ourspectral bands accordingly
Dr. Hassan J. Eghbali
Recap
•Physical properties we might measure
–E.g. reflectance, temperature, height etc.
•EM radiation is what we measure in RS
•Blackbody concept used to explain energydistribution of sun / Earth
–Stefan-Boltzmann law explains total energy
–Wien’s law explains shift of max with decreasing T
–Planck’s Law explains shape of BB energy distribution
–BUT remember, no object is really a blackbody – only anapproximation
Dr. Hassan J. Eghbali
MODIS: building global picture
Dr. Hassan J. Eghbali
IKONOS & QuickBird: very local view!
•QuickBird: 16.5km swath at nadir, 61cm!panchromatic, 2.44m multispectral
•http://www.digitalglobe.com
•IKONOS: 11km swath at nadir, 1mpanchromatic, 4m multispectral
•http://www.spaceimaging.com/
Dr. Hassan J. Eghbali
Ikonos: high res. commercial
http://www.spaceimaging.com/gallery/spacepics/khaolak_side_by_side.jpg
Dr. Hassan J. Eghbali
Ikonos: highres.commercial
http://www.euspaceimaging.com/sime.asp?page=Gallery
Dr. Hassan J. Eghbali