Illumination Radiation & The Atmosphere (x 2) Interaction with the Target Detection

1. What is Remote Sensing • Illumination • Radiation & The Atmosphere (x 2) • Interaction with the Target • Detection • Transmission & Storage • Image Processing • GIS Application

2. Illumination

3. EM Spectrum in Daily Life

4. Quantum Theory • Photons: quantum unit of electromagnetic (EM) radiation. Bundles of light or EM force. Discrete packets of energy (E = hn). • Photons travel at c (3 x 108 m/s). They are massless, but have finite momentum (p = E/c). • Photons are emitted by thermally-excited matter and during nuclear reactions. They can be reflected, refracted, absorbed, and scattered. They can also be diffracted and made to self-interfere!…

5. Particles and Waves Young’s Double Slit Experiment

6. Electromagnetic Waves • Oscillating E and B fields orthogonal to one another. • Fields are in phase with same amplitude and wavelengths. • EM waves can propagate through a vacuum at speed of light.

7. Electromagnetic Waves

8. Energy vs. Wavelength E = h n c = l n E = hc/l • Energy in a photon (electromagnetic wave) is inversely proportional to the wavelength (l)… • At longer l, there is less and less energy to sense • Long integration times or large sampling areas needed at long l • Lower resolution product at long l

9. TheElectromagnetic Spectrum

10. TheElectromagnetic Spectrum

11. TheElectromagnetic Spectrum Some minerals flouresce in the visible when illuminated by UV radiation

12. TheElectromagnetic Spectrum • Violet: 0.4 - 0.446 microns • Blue: 0.446 - 0.5 microns • Green: 0.5 - 0.578 microns • Yellow: 0.578 - 0.592 microns • Orange: 0.592 - 0.620 microns • Red: 0.620 - 0.7 microns

13. Color “subtractive color”

14. Color cyan red magenta green blue yellow Subtractive Color Matching (CYMK) Additive Color Matching (RGB) Light Beams Adding (monitors, emission) Dye Patches Subtracting (printers, absorption)

15. TheElectromagnetic Spectrum • IR is 100 times wider than visible (0.7 - 100 microns) • Near: 0.7 - 2 or 3 microns • Mid (Shortwave): 2 or 3 - 5 or 8 microns • Far (Thermal): 5 or 8 - 14 + microns • Only the TIR is “heat” emission • VNIR and SWIR are reflective

16. TheElectromagnetic Spectrum • 1 mm to 1 m wavelengths • Includes sub-millimeter, millimeter (T-rays), and RADAR • Bridges thermal and radio radiation

17. Sources of EM Radiation • Depends on the energy e.g. wavelength (l) • Nuclear reactions, atomic dissociations (ionization) generate gamma and X rays (high energy, small l) • Electronic excitations/transitions generate UV to visible photons (less energy, long l) • Molecular bond vibrations, molecular rotations generate IR photons (even less energy, long l) • Incident photons of a given energy can cause molecular, electronic, or atomic interactions in target…

18. Generation of EM Radiation • EMR generated when an electric charge is accelerated e.g. size or direction of the E and/or B field is variated with time at its source • Transformation of energy from other forms: • Kinetic • Chemical • Thermal • Electrical • Magnetic • Nuclear • Wavelength dependent • The more “organized” (e.g. not random) the mechanism is, the more “coherent” (e.g. narrower in spectral bandwidth) the EM radiation produced

19. Generation of EM Radiation • Radio generated by… • periodic currents of electric charges in wires, electron beams, antennas • Dipole antenna: connect, two, straight wires to opposing terminals of an AC source -> electric charges will be moved back and forth --> variable E and B fields generated --> EM wave with frequency of current • Microwaves generated by… • Electron tubes where electrons move at high speed --> produce EM wave • Molecular excitation in a maser --> device excites different levels of rotational energy in molecule --> relaxation to ground states emits excess energy as EM wave • Visible and IR… • Molecular excitation (vibrational,and rotational) followed by decay • At shorter wavelengths due to quantized energy levels of electronic orbitals • Excitation achieved with electric discharges, chemical reactions, illumination with photons • Blackbody radiation (TIR)… • Higher energies… • Gamma rays, X-rays, etc. produced by nuclear decay processes

20. Physical Phenomena and EM Radiation

21. Physical Phenomena and EM Radiation

22. Blackbody Radiation Blackbody: Hypothetical perfect radiator, absorber, and emitter. Absorbs and re-radiates all incident energy when it has T above 0 K. Stefan-Boltzmann Law Etot=s T4 lmax=3 x 107 / T Wien’s Law E(l,T)=(2hc2/l5){1/[exp(hc/lkT)– 1]}

23. Solar Irradiance • The Sun has a blackbody temperature of ca. 5800 K and a peak in its Stefan-Boltzmann curve at 0.48 mm (visible green). Why is the sun yellow, though? • Earth’s blackbody temperature is ca. 300 K --> 9.7 mm peak (TIR).

25. Interaction of EM Waves with Matter • Atomic and molecular systems exist in certain stationary states with well-defined energy levels. • For isolated atoms, levels are related to orbitals and spins of electrons. • For molecules, levels are related to rotational and vibrational states • The distribution of energy levels depends on the atomic/molecular structure of the material. • For crystalline solids, their crystalline nature will be important • For metals and semi-conductors, electron bands will be important

26. Statistical Mechanics Boltzmann’s Law • Thermal equilibrium • Population of certain level given by Boltzmann’s Law • At T = 0, all population at ground state • Higher energy levels less populated than lower ones

27. Absorption, Exitation, and Emission

28. Wave-Matter Interactions

29. Interaction of EM Waves with Matter • Gamma & X-rays (> 40 eV) • Photoelectric effect: absorption of photon, ejection of electron • Compton effect: absorption of photon, ejection of electon & emission of lower energy photon • Pair production: absorption of photon, generation of electron-positron pair • Radioactivity • UV (3-40 eV) • Electronic exitation and transfer • Atmospheres

30. Interaction of EM Waves with Matter • VNIR (0.2-3 eV) • Electronic exitations and transitions • In solids, molecular vibrations, ionic vibrations, crystal field effects, charge transfer, conduction bands, band gaps (e.g. semi-conductors) • Fe3+: 0.84-0.92 micron absorption (Fe oxides and hydroxides) • Chlorophyll: 0.75 micron feature (red edge) • OH: fundamental and overtone features at 2.1-2.8 microns (clays) • SWIR & TIR (8 to 14 microns) • Si-O stretching vibration (silicate rocks) • Restrahlen bands: bands of metallic-like reflection (interconnection of Si-O tetrahedra) • Vibrational exitations (e.g. atmosphere) • Thermal emission dependent on temperature and radiation governed by Planck’s Law (blackbody)

31. Interaction of EM Waves with Matter • Submillimeter • Rotational excitation (water, oxygen, etc.) • Atmospheres • Microwave ( < 20 GHz, > 1.5 cm) • Little band information concerning composition • Interactions result from electronic conduction, nonresonant magnetic and electric effects, structure • Example: • When wave interacts with a molecule, displacement of electrons forms an oscillating dipole --> induced EM field • Induced EM field moves through material at < c as dictated by index of refraction/dielectric constant • Anisotropy or loss of energy will depend on compostion and structure of medium (e.g. interfaces, roughness) • Visible-Infrared: chemical properties • TIR: thermal properties • Microwave: physical and electrical properties

32. Wave-Matter Interactions

33. Hydrogen

34. Spectral Emission Lines

35. Spectral Absorption Lines

36. Spectra

38. Interaction of EM Waves with Matter • Microscopic view e.g. molecular and atomic interactions • Mechanisms are largely energy (e.g. frequency or wavelength) dependent • If a photon of a given energy interacts with matter, there will be an exchange of energy • electrons, molecules, nuclei will be put into motion • e.g. decay, excitation, rotation, vibration, displacement

40. Interactions with the Atmosphere Scattering Absorption

41. Scattering • Mie scattering: dispersion of radiation by particles of size o(l), usually vapor & dust. • Rayleigh scattering: scattering due to constituents of size < l. Increases with shorter l and larger optical depth. Reason for the blue sky. Reason for red sunsets and sunrises. Dominant mechanism. • Nonselective scattering: wavelength-independent scattering due to particles > l. Reason why clouds are white. • Backscatter is major secondary source of photons to a sensor (80-90% of f)! Critical source of “non-data” in optical imagery.

42. Scattering Rayleigh scattering ~1/4

43. Rayleigh Scattering Path length is important

44. Non-Selective Scattering

45. Absorption • Aerosols and molecular constituents produce substantial scattering at all wavelengths. Also… • Gases in the atmosphere preferentially absorb or transmit incident photons (e.g. solar radiation) of certain wavelengths. H2O, CO2, O3, and O2are most important culprits. • These gases can also become exited and emit photons (secondary source), sometimes at certain wavelengths different than those they absorb.

46. Atmospheric Interactions Amount of atmospheric absorption also depends on altitude…

47. Seniors are tuned to various bands Sensor bands must avoid atmospheric absorptions

48. Interaction Between EM Energy & Surfaces • Diffraction • Scattering • Reflection • Refraction • Transmission • Absorption, excitation, & emission • Dispersion

49. Interaction with the Target

50. Reflectance and Roughness • Two types of reflecting surfaces: • Smooth: reflects all incident energy according to Snell’s Law (angle of incidence, etc.). Specular reflector. • Rough: diffuse scattering of incident energy in some hemispherical distribution. Bragg scatterer.