Color and Spectral Signatures Steve Dutch University of Wisconsin-Green Bay

It’s a Colorful World

Color and Wavelength

Color Formalisms Physical Optics – Scattering is most important in Remote Sensing Color Centers and Crystal-Field Effects – Individual atoms interact with light Inter-Atomic Interactions – Charge transfer – Molecular orbitals – Vibrations Band Theory – Applicable to radar, not much to passive remote sensing

Physical Optics Scattering – Particulate Matter Dispersion – Rainbows, etc. Interference – Oil slicks, sea shells Diffraction – Opal, CD’s

Scattering

Anti-Crepuscular Rays

Major Types of Scattering Rayleigh scattering – Small particle compared to wavelength of light Mie scattering – Particle about the same size as wavelength of light Geometric scattering – Particle much larger than wavelength of light

Rayleigh Scattering Molecules and nanoparticles Proportional to 1/λ 4 Blue vs. Red = (700nm/400nm) 4 = 9.4 Why the sky is blue Why isn’t the sky purple? – Less sunlight – Lower eye sensitivity – Greater absorption UV Scattering useful in particle studies

Mie Scattering Responsible for most white colors Cloud particles Oil droplets in contaminated water Suspended sediment Algal blooms

Multiple and Mie Scattering

Backscattering

Atomic Emission and Absorption

Quantum Pinball

Fluorescence (Sunlight and laser induced fluoresence in chlorophyll)

Phosphorescence

Electrons and Light

Coloring Agents in Minerals

Iron is the Main Source of Color in Rocks and Soils

Charge Transfer

Electron bumped between atoms Extremely effective absorption mechanism A major reason UV is not very useful for surface remote sensing Very strong UV and blue absorption in iron oxide Why we have “earth tones”

Molecular Orbitals

Chlorophyll

Water Vibration Modes

What Color is Water?

What Color is Ice?

Spectrum of Water