SpectroscopyElectrical and magnetic propertiesFundamentals of high frequency electromagnetic waves (Light)The electromagnetic spectrumRelationship between frequency and wavelengthSlide 6Plants light harvesting structure - modelLight emission / absorption governed by quantum effectsFrequency bands and photon energyChanges in energy states of matter are quantifiedMeasurement of reflected intensity – Typical Multi-Spectral Sensor ConstructionMeasurement of reflected intensity - Fiber-Optic SpectrometerVisual reception of colorQuantification of colorCIE XYZ modelCIE Lab modelPhoto-ChemistrySilicon ResponsivityPrimary and secondary absorbers in plantsChlorophyll absorbanceRadiation Energy BalanceInternal Absorbance (Ai)ReflectanceSolar IrradianceSoil and crop reflectanceSoil Reflectances - OklahomaElectromagnetic propertiesSlide 28Slide 29Slide 30Slide 31Slide 32Slide 33Electromagnetic properties Resistance, Capacitance and Dielectric PropertiesElectromagnetic properties Resistance, Capacitance and Dielectric PropertiesSlide 36Slide 37Slide 38Slide 39Slide 40Slide 41Electromagnetic properties101/14/19 BAE2023 Physical Properties of Biological Materials1Spectroscopy201/14/19 2Electrical and magnetic properties•Electromagnetic fields are propagated through and reflected by materials–Characterized as:•Current flow at low frequencies•Magnetism in metals•Optical absorbance / reflectance in light•Frequency is a major factor in the primary characteristics–Low frequency – “electrical” properties–High frequency – “optical” properties301/14/19 3Fundamentals of high frequency electromagnetic waves (Light)•Light = Energy (radiant energy)–Readily converted to heat•Light shining on a surface heats the surface•Heat = energy•Light = Electro-magnetic phenomena–Has the characteristics of electromagnetic waves (eg. radio waves)–Also behaves like particles (e.g.. photons)401/14/19 4The electromagnetic spectrum501/14/19 5Relationship between frequency and wavelengthPlusMinus MinusPlusWavelength = speed of light divided by frequency(miles between bumps = miles per hour / bumps per hour)= Wavelength [m]= Frequency [Hz]c = 3x108 m/s in a vacuumc601/14/19 6Relationship between frequency and wavelengthPlusMinus MinusPlusAntenna+ - KOSU = 3 x 108 / 97.1 x 106 KOSU = 3 m red = 6.40 x 10- 7 m = 640 nmBohr’s Hydrogen = 5 x 10 - 11 m701/14/19 7Plants light harvesting structure - modelJungas et. al. 1999801/14/19 8Light emission / absorption governed by quantum effectsPlanck - 1900E nhE is light energy fluxn is an integer (quantum)h is Planck’s constant is frequency E hpEinstein - 1905One “photon”901/14/19 9Frequency bands and photon energy1001/14/19 10Changes in energy states of matter are quantifiedBohr - 1913h E Ek j Where Ek, Ej are energy states (electron shell states etc.) and frequency, , is proportional to a change of stateand hence color of light. Bohr explained the emission spectrum of hydrogen. Hydrogen Emission Spectra (partial representation)Wavelength1101/14/19 11Measurement of reflected intensity –Typical Multi-Spectral Sensor ConstructionAnalog toDigitalConverterComputerOne Spectral ChannelPhoto-Diode detector/ AmplifierOptical FilterCollimatorTargetIlluminationCPURadiometer1201/14/19 12Measurement of reflected intensity - Fiber-Optic SpectrometerOpticalGlass FiberPhoto Diode ArrayOptical GratingAnalog toDigitalConverterComputerCPUElement selectionOne Spectral Channel at a time1301/14/19 13Visual reception of color•Receptors in our eyes are tuned to particular photon energies (hn)•Discrimination of color depends on a mix of different receptors•Visual sensitivity is typically from wavelengths of ~350nm (violet) to ~760nm (red)Wavelength400 nm700 nm500 nm1401/14/19 14Quantification of color•Spectral measurements can be used to quantify reflected light in energy and spectral content, but not very useful description of what we see.•Tri-stimulus models – represent color as perceived by humans–Tri-stimulus models•RGB - most digital work•CYM - print•HSI, HSB, or HSV - artists•CIE L*a*b*•YUV and YIQ - television broadcasts1501/14/19 15CIE XYZ model•Attempts to describe perceived color with a three coordinate system modelXYZ= luminance1601/14/19 16CIE Lab model•An improvement of the CIE XYZ color model.•Three dimensional model where color differences correspond to distances measured colorimetrically•Hue and saturation (a, b) –a axis extends from green (-a) to red (+a)–b axis from blue (-b) to yellow (+b)•Luminance (L) increases from the bottom to the top of the three-dimensional model•Colors are represented by numerical values•Hue can be changed without changing the image or its luminance.•Can be converted to or from RGB or other tri-stimulus models1701/14/19 17Photo-Chemistry•Light may be absorbed and precipitate (drive) a chemical reaction. Example: Photosynthesis in plants6 6 62 2 6 12 6 2CO H O h C H O O •The wavelength must be correct to be absorbed by some participant(s) in the reaction•Some structure must be present to allow the reaction to occur•Chlorophyll•Plant physical and chemical structure1801/14/19 18Silicon Responsivity1901/14/19 19Primary and secondary absorbers in plants•Primary–Chlorophyll-a–Chlorophyll-b•Secondary–Carotenoids–Phycobilins–Anthocyanins2001/14/19 20Chlorophyll absorbanceChla: blackChlb: redBChla: magentaBChlb: orangeBChlc: cyanBChld: bueBChle: greenSource: Frigaard et al. (1996), FEMS Microbiol. Ecol. 20: 69-772101/14/19 21Radiation Energy BalanceIncoming radiation interacts with an object and may follow three exit paths:• Reflection• Absorption• Transmission + + = 1.0, , and are thefractions taking each pathKnown as:fractional absorption coefficient,fractional transmittance, andreflectance respectivelyI0I0 I0Iout = I02201/14/19 22Internal Absorbance (Ai)•Lambert's Law - The amount of light absorbed is directly proportional to the logarithm of the length of the light path or the thickness of the absorbing medium. Thus: l = length of light pathk = extinction coefficient of medium•Normally in absorbance measurements the measurement is structured so that reflectance is
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