Optical sensing in Precision Farming (Techniques) Aerial remote sensing Film (visible/NIR/IR) and...
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Optical sensing in Precision Farming Optical sensing in Precision Farming (Techniques)(Techniques)Optical sensing in Precision Farming Optical sensing in Precision Farming (Techniques)(Techniques)
Aerial remote sensing• Film (visible/NIR/IR) and digitization• Direct Digital recording
Field machine based remote sensing• Direct Digital recording
Manual crop survey methods• Direct Digital (manual recording /logging)
Aerial remote sensing• Film (visible/NIR/IR) and digitization• Direct Digital recording
Field machine based remote sensing• Direct Digital recording
Manual crop survey methods• Direct Digital (manual recording /logging)
Purpose for use of optical sensing in Purpose for use of optical sensing in Precision FarmingPrecision FarmingPurpose for use of optical sensing in Purpose for use of optical sensing in Precision FarmingPrecision Farming
Used to characterize plant or soil status• Requirement: Calibration of spectral parameters to
status
Used to characterize boundaries– Physical– Morphological
• Requirement: Accurate spatial calibration(1m actual = 1 pixel)Lat/Lon = f(pixel
position)
Used to characterize plant or soil status• Requirement: Calibration of spectral parameters to
status
Used to characterize boundaries– Physical– Morphological
• Requirement: Accurate spatial calibration(1m actual = 1 pixel)Lat/Lon = f(pixel
position)
Issues - What is being measured?Issues - What is being measured?Issues - What is being measured?Issues - What is being measured?
– Variability in light source– Filtering of light along path– Measuring units/calibration
of sensing system– Geometry– Spatial and temporal
frequency of measurements
LightSource
Plant or SoilSurface
Reflected Light
SensingSystem
Typical Multi-Spectral Sensor Typical Multi-Spectral Sensor ConstructionConstructionTypical Multi-Spectral Sensor Typical Multi-Spectral Sensor ConstructionConstruction
Analog toDigitalConverter
Computer
One Spectral Channel
Photo-DiodeAmplifier
Filter
Collimator
Target
Illumination
CPU
Radiometer
Fiber-Optic SpectrometerFiber-Optic SpectrometerFiber-Optic SpectrometerFiber-Optic Spectrometer
OpticalGlass Fiber
Photo Diode Array
Optical GratingAnalog toDigitalConverter
Computer
CPU
Fundamentals of LightFundamentals of LightFundamentals of LightFundamentals of 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)
Relationship between frequency and Relationship between frequency and wavelengthwavelengthRelationship between frequency and Relationship between frequency and wavelengthwavelength
Plus
Minus Minus
Plus
Relationship between frequency and Relationship between frequency and wavelengthwavelength
c
Wavelength = speed of light divided by frequency
(miles between bumps = miles per hour / bumps per hour)
Relationship between frequency and Relationship between frequency and wavelengthwavelengthRelationship between frequency and Relationship between frequency and wavelengthwavelength
Plus
Minus Minus
Plus
Antenna
+ - 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 m
Light emission / absorption governed Light emission / absorption governed by quantum effectsby quantum effects
Planck - 1900Planck - 1900
E nh E is light energy fluxn is an integer (quantum)h is Planck’s constant is frequency
E hp Einstein - 1905Einstein - 1905
One “photon”
Changes in energy states of matter are Changes in energy states of matter are quantitizedquantitized
Bohr - 1913Bohr - 1913
h E Ek j
Where Ek, Ej are energy states (electron shell states etc.) and frequency, , is proportional to a change of state
and hence color of light. Bohr explained the emission spectrum of hydrogen.
Where Ek, Ej are energy states (electron shell states etc.) and frequency, , is proportional to a change of state
and hence color of light. Bohr explained the emission spectrum of hydrogen.
Hydrogen Emission Spectra (partial representation)
Wavelength
Photo-ChemistryPhoto-ChemistryPhoto-ChemistryPhoto-Chemistry
Light may be absorbed and participate (drive) a chemical reaction. Example: Photosynthesis in plants
Light may be absorbed and participate (drive) a chemical reaction. Example: Photosynthesis in plants
6 6 62 2 6 12 6 2CO H O h C H O O
The frequency (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 structure
The frequency (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 structure
Visual reception of colorVisual reception of colorVisual reception of colorVisual 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)
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)
Wavelength
Primary and secondary absorbers in Primary and secondary absorbers in plantsplantsPrimary and secondary absorbers in Primary and secondary absorbers in plantsplants
Primary– Chlorophyll-a– Chlorophyll-b
Secondary– Carotenoids– Phycobilins– Anthocyanins
Primary– Chlorophyll-a– Chlorophyll-b
Secondary– Carotenoids– Phycobilins– Anthocyanins
SunlightSunlight
Chlorophyll bChlorophyll b
B-CaroteneB-Carotene
PhycocyaninPhycocyanin
Chlorophyll aChlorophyll a
300 400 500 600 700 800 300 400 500 600 700 800
Wavelength, nmWavelength, nm
Ab
sorp
tio
nA
bso
rpti
on
Lehninger, Nelson and CoxLehninger, Nelson and Cox
Absorption of Visible Lightby Photopigments
Absorption of Visible Lightby Photopigments
0.25
0.5
Wavelength (nm)
Ref
lect
ance
(%
)R
efle
ctan
ce
(%)
VisibleVisible Near InfraredNear Infrared
450 550 650 750 850 950 1050 1150500 600 700 1000900800 1100
0.00
Plant Reflectance
Soil and crop reflectanceSoil and crop reflectanceSoil and crop reflectanceSoil and crop reflectance
0
0.1
0.2
0.3
0.4
0.5
0.6
300 400 500 600 700 800 900 1000 1100
Wavelength (nm)
Fra
cti
on
al
Re
fle
cta
nc
e
43 Soils
27 Soybeans
25 Potatoes
9 Sunflower
73 Cotton17 Corn
P. S. ThenkabailR. B. SmithE. De PauwYale Center for Earth Observation
Soil Reflectances - OklahomaSoil Reflectances - OklahomaSoil Reflectances - OklahomaSoil Reflectances - Oklahoma
0
0.2
0.4
0.6
0.8
1
350 400 450 500 550 600 650 700 750 800
Wavelength (nm)
Ref
lect
ance
(Fra
ctio
n)
Tipton Stillwater
Perkins Mangum
Lahoma Haskell
Goodwell Ft. Cobb
Chickasha Altus
Agron. Stwr.
Thermal Nature of the Emission of Thermal Nature of the Emission of RadiationRadiationThermal Nature of the Emission of Thermal Nature of the Emission of RadiationRadiation
Black-body radiation– Matter is made up of inter-related particles
which may be considered to vibrate or change energy state
– A distribution of energy states exists within a blackbody
– Matter emits radiation in proportion to the energy state changes
Black-body radiation– Matter is made up of inter-related particles
which may be considered to vibrate or change energy state
– A distribution of energy states exists within a blackbody
– Matter emits radiation in proportion to the energy state changes
Wien’s Displacement LawWien’s Displacement LawWien’s Displacement LawWien’s Displacement Law
peak = 2,897,000 / Twhere: T = [ 0K ] = [ nm]Hot metal examplepeak-sun = 2,897,000/6000 = 475nmpeak-plant = 2,897,000/300 = 9700nm
Point: Emission “color = f(T of emitter)
peak = 2,897,000 / Twhere: T = [ 0K ] = [ nm]Hot metal examplepeak-sun = 2,897,000/6000 = 475nmpeak-plant = 2,897,000/300 = 9700nm
Point: Emission “color = f(T of emitter)
Planck’s LawPlanck’s Law
Rc h
ef Thc
k T
2 1
1
2
5 ( , )
Equation:
Point: Emission “color = f(T of emitter)
Sun vs. Plant / Soil radiationSun vs. Plant / Soil radiation
0
25
50
75
100
0 2500 5000 7500 10000 12500 15000
Wavelength (nm)
Rad
ian
ce (
%)
Radiance of 6000 K Object
Radiance of 300 K Object
6000K
300K
SUN
Terrestrial
Radiation Energy BalanceRadiation Energy BalanceRadiation Energy BalanceRadiation Energy Balance
Earth
SUN
Temperature of the earth is set bythe difference betweenabsorbed and emitted energy
If no energy was emitted by the earth,The earth’s temperature would eventually rise to that of the sun
Temperature of the earth is set bythe difference betweenabsorbed and emitted energy
If no energy was emitted by the earth,The earth’s temperature would eventually rise to that of the sun
Nature of absorption by the atmosphereNature of absorption by the atmosphereNature of absorption by the atmosphereNature of absorption by the atmosphere
IncidentIncidentReflectedReflected
TransmittedTransmitted
AbsorbedAbsorbedRadiant energy balance mustbe computed for eachcomponent of the atmosphereand for each wavelengthto estimate the radiationincident on the earth's surface
Radiant energy balance mustbe computed for eachcomponent of the atmosphereand for each wavelengthto estimate the radiationincident on the earth's surface
Earth'ssurface
Atmosphere
550 650450
0
100
200
300
400
500
600
700
0 250 500 750 1000 1250 1500 1750 2000Wavelength (nm)
Sp
ectr
al
Irra
die
nce (
w/m
^2 n
m)
Extraterrestrial SolarIrradience
Terrestial SolarIrradience
Adapted from Thekaekara, M. P. 1973.Solar Energy Outside the Earth's Atmosphere.Solar Energy, Vol 14, p 109.
Solar IrradianceSolar Irradiance
NIRUV
Radiation Energy BalanceRadiation Energy BalanceRadiation Energy BalanceRadiation Energy Balance
Incoming radiation interacts with an object and may follow three exit paths:
• Reflection• Absorption• Transmission
+ + rf = 1.0, , and rf are the
fractions taking each path
Incoming radiation interacts with an object and may follow three exit paths:
• Reflection• Absorption• Transmission
+ + rf = 1.0, , and rf are the
fractions taking each path
R0
R0
R0 rf
R0
ReflectanceReflectanceReflectanceReflectance
Ratio of incoming to reflected irradiance Incoming can be measured using a
“white” reflectance target Reflectance is not a function of incoming
irradiance level or spectral content, but of target characteristics
Ratio of incoming to reflected irradiance Incoming can be measured using a
“white” reflectance target Reflectance is not a function of incoming
irradiance level or spectral content, but of target characteristics
Diffuse and Specular RadiationDiffuse and Specular Radiation
Multiple reflections in the atmospherecause diffuse radiationMultiple reflections in the atmospherecause diffuse radiation
SpecularTarget
Source
Measurement of LightMeasurement of LightMeasurement of LightMeasurement of Light
Photometry• Measurement of visible radiation in terms of
sensitivity of the human eye.• Used in photography and in lighting performance• Photometric measures
– Luminous intensity - Candela [cd]
– Luminous Flux - Lumen [lm]
– Luminance (cd/m2) - [nit]
– Illuminance (lm/m2) - [lx]
Photometry• Measurement of visible radiation in terms of
sensitivity of the human eye.• Used in photography and in lighting performance• Photometric measures
– Luminous intensity - Candela [cd]
– Luminous Flux - Lumen [lm]
– Luminance (cd/m2) - [nit]
– Illuminance (lm/m2) - [lx]
Measurement of LightMeasurement of LightMeasurement of LightMeasurement of Light
Radiometry– Measurement of the properties of light without
regard to human perception– Used for quantifying energy in radiation– Radiometric Measures
• Radiant Flux - Watt (W) (rate of energy from source)
Radiometry– Measurement of the properties of light without
regard to human perception– Used for quantifying energy in radiation– Radiometric Measures
• Radiant Flux - Watt (W) (rate of energy from source)
TerminologyTerminologyTerminologyTerminology
Radiant flux– Energy in the form of radiation from a source
per unit time units passing through a surface = Watt [W]
– irradiance• irradiate - to have light radiating on to an object• irradiance - the light emitted from an object surface
that is being irradiated
Radiant flux– Energy in the form of radiation from a source
per unit time units passing through a surface = Watt [W]
– irradiance• irradiate - to have light radiating on to an object• irradiance - the light emitted from an object surface
that is being irradiated
RadianceRadianceRadianceRadiance
Energy Flux through a surface per unit of solid angleper unit area of sourceEnergy Flux through a surface per unit of solid angleper unit area of source
Solid AngleSteridian [St]Solid AngleSteridian [St]
WattsWatts
per meter square of sourceper meter square of source
Stm
WR
2
IrradianceIrradiance
Energy Flux through a surface per unit of areaEnergy Flux through a surface per unit of area
Unit Area (m2)
Power = Energy / Time [Joules / Second] = [Watts]Power = E / TimePower = Photons / TimePower = nh/TimeIrradiance = Power / Area = (Photons / Time) / AreaIrradiance = [Watts / Square Meter]
2m
WI
Irradiance and ReflectanceIrradiance and ReflectanceIrradiance and ReflectanceIrradiance and Reflectance
Irradiance (I0) a measure of power per unit area
Reflectance (rf ) is the ratio of reflected to incident Irradiance rf = I0 rf / I0
Irradiance (I0) a measure of power per unit area
Reflectance (rf ) is the ratio of reflected to incident Irradiance rf = I0 rf / I0
0
100
200
300
400
500
600
700
0 250 500 750 1000 1250 1500 1750 2000
Wavelength (nm)
Sp
ec
tra
l Irr
ad
ian
ce
(w
/m^
2 n
m)
Area = [ W/m2 ] = Irradianceheight = [ W/m2 nm ] = Spectral Irradiancewidth = [ nm ] = Bandwidth
Sp
ectr
al
Irra
dia
nce
Bandwidth
Spectral IrradianceSpectral IrradianceSpectral IrradianceSpectral Irradiance
– Power per unit spectral width– Power per unit spectral width
max
min
dII
Computation of Irradiance from Spectral Computation of Irradiance from Spectral IrradianceIrradianceComputation of Irradiance from Spectral Computation of Irradiance from Spectral IrradianceIrradiance
Irradiance for a particular band is the “sum” of Spectral Irradiance across the band times the wavelength
Irradiance for a particular band is the “sum” of Spectral Irradiance across the band times the wavelength
RedNIR
RedNIR
II
IINDVI
NDVINDVINDVINDVI
– Normalized Difference Vegetative Index• Difference increases with greater red absorption• Increase or decrease in total irradiance does not
effect NDVI• Typically computed with irradiances, use of
reflectance eliminates spectral shift sensitivity
– Normalized Difference Vegetative Index• Difference increases with greater red absorption• Increase or decrease in total irradiance does not
effect NDVI• Typically computed with irradiances, use of
reflectance eliminates spectral shift sensitivity
OSU Irradiance ratio sensorOSU Irradiance ratio sensorOSU Irradiance ratio sensorOSU Irradiance ratio sensor
Plant and Soil target
Micro-Processor, A/D Conversion, and Signal Processing
Ultra-SonicSensor
Photo-Detector
Optical Filters
Collimation
Inir
Rnir
Ired
Rred
Irradiance IndicesIrradiance IndicesIrradiance IndicesIrradiance Indices
Spectral shift in illuminationprevents use ofsimple irradiance sensing
Based on ratios of reflectedRed and NIR intensity
Example Index:Rred / Rnir
Inir
Rnir
Ired
R red
Reflectance IndicesReflectance IndicesReflectance IndicesReflectance Indices
Based on ratios ofRed and NIR Reflectance
Red Reflectance: = Rred / Ired
Example Index:red / nir
Reflectance is primarilya function of target
NDVINDVINDVINDVI
dNIR
dNIRNDVIRe
Re
Developed as an irradiance Index for application to remote sensing
Normalized Difference Vegetative Index Varies from -1 to 1
• Soil NDVI = -0.05 to .05• Plant NDVI = 0.6 to 0.9• Typical plants with
soil background NDVI=0.3-0.8
OSU sensors– narrow-band
reflectance based NDVI
Developed as an irradiance Index for application to remote sensing
Normalized Difference Vegetative Index Varies from -1 to 1
• Soil NDVI = -0.05 to .05• Plant NDVI = 0.6 to 0.9• Typical plants with
soil background NDVI=0.3-0.8
OSU sensors– narrow-band
reflectance based NDVI
Photo-Detector
Turf target
Optical Filters
Fiber OpticLight Guides
GlassCover
Collimation
Sensor/AmplifierIntegrated Circuit
OSU Reflectance SensorOSU Reflectance SensorOSU Reflectance SensorOSU Reflectance Sensor
OSU Reflectance SensorOSU Reflectance SensorOSU Reflectance SensorOSU Reflectance Sensor
Natural Illumination
Battery powered
Wide dynamic range
Low noise
0.75 x 0.25 m field of view
Natural Illumination
Battery powered
Wide dynamic range
Low noise
0.75 x 0.25 m field of view
NDVINDVINDVINDVI
0
50
100
150
200
250
300
350
400
450
0 500 1000 1500 2000 2500
Wavelength (nm)
Te
rre
sti
al S
ola
r Ir
rad
ien
ce
(W
/M^
2-n
m)
0
10
20
30
40
50
60
70
80
90
100
Co
mp
ute
d P
lan
t A
bs
orb
an
ce
Sp
ec
tra
(%
)
Terrestial Solar Irradience
Computed PlantReflectance Spectra
Plant with lowerphotosynthetic activity
IRED =671 nm
INIR = 780 nm
Photo Diode DetectorPhoto Diode Detector
Photo Diode Area2.29mm x 2.29mm
5.2e-6 m2
Opto 202Die Topography
Silicon ResponsivitySilicon Responsivity
Calculation of Irradiance from Detector Calculation of Irradiance from Detector outputoutputCalculation of Irradiance from Detector Calculation of Irradiance from Detector outputoutput
Responsivity: [V/uW]for a particular wavelength, output in volts, V is the product ofResponsivity times the Irradience I times sensor area.
V I A106 [ W/m2 ] [V/uW] [m2]
For a wide band,
V I Ad 106
min
max
Calculation of Irradiance from Sensor Calculation of Irradiance from Sensor output -cont-output -cont-Calculation of Irradiance from Sensor Calculation of Irradiance from Sensor output -cont-output -cont-
Irradiance may be computed from thevoltage reading for a narrow spectral band :
KVA
VI
610
The average value of Responsivity, for the detector must be used
Calculation of Irradiance from Sensor Calculation of Irradiance from Sensor output -cont-output -cont-Calculation of Irradiance from Sensor Calculation of Irradiance from Sensor output -cont-output -cont-
Sensor reading, S, is normally an amplified anddigitized numeric value
SV
VRange
n 2 Where: V voltage output of the sensor VRange input range of the amplifier-A/D circuit n binary word width of the A/D converter
SI A
VRange
n10
26
Calculation of Irradiance from Sensor Calculation of Irradiance from Sensor output -contoutput -contCalculation of Irradiance from Sensor Calculation of Irradiance from Sensor output -contoutput -cont
Example:Let I = 1 W/m2
A = 5.2e-6 m2 (for the Burr-Brown 201)
= 0.5 V/W (for = red)VRange = 5 Vn = 12 bits
SI A
VRange
n
10
210 1 05 52 10
52 2130
6 6 612 . .
S kI