Transcript Radiometric Theory and Vegetative Indices

Radiometric Theory
and
Vegetative Indices
Sensor-Based
Nitrogen Management
Decision Making
And Agronomic Strategy
Variable Rate
Nozzle System
Computer and
Sensor
Assembly
Direction
of Travel
Plant
Why Optical Sensing in
Precision Farming?
• Used to quantitatively describe 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 in conducting remote
sensing
– Variability in light source
– Filtering of light along path
– Measuring units/calibration
of sensing system
– Geometry
– Spatial and temporal
frequency of measurements
Light
Source
Sensing
System
Reflected Light
Plant or Soil
Surface
Fiber-Optic Spectrometer
One Spectral Channel at a time
Optical Grating
Analog to
Digital
Converter
CPU
Element
selection
Computer
Photo Diode Array
Optical
Glass
Fiber
Fundamentals 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)
Photo-Chemistry

Light may be absorbed and participate (drive) a
chemical reaction. Example: Photosynthesis in
plants
6CO2  6 H2 O  h  C6 H12 O6  6O2

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 structure
Silicon Responsivity
Primary and secondary
absorbers in plants
• Primary
– Chlorophyll-a
– Chlorophyll-b
• Secondary
– Carotenoids
– Phycobilins
– Anthocyanins
Plant Reflectance
Reflectance (%)
0.5
0.25
Visible
Near Infrared
Indicator of
Available
Chlorophyl
Measure of living
plant cell’s ability
to reflect infrared
light
Photosynthetic
Potential
0.00
450 500 550 600 650 700
750 800
850 900
Wavelength (nm)
950 1000 1050
Spectral Response to Nitrogen
1
0.9
Winter Wheat at Feekes 5 in potted soil
0.8
Reflectance
0.7
0.6
0.5
0 Nitrogen
0.4
100 lb Nitrogen/ac
0.3
Measure of
living plant
cell’s ability to
reflect infrared
light
Photosynthetic
Potential
0.2
0.1
0
400
500
450
600
550
Wavelength, nm650
700
800
Soil and crop reflectance
0.6
17 Corn
73 Cotton
9 Sunflower
Fractional Reflectance
0.5
27 Soybeans
0.4
25 Potatoes
0.3
43 Soils
0.2
P. S. Thenkabail
R. B. Smith
E. De Pauw
Yale Center for Earth Observation
0.1
0
300
400
500
600
700
800
Wavelength (nm)
900
1000
1100
Reflectance Indices
Based on ratios of Red and NIR Reflectance
Red Reflectance:
Rred
Rnir
rred = Rred / Ired
NIR Reflectance:
rnir = Rred / Ired
Ired
Inir
Vegetative
Index:
rRe d
Simple Ratio 
r NIR
Reflectance is primarily
a function of target
NDVI
• Normalized Difference Vegetative Index
r NIR  r RED
NDVI 
r NIR  r RED
• Developed as an irradiance index for remote
sensing
• Varies from -1 to 1
• Soil NDVI = -0.05 to .05
• Plant NDVI = 0.4 to 0.9
• Typical plants with
soil background NDVI=0.3-0.8
• NDVI from different sources vary
– Bandwidths for Red, NIR vary
– Irradiance vs. reflectance based
Normalized Difference Vegetative
Index - NDVI
• Calculated from the red
and near-infrared bands
• Equivalent to a plant
physical examination
• Correlated with:
– Plant biomass
– Crop yield
– Plant nitrogen
– Plant chlorophyll
– Water stress
– Plant diseases
– Insect damage
GreenSeekerTM Sensor
Light Detection and
Filtering
Detection of
Reflected
NIR and RED
+Sun
Direction
NIR and RED
Modulated
Illumination
Target
Sensor
Function
Light signal
Light
detection
Light
generation
?Calculate NDVI
?Lookup valve setting Valve settings
?Apply valve setting
?Send data to UI
“Sensor”
Valves
and
Nozzles