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Optical-Sensors. 0.50. Visible Light. Near Infrared. 0.25. % Reflectance. 450. 550. 650. 750. 850. 950. 1050. Wavelength nm. Example Index: R red / R nir. Spectral shift in illumination prevents use of simple irradiance sensing. Irradiance Sensing Strategies. - PowerPoint PPT Presentation
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Optical-SensorsOptical-Sensors
Wavelength nmWavelength nm
Visible LightVisible LightVisible LightVisible LightNear InfraredNear Infrared
450450 550550 650650 750750 850850 950950 10501050
0.250.25
0.500.50%
Ref
lect
ance
% R
efle
ctan
ce
Irradiance Sensing StrategiesIrradiance Sensing Strategies
Inir
Rnir
Ired
R red
Spectral shift in illuminationSpectral shift in illuminationprevents use ofprevents use ofsimple irradiance sensingsimple irradiance sensing
Example Index:Example Index:RRredred / / RRnirnir
Inir
Rnir
Ired
R redRed Red Reflectance:Reflectance:r = Rr = Rredred / I / Iredred
Reflectance is primarilyReflectance is primarilya function of targeta function of target
Reflectance Sensing StrategiesReflectance Sensing Strategies
nm670nm6780
nm670nm6780
dReNIR
dReNIRNDVI
Normalized Difference Normalized Difference Vegetative Index (NDVI)Vegetative Index (NDVI)
Incident
flectedRe
Inicident
flectedRe
Incident
flectedRe
Inicident
flectedRe
cetanflecRe
NIR
dRe
NIR
NIR
NIR
dRe
NIR
NIR
NDIV
Reflectance NDVIReflectance NDVI
Natural LightingNatural Lighting
• Light source is free.Light source is free.• Much of the effect of Much of the effect of
spectral shift can be spectral shift can be corrected by measuring corrected by measuring incident and reflected. incident and reflected. light and calculating light and calculating reflectance.reflectance.
• Spectral shifts occur as Spectral shifts occur as sun angle changes.sun angle changes.
• Cloud cover affects Cloud cover affects intensity.intensity.
• Moisture and dust cause Moisture and dust cause differences in refraction differences in refraction and absorbence across and absorbence across the spectra.the spectra.
• Can’t be operated at Can’t be operated at night. night.
AdvantagesAdvantages LimitationsLimitations
Photo-Detector
Target
Optical Filters
Fiber OpticLight Guides
GlassCover
Collimation
Sensor/AmplifierIntegrated Circuit
OSU Reflectance SensorOSU Reflectance Sensor
Artificial Lighting Artificial Lighting
• Patchen high frequency Patchen high frequency pulsed narrow spectra pulsed narrow spectra lightinglighting
• Broad spectra lighting with Broad spectra lighting with filters filters – ConstantConstant
or or – PulsedPulsed
Artificial LightingArtificial Lighting
• Removes the effect of Removes the effect of changing background changing background illumination.illumination.
• Can be operated 24 Can be operated 24 hours/day.hours/day.
• Can produce an Can produce an absolutely calibrated absolutely calibrated signal.signal.
• Choice of spectral bands Choice of spectral bands are limited when pulsed are limited when pulsed solid state lighting solid state lighting sources (LED’s or lasers) sources (LED’s or lasers) are used.are used.
• Broadband lighting Broadband lighting requires high power .requires high power .
• Cost of the Cost of the sensor/lighting systems sensor/lighting systems are higher than those are higher than those using natural lighting.using natural lighting.
Turf Target
NIR and REDModulated
Illumination
Direction
Patchen WeedseekerPatchen WeedseekerOptical SensorOptical Sensor
Patchen Sensing TechniquePatchen Sensing Technique
PhotodiodeDetector
Reflected Light
NIR+Red+Sun NIR+Red+Sun
Voltage Voltage
High PassFilter
NIR+Red
Patchen Sensing TechniquePatchen Sensing Technique
90o
RedNIR
NIR+Red
a
RNIR
RNIRa
a NDVI
Patchen Sensor NDVI CalibrationPatchen Sensor NDVI Calibration
y = 0.7711x - 1.0618
0.4
0.5
0.6
0.7
0.8
0.9
1
1.9 2.1 2.3 2.5 2.7
Patchen DET_OUT Voltage (x/6420)Patchen DET_OUT Voltage (x/6420)
OS
U N
DV
IO
SU
ND
VI
Good calibration to Good calibration to NDVI after filteringNDVI after filtering
11500
12500
13500
14500
40 60 80 100 120
Temperature (F)
DE
T_O
UT
* 6
420
Unit 3385
Unit 3386
Unit 3388
Unit 3493
Unit 3387
Temperature driftTemperature driftunacceptable for unacceptable for absolute measurementsabsolute measurements
Patchen Temperature Patchen Temperature CalibrationCalibration
y = 0.68x - 0.78y = 0.71x - 0.90y = 0.70x - 0.91y = 0.77x - 1.06y = 0.82x - 1.25
0.4
0.5
0.6
0.7
0.8
0.9
1
1.9 2.1 2.3 2.5 2.7
Patchen DET_OUT Voltage (x/6420)
OS
U N
DV
I
33873386338834933385
Sensor to sensorSensor to sensorvariability largevariability large
Patchen - NDVI CalibrationPatchen - NDVI Calibration
Field of View Issues -Field of View Issues - Fixed Detection ThresholdFixed Detection Threshold
Background affects Background affects weed detection errorweed detection error
0
10
20
30
40
50
0.0 2.0 4.0 6.0 8.0
Bindweed Coverage (%)
Err
or
at T
hre
sho
ld (
%)
All Data
Dry Soil
Moist Soil
1% detection error, requires 26% plant coverage5% detection error, requires 12 % plant coverage
Weed Detection Error When the Threshold Weed Detection Error When the Threshold is Adjusted for Changing Soil Backgroundis Adjusted for Changing Soil Background
WWeeeedd CCoovveerr((%% FFiieelldd--ooff--VViieeww))
DDeetteeccttiioonn EErrrroorr((%%))
66..00 00
33..00 00
22..00 22
11..00 00
00..88 00
00..55 00
Methods for Compensating for Methods for Compensating for Changing BackgroundChanging Background
• Periodic, manual Periodic, manual recalibration (current recalibration (current Patchen strategy).Patchen strategy).
• Reduce field-of-view to the Reduce field-of-view to the size where it will always size where it will always distinguish weeds from soil distinguish weeds from soil (fixed threshold).(fixed threshold).
• Build automatic adaptive Build automatic adaptive thresholding into the sensor.thresholding into the sensor.
OSU/NTech SensorOSU/NTech Sensor
Target
NIR and REDModulated
Illumination
Direction
Detection ofReflected
NIR and RED+Sun
GreenSeeker SensorGreenSeeker Sensor
• NDVI is independent of ambient temperatureNDVI is independent of ambient temperature• Sensor can operate 32 to 48 inches above the Sensor can operate 32 to 48 inches above the
targettarget• Sensor can control 3 or more valvesSensor can control 3 or more valves• Calibration curves can be downloaded to the Calibration curves can be downloaded to the
sensor.sensor.• The sensor can transmit NDVI readings and valve The sensor can transmit NDVI readings and valve
settings through the CAN network to a central settings through the CAN network to a central computercomputer
OSU/NTech OSU/NTech GGREENREENSSEEKEREEKERTMTM ApplicatorApplicator
• Sense and treat each 2 ft by 2 ft areaSense and treat each 2 ft by 2 ft area• Apply one of seven fertilizer rates Apply one of seven fertilizer rates
based on the crops yield potentialbased on the crops yield potential• Accomplish this while driving 15 Accomplish this while driving 15
mphmph• Operate day or nightOperate day or night• Provide the capability to detect and Provide the capability to detect and
treat other plant problemstreat other plant problems• Record and georeference sensor Record and georeference sensor
data for GIS analysisdata for GIS analysis• Sense and spot spray weeds (current Sense and spot spray weeds (current
Patchen technology)Patchen technology)
Sensor ElectronicsSensor Electronics
Oscillator(40 kHz)
CurrentDriver
Red LEDlight
production
CurrentDriver
NIR LEDlight
production
LED lightdetector
Reflectedlight
detector
MultiplexerBand-pass
filterand Amp
A/Dconversion
Micro-Micro-processorprocessor
CAN CAN NetworkNetwork
Valve Control Valve Control ModuleModule
UserInterfaceUI-ECU
PressureControlPC-ECU
Plant SensorSEN_ECU1
8
Plant SensorSEN_ECU1
7
Plant SensorSEN_ECU1
6
Plant SensorSEN_ECU3
0
Plant SensorSEN_ECU3
Plant SensorSEN_ECU2
Plant SensorSEN_ECU1
Plant SensorSEN_ECU1
5
NozzleAngleECU
BoomHeightECU
DiagnosticConnector
Terminator
HeightSensor #1
Terminator
Terminator
Terminator
VCM
VCM
VCM
VCM
VCM
VCM
VCM
VCM
UserInterfaceUI-ECU
PressureControl
PC-ECU
Plant SensorSEN_ECU18
Plant SensorSEN_ECU17
Plant SensorSEN_ECU16
Plant SensorSEN_ECU30
Plant SensorSEN_ECU3
Plant SensorSEN_ECU2
Plant SensorSEN_ECU1
Plant SensorSEN_ECU15
DiagnosticConnector
Terminator
Terminator
Terminator
RADAR
GPS
ValveControlModule
ValveControlModule
ValveControlModule
ValveControlModule
ValveControlModule
ValveControlModule
ValveControlModule
ValveControlModule
Joystick
Valves Available for Precision Valves Available for Precision ApplicationApplication
• Several different kindsSeveral different kinds– Solenoid/Diaphragm controlled valves (Capstan, Solenoid/Diaphragm controlled valves (Capstan,
Patchen, etc.).Patchen, etc.).– Pneumatic/Solenoid controlled valves (OSU).Pneumatic/Solenoid controlled valves (OSU).– Pintle and valve seat in spray solution (Detect Spray).Pintle and valve seat in spray solution (Detect Spray).
1. 1. All valves can only be operated on or off.All valves can only be operated on or off.
2. Both valve types can be pulse width modulated to2. Both valve types can be pulse width modulated to vary application rate without affecting distribution. vary application rate without affecting distribution.
3. There are no valves available the can be3. There are no valves available the can be continuously varied without affecting distribution. continuously varied without affecting distribution.
Tri-valve Set for Varying RateTri-valve Set for Varying Rate
• Stepped rates -Stepped rates -1x, 2x, 3x, 4x, 5x, 1x, 2x, 3x, 4x, 5x, 6x, 7x and off6x, 7x and off
• Can treat 0.6 by Can treat 0.6 by 0.6 m area 0.6 m area applying the target applying the target rate on 85% of that rate on 85% of that areaarea
BOOM PLUMBING LAYOUTBOOM PLUMBING LAYOUT
Units are in inches.
Forward directionForward direction
Farmer CheckNon-N Limiting
RI = 0.7/0.5 = 1.46RI = 0.7/0.5 = 1.46
In-Season Response Index (RINDVI)
ratefield
itingNnonNDVI NDVI
NDVIRI lim
Non-N-Limiting and Field Rate StripsNon-N-Limiting and Field Rate Strips7
10
5
20
3
30
1
39
9
49
7
59
5
69
3
79
1
88
9
98
7
10
85
11
83
12
81
13
79
14
77
15
75
1
15
29
43
57
Distance, ft
0.9-1
0.8-0.9
0.7-0.8
0.6-0.7
0.5-0.6
0.4-0.5
0.3-0.4
0.2-0.3
0.1-0.2
0-0.1
OSU/GreenSeeker Unit 1OSU/GreenSeeker Unit 1 N-Fertilizer Applicator N-Fertilizer Applicator