Optical-Sensors

Wavelength nm Visible Light Near Infrared % Reflectance

Irradiance Sensing Strategies Spectral shift in illumination prevents use of simple irradiance sensing Example Index: R red / R nir

Red Reflectance: r = R red / I red Reflectance is primarily a function of target Reflectance Sensing Strategies

nm670nm6780 nm670nm6780 dReNIR dReNIR NDVI      Normalized Difference Vegetative Index (NDVI)

Incident flectedRe Inicident flectedRe Incident flectedRe Inicident flectedRe cetanflecRe NIR dRe NIR dRe NIR NDIV    Reflectance NDVI

Natural Lighting Light source is free.Light source is free. Much of the effect of spectral shift can be corrected by measuring incident and reflected. light and calculating reflectance.Much of the effect of spectral shift can be corrected by measuring incident and reflected. light and calculating reflectance. Spectral shifts occur as sun angle changes. Cloud cover affects intensity. Moisture and dust cause differences in refraction and absorbence across the spectra. Can’t be operated at night. AdvantagesLimitations

OSU Reflectance Sensor

Artificial Lighting Patchen high frequency pulsed narrow spectra lightingPatchen high frequency pulsed narrow spectra lighting Broad spectra lighting with filtersBroad spectra lighting with filters –Constant or –Pulsed

Artificial Lighting Removes the effect of changing background illumination.Removes the effect of changing background illumination. Can be operated 24 hours/day.Can be operated 24 hours/day. Can produce an absolutely calibrated signal.Can produce an absolutely calibrated signal. Choice of spectral bands are limited when pulsed solid state lighting sources (LED’s or lasers) are used. Broadband lighting requires high power. Cost of the sensor/lighting systems are higher than those using natural lighting.

Patchen Weedseeker Optical Sensor

Patchen Sensing Technique

Patchen Sensor NDVI Calibration y = x Patchen DET_OUT Voltage (x/6420) OSU NDVI Good calibration to NDVI after filtering

Temperature drift unacceptable for absolute measurements Patchen Temperature Calibration

Sensor to sensor variability large Patchen - NDVI Calibration

Field of View Issues - Fixed Detection Threshold Fixed Detection Threshold Background affects weed detection error Bindweed Coverage (%) Error at Threshold (%) All Data Dry Soil Moist Soil 1% detection error, requires 26% plant coverage 5% detection error, requires 12 % plant coverage

Weed Detection Error When the Threshold is Adjusted for Changing Soil Background

Methods for Compensating for Changing Background Periodic, manual recalibration (current Patchen strategy).Periodic, manual recalibration (current Patchen strategy). Reduce field-of-view to the size where it will always distinguish weeds from soil (fixed threshold).Reduce field-of-view to the size where it will always distinguish weeds from soil (fixed threshold). Build automatic adaptive thresholding into the sensor.Build automatic adaptive thresholding into the sensor.

OSU/NTech Sensor

GreenSeeker Sensor NDVI is independent of ambient temperatureNDVI is independent of ambient temperature Sensor can operate 32 to 48 inches above the targetSensor can operate 32 to 48 inches above the target Sensor can control 3 or more valvesSensor can control 3 or more valves Calibration curves can be downloaded to the sensor.Calibration curves can be downloaded to the sensor. The sensor can transmit NDVI readings and valve settings through the CAN network to a central computerThe sensor can transmit NDVI readings and valve settings through the CAN network to a central computer

OSU/NTech G REEN S EEKER TM Applicator OSU/NTech G REEN S EEKER TM Applicator 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 based on the crops yield potentialApply one of seven fertilizer rates based on the crops yield potential Accomplish this while driving 15 mphAccomplish this while driving 15 mph Operate day or nightOperate day or night Provide the capability to detect and treat other plant problemsProvide the capability to detect and treat other plant problems Record and georeference sensor data for GIS analysisRecord and georeference sensor data for GIS analysis Sense and spot spray weeds (current Patchen technology)Sense and spot spray weeds (current Patchen technology)

Sensor Electronics Oscillator (40 kHz) Current Driver Red LED light production Current Driver NIR LED light production LED light detector Reflected light detector Multiplexer Band-pass filter and Amp A/D conversion Micro- processor CAN Network Valve Control Module

Valves Available for Precision Application Several different kindsSeveral different kinds –Solenoid/Diaphragm controlled valves (Capstan, Patchen, etc.). –Pneumatic/Solenoid controlled valves (OSU). –Pintle and valve seat in spray solution (Detect Spray). 1. All valves can only be operated on or off. 2. Both valve types can be pulse width modulated to vary application rate without affecting distribution. 3. There are no valves available the can be continuously varied without affecting distribution.

Tri-valve Set for Varying Rate Stepped rates - 1x, 2x, 3x, 4x, 5x, 6x, 7x and offStepped rates - 1x, 2x, 3x, 4x, 5x, 6x, 7x and off Can treat 0.6 by 0.6 m area applying the target rate on 85% of that areaCan treat 0.6 by 0.6 m area applying the target rate on 85% of that area

BOOM PLUMBING LAYOUT Units are in inches. Forward direction

Farmer Check Non-N Limiting RI = 0.7/0.5 = 1.46 In-Season Response Index (RI NDVI )

Non-N-Limiting and Field Rate Strips

OSU/GreenSeeker Unit 1 N-Fertilizer Applicator