1 / 31

Optical-Sensors

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.

beate
Download Presentation

Optical-Sensors

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Optical-Sensors

  2. 0.50 Visible Light Near Infrared 0.25 % Reflectance 450 550 650 750 850 950 1050 Wavelength nm

  3. Example Index: Rred / Rnir Spectral shift in illumination prevents use of simple irradiance sensing Irradiance Sensing Strategies

  4. Reflectance Sensing Strategies Red Reflectance: r = Rred / Ired Reflectance is primarily a function of target

  5. - NIR Re d ± ± 780 6 nm 670 nm = NDVI + NIR Re d ± ± 780 6 nm 670 nm Normalized Difference Vegetative Index (NDVI)

  6. NIR Re d - Re flected Re flected NIR NIR = NDIV Inicident Incident Re flec tan ce NIR Re d + Re flected Re flected NIR NIR Inicident Incident Reflectance NDVI

  7. Light source is free. 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. Natural Lighting Advantages Limitations

  8. OSU Reflectance Sensor

  9. Artificial Lighting • Patchen high frequency pulsed narrow spectra lighting • Broad spectra lighting with filters • Constant or • Pulsed

  10. Removes the effect of changing background illumination. Can be operated 24 hours/day. 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. Artificial Lighting

  11. Patchen Weedseeker Optical Sensor

  12. Patchen Sensing Technique

  13. Patchen Sensing Technique

  14. Patchen Sensor NDVI Calibration 1 0.9 0.8 Good calibration to NDVI after filtering OSU NDVI 0.7 0.6 y = 0.7711x - 1.0618 0.5 0.4 1.9 2.1 2.3 2.5 2.7 Patchen DET_OUT Voltage (x/6420)

  15. Patchen Temperature Calibration Temperature drift unacceptable for absolute measurements

  16. Patchen - NDVI Calibration Sensor to sensor variability large

  17. Field of View Issues - Fixed Detection Threshold Background affects weed detection error 1% detection error, requires 26% plant coverage 5% detection error, requires 12 % plant coverage 50 40 All Data Dry Soil 30 Moist Soil Error at Threshold (%) 20 10 0 0.0 2.0 4.0 6.0 8.0 Bindweed Coverage (%)

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

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

  20. OSU/NTech Sensor

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

  22. OSU/NTech GREENSEEKERTM Applicator • Sense and treat each 2 ft by 2 ft area • Apply one of seven fertilizer rates based on the crops yield potential • Accomplish this while driving 15 mph • Operate day or night • Provide the capability to detect and treat other plant problems • Record and georeference sensor data for GIS analysis • Sense and spot spray weeds (current Patchen technology)

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

  24. Valves Available for Precision Application • Several 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.

  25. Tri-valve Set for Varying Rate • Stepped 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 area

  26. BOOM PLUMBING LAYOUT Forward direction Units are in inches.

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

  28. Non-N-Limiting and Field Rate Strips

  29. OSU/GreenSeeker Unit 1 N-Fertilizer Applicator

More Related