State of Engineering in State of Engineering in Precision Agriculture, Precision Agriculture,

Boundaries and Limits for Boundaries and Limits for AgronomyAgronomy

TopicsTopics

• Spectra• Sensors

– No. of Wave Lengths– Measurement units– Lighting Source– Field of View– Sampling Time– Range of Height

• Mechanisms for Variable Rate Application– Effect of treatment resolution– Available Mechanisms

SpectraSpectra

• Remote sensed electromagnetic radiation in the visible and near infrared bands– Sensors that work outside of that range are not

useful for sensing and variable rate application because of cost, difficulty in manufacturing and operating in a production agriculture environment.

• There are other sensors that may be of value, but the vast majority of the research to date has been with optical sensors.

Wavelength nmWavelength nm

Visible Visible LightLight

Visible Visible LightLight Near InfraredNear Infrared

450450 550550 650650 750750 850850 950950 10501050

0.250.25

0.500.50%

Ref

lect

ance

% R

efle

ctan

ce

550 650450

Interfering Inputs:Interfering Inputs:Soil 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.

Reflectance and Vegetative Reflectance and Vegetative IndicesIndices

• We normally do not use absolute measurements of the reflected light.

• To minimize the effects of variation in the sources of illumination all data must be normalized by dividing the magnitude of the reflected light by the incident light Reflectance.

• Measurements are generally presented in the form of vegetative indices, which are associated with plant properties

NDVINDVI

• Normalized Difference Vegetative Index

• Developed as an irradiance Index for remote sensing• 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

• NDVI from different sources vary– Bandwidths for Red, NIR vary– Irradiance vs. reflectance based

REDNIR

REDNIRNDVI

Illumination SourceIllumination Source

• Natural (Sunlight) Lighting – Passive Sensor OrSelf Contained Lighting – Active Sensor

Passive SensorsPassive Sensors

• Multi or Hyper Spectral• Multi- Spectral Sense two or more wave lengths• Measure both incident and reflected light

OrCorrects be regularly measuring light reflected from a “White” plate

• Generally uses Band Pass or Interference optical filters

• Commercially available as a sensor/applicator from Hydro

• 4 Band sensor being built by Holland Scientific

Passive SensorsPassive Sensors

• Satellites such as IKONIS, LandSat, and Quickbird all provide multispectral imagery

• There a number of sources of aircraft based imaging cameras

• There are digital cameras (e.g. DuncanTech) the can be mounted on aircraft or ground-based vehicles at a “reasonable” cost

Hyper-Spectral SensorHyper-Spectral Sensor

• Measures many (100’s) of band• Spectrometer (with integrating sphere for

corn)• Prototype sensor for scanning by Holland

Scientific

Active Lighting SensorsActive Lighting Sensors

• Uses self-contained illumination, usually high intensity LED’s

• Wave lengths are limited to available LED’s• Uses high frequency (approximately 40,000

cycles per second) light which enables the electronics to filter out background (sunlight). Measurements are independent of the background illumination.

• Currently limited to 2 bands, e.g. 670 and 780 nm or 550 and 780 nm

Crop Target

NIR and REDModulated

Illumination

Direction

Sensing TechniqueSensing TechniqueDetection of

ReflectedNIR and RED

+Sun

HeightHeight

• The size of the field of view of all sensors is affected by the height above the target

• Within a limited range it is possible to minimize the effect of the height.– GreenSeeker uses masks to maintain a

constant field of view from a height of 32 to 48 inches above the target.

• Field of View size ranges from 30 by 30 m (LandSat TM) to 0.5 by 24 inches (GreenSeeker)

Sensor Sampling or Sensor Sampling or Conversion TimeConversion Time

• All digital optical sensors require a finite amount of time to convert measurements to a digital format and to store the data.

• This may range for one second or more for a digital camera to less than 0.1 s for the GreenSeeker sensor.

• The combination of the sampling time and the vehicle speed dictate the “length” of the field of view.

Variable Rate ApplicatorsVariable Rate Applicators

• I am not aware of any granular applicators that can provide the distribution patterns and response time needed to do high speed variable rate application of nitrogen or other fertilizers.

• Anhydrous ammonia – Kansas State University/Capstan Corporation

• Liquid fertilizers

Tri-valve Set for Varying RateTri-valve Set for Varying Rate

• 8 Stepped rates– OFF to 7x

• Treats 24”x 24” area applying the target rate on 85% of that area

Valve Rate

1x 2x 4x Total

0 0 0 0

1 0 0 1

0 2 0 2

1 2 0 3

0 0 4 4

1 0 4 5

0 2 4 6

1 2 4 7

1x 2x 4x

Sensor FunctionSensor Function

Lightgeneration

Light signal

Lightdetection

Valve settings Calculate NDVI Lookup valve setting Apply valve setting Send data to UI

“Sensor”Valves

andNozzles