State of Engineering in Precision Agriculture, Boundaries and Limits for Agronomy

Topics 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

Spectra 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 nm Visible Light Near Infrared % Reflectance

Interfering Inputs: Soil Reflectances - Oklahoma

Reflectance and Vegetative Indices 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

NDVI Normalized Difference Vegetative Index Developed as an irradiance Index for remote sensing Varies from -1 to 1 Soil NDVI = to.05 Plant NDVI = 0.6 to 0.9 Typical plants with soil background NDVI= NDVI from different sources vary –Bandwidths for Red, NIR vary –Irradiance vs. reflectance based

Illumination Source Natural (Sunlight) Lighting – Passive Sensor Or Self Contained Lighting – Active Sensor

Passive Sensors Multi or Hyper Spectral Multi- Spectral Sense two or more wave lengths Measure both incident and reflected light Or Corrects 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 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 Sensor Measures many (100’s) of band Spectrometer (with integrating sphere for corn) Prototype sensor for scanning by Holland Scientific

Active 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

Sensing Technique

Height 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 Conversion 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 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 Rate 8 Stepped rates –OFF to 7x Treats 24”x 24” area applying the target rate on 85% of that area ValveRate 1x2x4xTotal x 2x 4x

Sensor Function