Jay B. Fitzgerald

Calibration and use of a pyroelectric thermal camera and imaging system for greenhouse infrared heating evaluation

Abstract Infrared sensing instruments were calibrated and used to measure crop surface temperature distributions in a gas-fired, infrared heated greenhouse. These instruments included thermistors, narrow field of view infrared thermometers for small spot areas, and a pyroelectric thermal vision camera, equipped with a variable automatic gain to optimize the grey scale circuit. The thermal vision camera was used for both qualitative and quantitative temperature measurement by evaluating temperatures from crop images, using machine vision. Calibration was conducted using hot and cold reference surfaces of known temperature. Images were digitized with a computer and frame grabber, and analyzed with a commercial software package. Grey-scale values of the calibration surfaces correlated well (r2 = 0.98) with other corresponding temperature measurements. Crop surface temperature under radiant heating in a greenhouse was observed to be quite uniform ±2.5°C. Sources of radiant energy loss were identified in the greenhouse, operated at a suboptimal air temperature, for improved heating efficiency.

Simulated Water Use and Canopy Resistance of New Guinea Impatiens (Impatiens X hb.) in Single Pots Using Infrared Heating

A plant-based temperature, infrared thermometer (IRT) control system was tested for a prototype greenhouse infrared heating system, using water use and canopy resistance of New Guinea Impatiens as performance indicators. Infrared heaters were used to raise canopy temperature of New Guinea Impatiens to a literature-based optimum level, which resulted in higher daily water use than plants receiving no radiant heat. The increase in plant water use was proportional to the decrease in the leaf-air temperature difference. Plants with canopy temperature close to 24° C had increased water use of 118%, when air temperature was increased from 8° to 18° C, and 33% when the air temperature was increased to 24° C. A modified Monteith equation using canopy temperature predicted evapotranspiration very well, especially when the leaf-air temperature difference was 6° C or less. Canopy resistance values were predicted to be higher for heated plants at higher leaf-air temperature differences and vapor pressure deficits (VPD) using a separate canopy energy analysis.

Vision methods for inspection of greenhouse poinsettia plants

Various vision methods for inspecting the growth and quality of poinsettia plants are discussed in this paper . The visible and near-infrared vision approaches are based on previous spectral reflectance measurements . Low (0 ppm) nitrogen plants grown in a greenhouse showed an increase in red (0. 7 - 0. 75 rim) and a decrease in near-infrared ( 0 . 8 - 1 . 1 im) reflectance over high ( 256 ppm) nitrogen levels . Growth chamber plants showed similar reflectance in the red but different NIR reflectance than with greenhouse plants . NIR reflectance was affected by vegetative density and not by leaf nitrogen content. Thermal imaging techniques (12 - 14 im) improve canopy temperature measurements . The usefulness of image methods depends on reflectivity analog-digital sensitivity and background lighting quality. An electronic plant doctor based on a database of images would be a useful tool for the grower to perform visual diagnostics. 1.

Improved Instrumentation and Controls for Biomass Heating and Impact on Greenhouse Profitability

An adaptive real time crop and greenhouse model was implemented in a Nebraska commercial double-poly greenhouse during 2008 and 2009. Biomass heating using a pellet-burning furnace was alternated with a traditional propane heating system. Data collected included three spatial measurement zones within the greenhouse, including air and furnace temperatures, plant temperature, floor temperature, potting soil temperature, and inside roof glazing temperature using low-cost IRT/c sensors. Humidity, total and photosynthetically Humidity, total short wave radiation and photosynthetically active radiation (PAR) and the outside conditions were also measured. Ventilation fan, unit heater, and biomass burner operations were monitored with split core current sensors attached to the electric supply and control wires. National Instruments LabVIEW® software was developed to collect data and to report energy usage, moisture condensation potential, and production performance of the greenhouse. The zone loggers communicated using wireless technology with a master computer located at one end of the house. Moisture condensation potential on the leaves, floor, and inside glazing was continuously monitored throughout each day. Night time heat loss over the growing periods ranged from 25,000 to 160,000 BTU per hour. Greenhouse moisture condensation was found generally less for biomass than with the propane heating operation. Furnace performance was reported and a fuzzy logic control system is still being tested. Biofuel energy content was measured using an adiabatic bomb calorimeter. Considerable fuel savings were found possible with the system providing feedback to the grower.

Spatial statistical measures of crop temperature variability using infrared thermography in radiant heated greenhouse crops

Crop surface temperature under a radiant heated greenhouse was measured using a portable infrared thermometer. Plants were arranged so that each plant occupied a grid cell of 30 cm X 30 cm (1 ft X 1 ft). Data collected were analyzed for their spatial distribution. Geostatistical software was used to characterize the spatial variability of the plant surface temperature. The shape of the empirical semi-variogram suggested that a spherical model was best fitted to the empirical semi-variogram. This model indicated that the nugget effect was estimated at 1.2, the sill at 3.3 and the range at 1.65 m. This model was used in block kriging to estimate plant surface temperature for unsampled locations.

Simulated Water Use and Growth of New Guinea Impatiens (Impatiens X hb.) in Single Pots Using Root Zone Heating

Root zone heating on New Guinea impatiens (Impatiens X hb.) in single pots was evaluated under computer-controlled growth chamber conditions. The effects of root zone heating and air temperature on dry weight, fresh weight, leaf area (plant canopy temperature), and plant water use were determined. Measured plant water use correlated highly with plant dry matter production for both heated (r2 = 0.96) and controlled (r2 = 0.93) plants. Measured plant transpiration and evaporation rates compared favorably with values predicted by the Monteith evapotranspiration model (root-mean-square errors = 0.37 and 0.30 mm/day, respectively). Even when air temperatures were held around 128 C, a root temperature at 248 C increased plant dry matter. Total plant water use was significantly increased by higher root zone temperatures.