J. D. Whitney

Investigation of Laser and Ultrasonic Ranging Sensors for Measurements of Citrus Canopy Volume

This study compared ultrasonic and laser measurements of citrus canopy volume with manual measurement methods. Fifteen trees with different canopy heights and volumes were used. Manual and ultrasonic measurements provided dimensions for computing the canopy volume whereas laser measurements gave information that could be used to compute a ‘laser canopy volume index.’ Ultrasonic and laser methods agreed with manual methods (R 2 > 0.85, RMSE < 2.15 m 3 ). Laser showed better prediction of canopy volume than the ultrasonic system because of the higher resolution. Ultrasonic or laser sensors can be used for automatic mapping and quantification of the canopy volumes of citrus trees.

Low-cost automatic yield mapping in hand-harvested citrus

A simple system has been developed to generate yield maps of hand-harvested citrus in a reliable, low-cost manner using a commercial GPS recorder. Individual 0.7-m3 container locations are mapped to indicate yield variations within a citrus block. Further future refinements are discussed. The system is applicable to other manually harvested crops and harvesting systems.

PRECISION FARMING APPLICATIONS IN FLORIDA CITRUS

A cooperative effort between researchers, manufacturers, and growers has been investigating precision farming applications in Florida citrus. Citrus yields, based on the location of volume-based containers, were mapped using a conventional fruit-loading truck, manual harvesters (> 99% of Florida citrus is manually harvested), and GIS/GPS components. These maps were overlaid on geo-referenced aerial photographs of the tree canopies. Two fruit weighing systems were mounted on a fruit-loading truck and integrated with the GIS/GPS components to investigate mapping weight-based yields. Results to date indicate the truck-mounted weighing systems were within 1 to 6% of certified scale weights on 20 t loads of fruit. Electronically recording harvester identity is being integrated with yield mapping to make the entire system more reliable and attractive to harvesters and growers.

Evaluation of Methodologies for Field Studies of Spray Deposition

ABSTRACT USING Rhodamine-B and copper as tracers, four common methods of deposition assessment, i.e., combinations of fluorometry and colorimetry on leaf and mylar targets were compared for use on citrus. Merits and limitations of each method were identified. All were found to be reliable; however, considering limitations in the lab and in the field, colorimetric analysis of leaf samples appeared to be the most desirable method for deposition or residue assessment in citrus spraying.

A DGPS YIELD MONITORING SYSTEM FOR FLORIDA CITRUS

A yield monitoring system was developed based on a differential global positioning system (DGPS) and three fruit weighing systems. The DGPS unit eliminated post processing of the data and provided accurate location of fruit containers used in conventional manual harvesting. Three DGPS units did not vary significantly when comparing position accuracy. The weighing systems consisted of a pressure transducer mounted in the pressure line of the truck bed lifting cylinder, a system with four load cells under the four corners of the truck bed, and a single load cell in the loader boom. On trailer loads of fruit, the most to least accurate system was the lift cylinder (~1% error), the loader boom (<2% error), and the load cells (~5% error). On individual pallet bin loads of fruit, however, the coefficients of variation for the lift cylinder, loader boom, and load cells were 15, 6, and 25%, respectively.

GROUND SPEED EFFECT ON SPRAY DEPOSITION INSIDE CITRUS TREES

ABSTRACT The effects of sprayer ground speed (1.6-6.4 km/h) on spray deposition at different locations within citrus tree canopies was characterized using different airblast sprayers, tree types, and sampling methodologies, in two spray tests carried out in Florida citrus. Copper hydroxide with 50% metallic copper was applied as a tracer. Cotton ribbons and citrus leaves were used as sampling targets and deposition was determined by copper colorimetry. Ground speed did not have a significant effect on mean deposition in the tree canopy; however, variability of deposition increased as speed increased. Sample location had a significant effect on spray deposition and showed significant interactions with speed.

DEVELOPMENT AND TESTING OF A CITRUS YIELD MONITOR

Site–specific monitoring of citrus yield is important in understanding yield variability and its causes. A microcontroller–based system was designed to automatically monitor citrus yield harvested into individual tubs. The microcontroller was interfaced with a differential global positioning system (DGPS), a flash memory key, two limit switches, a buzzer, and a counter, which provided position information, storage, triggering, acknowledgement, and counting, respectively. The microcontroller system was mounted on a special truck (goat) that handles fruit and fruit tubs in the groves. The system was designed such that whenever the fruit was dumped into the truck bed, DGPS information was acquired and the counter and buzzer were triggered. The position information was then stored into a flash key and later downloaded to a personal computer for data analysis and mapping. This article details the design and evaluation of the citrus yield monitoring system. The evaluation phase showed that the system was able to detect the dumping events and store the DGPS locations, 100 and 98% of the time, respectively.

EVALUATION OF WEIGHING SYSTEMS FOR CITRUS YIELD MONITORING

Three electronic sensor systems were installed and evaluated to measure citrus yield at the grove level. All systems were integrated as a part of a specialized vehicle, known as a “goat”, which is used for Florida citrus to transfer fruit from grove to road side. The first system consisted of four load cells which measured the bed weight of the harvesting vehicle as each bin or tub of fruit was placed on it. The second system consisted of a load cell attached to the hydraulic arm of the vehicle which recorded pallet bin or tub weight. The third system measured the hydraulic pressure in the vehicle’s bed lift. These sensor systems were interfaced to a field GPS and A/D data acquisition unit. Comparative data are presented for the performance of each unit and resultant overall system accuracy. Limitations observed in field trials are detailed where overall error rates were <6% compared to truck scale readings..

Dynamic analysis of a trunk shaker-post system.

ABSTRACT Dynamic properties of a wooden post (viscous damping, mass, and stiffness) were measured and used along with corresponding characteristics of a shaker (unbalanced mass, total mass, eccentricity, and frequency of rotation) in the development of a mathematical model to predict applied shaker force and motion. Three lengths of a wooden post were cantilever supported in a concrete base structure and shaken with an inertia-type linear trunk shaker. Motion and force at the point of attachment were measured and analyzed. Predominate components of the system were generated force, total shaker mass, and post stiffness. Measured force and motion data were used to calculate an effective post stiffness. Force and displacement amplitudes and post stiffness predicted by the model agreed reasonably well with measured values.

Optimizing Orange Grove Factors for Fruit Production and Harvesting

Ten hectares of oranges were planted in 1980 in an experiment to investigate optimal management practices for different tree spacings, scion, and rootstock combinations. Experimental factors included two between-row spacings (6.0, 4.5 m), two in-row spacings (4.5, 2.5 m), two scions (‘Hamlin’, early season; ‘Valencia’, late season), two rootstocks (Milam, vigorous; Rusk citrange, moderately vigorous), and two tree heights (3.7, 5.5 m).