University of Florida

Wonsuk "Daniel" Lee

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Department of Agricultural and Biological Engineering
207 Frazier Rogers Hall, PO Box 110570 Gainesville, FL 32611
352-392-1864 ext. 207

At the heart of Wonsuk "Daniel" Lee's expertise is the application of sensors, devices which "see" beyond the range of human senses and can deliver information to computers and other devices. Lee's skills also include a wide range of supporting technologies and novel applications, such as GPS, geographic information systems, machine vision, image processing, spectroscopy, automation and machine systems design. He draws from all these areas to develop solutions for a wide range of agricultural problems.

Currently, Lee is working on one of the major challenges to the Florida citrus industry, a disease called citrus greening. The disease gets this name from the greenish patches on infected fruit. The disease also causes a characteristic yellowing along the veins of leaves and was called huanglongbing (HLB) or Yellow Dragon Disease in China, where it was first described in the early twentieth century. Citrus greening or HLB is known in every place that produces citrus.

Citus greening is caused by a bacterium called Candidatus Liberibacter, which is carried from tree to tree by a very small fly called a psyllid. Psyllids live by sucking the juices from plants, and usually they live off only one kind of plant. Infected trees become yellowish and unhealthy. They tend to drop their leaves, and if they produce fruit, it is likely to be misshapen, discolored, and bitter tasting. The disease progresses until it kills the entire tree.

Grove owners employ inspectors who check their trees every few months and look for signs of the disease. If an infected tree is found, it is cut down, removed from the grove and burned. The inspection process is labor-intensive and expensive. Also, fatigue becomes a factor in the accuracy of the inspector's work day progresses. Effective inspection is critical for keeping citrus greening from destroying Florida's citrus industry, but keeping growers' costs down is also important if Florida oranges are to remain competitive in the marketplace.

Lee would like to improve the accuracy and speed of the inspection process and save growers money by applying his knowledge of sensors and information processing to this problem. He is currently working on a system which uses a camera attached to an airplane that can be flown over the groves to collect images of trees. The camera and the images it captures are called hyperspectral because they can capture wavelengths of infrared and ultraviolet light, beyond what the human eye can see, in addition to visible light. Using computer analysis, Lee can examined these images at very specific wavelengths of light. He compared the light at these wavelengths from healthy and diseased trees, and he found definite differences.

Because there are differences, Lee believes a working system will be possible. It depends now on being able to develop a sufficiently accurate system. Lee says that the hyperspectral camera has a resolution of about two feet by two feet (0.7 m x 0.7 m). So it does not see individual fruit or leaves, but picks up signs of infection within trees. The system Lee has been testing has an accuracy of about 70% when compared to the results of ground-based inspectors. The remaining 30% includes both situations where the system failed to spot a diseased tree (false negative) and cases where the system thought a healthy tree was diseased (false positive). Lee is fine tuning the system by adding additional wavelengths to his computer analysis, and has high hopes of increased accuracy.

To gain a deeper insight into the disease itself, Lee is working with plant pathologists to understand the differences he sees. It appears that these differences arise from the increased amount of starch that the plants accumulate as a result of the disease. Understanding this mechanism in more detail can help Lee focus his efforts and increase the system's accuracy.

In another application of sensor technology for the citrus industry, Lee has been working to estimate automatically the amount of non-fruit plant material that is collected during citrus harvesting. Citrus fruits that are ready to harvest may detach from the tree easily or with difficulty. Whether manual or mechanical harvesting is used, a fair amount of plant material is collected along with the fruit. In the business, this extraneous plant material is called trash. Growers would like know how much of this trash is being collected, and they would also like to remove it automatically to save a step before the fruits are sent to the packing house, where they will be prepared for shipment and sale.

When citrus is harvested mechanically, it is dropped onto a flat-bed trailer the floor of which is a conveyor belt. The conveyor moves the fruit to the front of the trailer where a second conveyor lifts it up and dumps it into a bin. Rotating brushes snag trash and pull it down out of the stream of traveling oranges. This process moves very quickly, but Lee is developing a machine vision system that estimates the amount of trash using a computer to detect the colors and shapes of leaves and twigs. This system can also assist in detecting diseased materials and improving the automated trash removal mechanism.

While it is important to the growers to know the amount of trash, it is equally important to them to eliminate as much of the trash as possible before the oranges are collected. In this way, potentially diseased materials remain in the grove instead of being transported to processing facilities. This prevents the spread of plant diseases and reduces time and costs in processing. Another aspect of this system combines the estimation of trash with GPS coordinates so that growers can know the relative amounts of trash being generated in specific areas of their groves. The system can give them a "trash map" of their grove which can help them in adjusting their operations and understanding the condition of their trees.

Of course, citrus is just one of many important agricultural commodities produced in Florida, and Lee is looking at ways of extending the technologies he is developing to other crops. He recently attended a meeting of blueberry producers, horticulturists, soil scientists, plant pathologists, and engineers to begin looking at how precision agriculture could benefit blueberry production in Florida., other states, and Canada. Lee is already planning to use the machine vision/GPS system he developed for citrus to give blueberry producers maps of their fields that can tell how productive the various areas of a field are. This can give growers important information about what areas of a field need more or less water or nutrients. Instead of using a one-size-fits-all approach, growers can take a precision agriculture approach and adjust inputs according to the specific needs of individual regions of their fields. This approach can reduce the cost of inputs for the grower, as well as improving conservation efforts to reduce water use and contaminated runoff.