In the first year of this project (4th quarter), we evaluated the performance of a ground penetrating radar (GPR) to map root architecture of HLB-infected citrus trees, investigated the influence of several factors on the accuracy of the GPR system and developed an enclosure unit for the GPR for remote control of the system. The use of GPR system was a non-destructive approach to map tree roots without having any effect on the roots and the root-soil envronment. It can provide a rapid technique for root mapping. The GPR system consisted of two ground penetrating radar units with frequencies of 900 MHz and 1,600 MHz (TRU Model, Tree Radar Inc., USA) connected to a mobile scanning cart that had a control unit mounted on it which collected the data being sent from the radar and generated root morphology and root density maps. Additionally, a commercial software (TreeWin roots) was used to generate 3D root maps. In the initial evaluation of the system, we found that the GPR unit with 1,600 MHz frequency was more accurate in detecting root location and depth than the GPR unit with 900 MHz frequency. We have also found that the GPR system can distinguish between live and dead roots which is a very important aspect for studying the effects of diseases on citrus tree root systems.
In the first phase, we have investigated the influence of several factors on the accuracy of the GPR system. These factors were: (i) GPR Frequency; (ii) root diameter; (iii) root moisture level; (iv) root depth; (v) root spacing; (vi) survey angle; and (vii) soil moisture level. Experiments were conducted at the citrus research grove of the University of Florida Southwest Florida Research and Education Center (SWFREC) in Immokalee, USA. Upon conducting these experiments, we have found that the GPR can detect a root successfully when the root diameter is more than 6 mm. If two or more roots are in close proximity, the GPR system can only distinguish between them when the distance is more than 10 cm. We summarized all the results of these experiments and prepared a manuscript which we submitted for peer-review to the Agronomy Journal, Special Issue of Precision Agriculture. It was accepted and published:
“Zhang X., Derival M., Albrecht U., and Ampatzidis Y., 2019. Evaluation of a Ground Penetrating Radar to Map Root Architecture of HLB-infected Citrus Trees. Agronomy (Special Issue: Precision Agr.), 9(7), 354. https://doi.org/10.3390/agronomy9070354.”
Received: 3 May 2019 / Revised: 23 June 2019 / Accepted: 1 July 2019 / Published: 3 July 2019.
We have acknowledged CRDF: “Funding: This research was funded by the University of Florida Citrus Initiative and the Citrus Research and Development Foundation.”
In the second phase, we started developing an automated platform for the GPR system. In the current conditions, the operator has to manually go around the trees making very accurate 360-degree peripheral scans while maintaining a constant distance from the tree trunk. This process is time consuming and prone to manual measurement errors. The automated platform will help in eliminating this manual measurement errors thereby increasing the accuracy of the system and also reducing the amount of time taken for data collection. For the first prototype, we designed and built an enclosure unit for the radar unit which will allow the operator to control it remotely. We used 3D printed wheels which were connected to dual channel motor drivers; these motor drivers are remotely controlled by an 8-channel transmitter. Although the enclosure unit worked well on a regular terrain, it failed to make smoother movements of the soil. Hence, we worked on building a different enclosure unit; this time with an agile tracked chassis that is capable of efficient movement on even an irregular terrain. The new enclosure unit works well and can be efficiently used for the remote control of the GPR. We are currently working on developing the adjustable arm that can be used to connect the GPR to the trees which will help it make almost perfect 360-degree peripheral scans around the tree.
Our next objectives are:
(i) To complete the development of adjustable arm connection for GPR to citrus trees.
(ii) Evaluate the remote-controlled prototype in the field and compare it to the manual operation of the GPR system.