In the fifth quarter of this project, we started developing a new calibration system to get a better estimation of the depth of the roots when compared to the existing calibration methods. The existing calibration methods use dielectric constant measured using soil type and soil moisture level to get the depth of the roots. This new method combines dielectric constant calibration in the field with the post-processed data that is extracted in the lab. This method uses two different dielectric constant values at different depths, one at a deep level and another at a shallow level. These both values will be used to correct the GPR estimated depth of the root and increase the accuracy of root depth estimation. For evaluating this calibration method, we conducted field experiments at SWFREC citrus grove to determine: (i) effect of roots diameter on GPR depth measurement, (ii) effect of dielectric constant on GPR depth measurement and (iii) effect of root depth on GPR depth measurement. Upon performing these experiments, it is determined that the accuracy of depth of shallow roots was better than the depth of roots present at a deeper level and also, the new calibration method can be used to improve the accuracy of depth estimation for roots present at a level closer to the ground. We have found that this is due to the dielectric constant value being constant at shallow levels, because there is almost no change in the soil moisture content. However, as the depth increases, the soil moisture content rises and the dielectric constant increases, leading to the use of average value of all the changing dielectric constant values at deeper levels. All the results and discussion of these experiments are being prepared into a manuscript and will be reviewed further.We are also working on the development of an adjustable arm connection for the GPR to citrus trees. Several 3D modelled arms have been designed and are being tested to improve the functionality of the arm. The important functionality points we are considering implementing in the arm development is that (i) the arm fits all different tree sizes varying from young to old trees. (ii) the arm contains a measurement scale that can adjusted and fixed so that the 360 degree rotation around the tree remains constant at all time. In the coming quarters, we will:1) Develop further the new calibration method to improve the accuracy of depth estimation.2) Review the above mentioned manuscript containing results and discussion of the new calibration method and submit it for publication.3) Continue the development and testing of the automated GPR system to increase the efficiency of the system.