Huanglongbing (citrus greening) detection using visible, near infrared and thermal imaging techniques

This study demonstrates the applicability of visible-near infrared and thermal imaging for detection of Huanglongbing (HLB) disease in citrus trees. Visible-near infrared (440-900 nm) and thermal infrared spectral reflectance data were collected from individual healthy and HLB-infected trees. Data analysis revealed that the average reflectance values of the healthy trees in the visible region were lower than those in the near infrared region, while the opposite was the case for HLB-infected trees. Moreover, 560 nm, 710 nm, and thermal band showed maximum class separability between healthy and HLB-infected groups among the evaluated visible-infrared bands. Similarly, analysis of several vegetation indices indicated that the normalized difference vegetation index (NDVI), Vogelmann red-edge index (VOG) and modified red-edge simple ratio (mSR) demonstrated good class separability between the two groups. Classification studies using average spectral reflectance values from the visible, near infrared, and thermal bands (13 spectral features) as input features indicated that an average overall classification accuracy of about 87%, with 89% specificity and 85% sensitivity could be achieved with classification models such as support vector machine for trees with symptomatic leaves

M-statistic obtained for the best VI in each field.

<p>The values given in bold represent the vegetation indices that achieve values >1.3 in all locations, except COMB 1 in Field A.</p><p>M-statistic obtained for the best VI in each field.</p

False color aerial image captured in Field D.

<p>The circles in green color represent avocado trees showing advantage stage symptoms of laurel wilt disease. The circles in blue color represent avocado trees with initial symptoms of laurel wilt affection.</p

Location of the study area in Florida State and Miami Dade County.

<p>Location of the study area in Florida State and Miami Dade County.</p

Box plot showing variation in vegetation index selected for healthy and laurel wilt affected plants.

<p>Box plots followed by different letter are significantly different according to Tukey HSD test at a 0.01 level of significance.</p

M-statistics obtained comparing laurel wilt and vines.

<p>The value given in bold represent the vegetation indices that achieve value >1.3</p><p>M-statistics obtained comparing laurel wilt and vines.</p

False color images of a) vines and b) fruit stress trees.

<p>The circles show details of represented factors and they are shown below in a zoom.</p