Response of spectral reflectances and vegetation indices on varying Juniper cone densities

Authors: PENG, D. - Chinese Academy Of Sciences; JIANG, Z. - University Of Arizona; HUETE, A.R. - University Of Technology Sydney; Ponce Campos, Guillermo; NGUYEN, U. - University Of Arizona; LUVALL, J.C. - National Aeronautics Space Administration (NASA) - Jet Propulsion Laboratory

Submitted to: Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2013
Publication Date: 10/22/2013
Citation: Peng, D., Jiang, Z., Huete, A., Ponce Campos, G.E., Nguyen, U., Luvall, J. 2013. Response of spectral reflectances and vegetation indices on varying Juniper cone densities. Remote Sensing. 5:5330-5345. https://doi.org/10.3390/rs5105330.
DOI: https://doi.org/10.3390/rs5105330

Interpretive Summary: Juniper trees species are well known as common sources of allergies due to the microscopic pollen grains released and then transported by wind and inhaled by humans. This work shows an analysis of the spectral influences of pollen discharging male juniper cones within a juniper canopy. In general, within the electromagnetic spectrum analyzed, narrowband reflectances were more sensitive to cone density changes than the equivalent MODIS broadbands. Vegetation indexes showed a significant relationship with cone density levels, particularly with the narrowband versions and the two-band vegetation index (TBVI) based on Green and Red bands. Results indicate that data from sources like Phenocams can be used in Juniper trait studies that eventually can be used for juniper cone detection as a methodology to support public health applications.

Technical Abstract: Juniper trees are widely distributed throughout the world and are common sources of allergies when microscopic pollen grains are transported by wind and inhaled. In this study, we investigated the spectral influences of pollen discharging male juniper cones within a juniper canopy. This was done through a controlled outdoor experiment involving ASD FieldSpec Pro Spectroradiometer measurements over juniper canopies of varying cone densities. Broadband and narrowband spectral reflectance and vegetation index (VI) patterns were evaluated as to their sensitivity and their ability to discriminate the presence of cones. The overall aim of this research was to assess remotely sensed phenological capabilities to detect pollen-bearing juniper trees for public health applications. A general decrease in reflectance values with increasing juniper cone density was found, particularly in the Green (545–565 nm) and NIR (750–1,350 nm) regions. In contrast, reflectances in the shortwave-infrared (SWIR, 2,000 nm to 2,350 nm) region decreased from no cone presence to intermediate amounts (90 g/m2) and then increased from intermediate levels to the highest cone densities (200 g/m2). Reflectance patterns in the Red (620–700 nm) were more complex due to shifting contrast patterns in absorptance between cones and juniper foliage, where juniper foliage is more absorbing than cones only within the intense narrowband region of maximum chlorophyll absorption near 680 nm. Overall, narrowband reflectances were more sensitive to cone density changes than the equivalent MODIS broadbands. In all VIs analyzed, there were significant relationships with cone density levels, particularly with the narrowband versions and the two-band vegetation index (TBVI) based on Green and Red bands, a promising outcome for the use of phenocams in juniper phenology trait studies. These results indicate that spectral indices are sensitive to certain juniper phenologic traits that can potentially be used for juniper cone detection in support of public health applications.