Abstract
Visible-near infrared (VIS-NIR) spectral data are widely used for remotely estimating a number of crop health metrics. In general, these indices and models do not explicitly account for leaf surface characteristics, which themselves can be indicators of plant status or environmental responses. To explicitly include leaf surface characteristics, data are required linking optical properties to surface characteristics. We present the design and experimental validation of a goniospectropolarimeter (GoSPo) that combines the capabilities of a spectrometer, goniometer, and polarimeter. GoSPo was designed with the objective of studying the relationships between leaf surface characteristics and the resulting light reflectance, transmission, and polarization as functions of both direction and VIS-NIR spectra. Using six motors, a pneumatic system, two spectrometers, and a combination of lenses, polarizers, and mirrors, GoSPo can examine a leaf from a particular angle, approximate hemispherical transmittance and reflectance (with root-mean-square error values of 0.0189 and 0.0216 for reflectance and transmittance, respectively, compared to a spectrophotometer and integrating sphere), and obtain spectral polarization measurements without disrupting the sample between measurements. The data collected with GoSPo will aid in model development for remote sensing applications.
Highlights
The spectral reflectance of plant leaves has been measured and modeled for decades to inform remote methods for monitoring vegetation health and plant status
To determine the effect of angular resolution at 1-deg and 5-deg sensor increments on reflectance and transmittance estimates, a 250-μm PTFE sheet was measured twice in GoSPo
The root-mean-square errors (RMSEs) values for transmittance were 0.1080, 0.0692, and 0.0082 for 1000, 500, and 250-μm-thick sheets, respectively. These results indicate that given the case of a symmetrical bidirectional reflectance distribution function (BRDF), using discrete measurements and integrating over the hemisphere can adequately approximate hemispherical reflectance and transmittance without the use of an integrating sphere
Summary
The spectral reflectance of plant leaves has been measured and modeled for decades to inform remote methods for monitoring vegetation health and plant status. The wide variability in surface property contributions to leaf reflectance is not explicitly or significantly accounted for in the most prevalent models.[1] Models based on directional measurements use hemispherical leaf measurements in calibration and development. This method is useful for analysis of individual leaf measurements in a laboratory setting and can be applied when averaging canopy angle, but as the spatial resolution of data improves and close-range multiangular modeling of leaf surface–light interactions have more potential value. GoSPo achieves some of the same goals of the previously designed apparatus, but expands the spectral range further into the near infrared (NIR) and allows for both polarized and nonpolarized measurements of both reflectance and transmittance without needing to reposition the sample
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
