Hybrid spatial-temporal Mueller matrix imaging spectropolarimeter for high throughput plant phenotyping

Authors: KUDENOV, MICHAEL - North Carolina State University; KRAFFT, DANNY - North Carolina State University; SCARBORO, CLIFTON - North Carolina State University; DOHERTY, COLLEEN - North Carolina State University; Balint-Kurti, Peter

Submitted to: Applied Optics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2023
Publication Date: 1/31/2023
Citation: Kudenov, M., Krafft, D., Scarboro, C., Doherty, C., Balint Kurti, P.J. 2023. Hybrid spatial-temporal Mueller matrix imaging spectropolarimeter for high throughput plant phenotyping. Applied Optics. 62:2078-2091. https://doi.org/10.1364/AO.483870.
DOI: https://doi.org/10.1364/AO.483870

Interpretive Summary: Spectral imaging uses multiple bands across the electromagnetic spectrum has been studied extensively in agriculture. While this technology allows us to use data from drones and other types of “remote sensing” systems to evaluate plant health, interpretation of the data is complicated by several factors. Primary among them is the so-called “bidirectional reflectance distribution function” (BRDF) effects, where the matte or glossy characteristics of a surface or leaf cause light to change its spectrum at different sun- and viewer-angles. Measurements of polarization of the light reflected from leaves is often used as an important part of the correction process to account for variation in BRDF. In this study we assessed methods of measuring light polarization with high spatial resolution with high throughput.

Technical Abstract: Many correlations exist between spectral reflectance or transmission with various phenotypic responses from plants. Of interest to us are metabolic characteristics, namely, how the various polarimetric components of plants may correlate to underlying environmental, metabolic, and genotypic differences among different varieties within a given species, as conducted during large field experimental trials. In this paper, we overview a portable Mueller matrix imaging spectropolarimeter, optimized for field use, by combining a temporal and spatial modulation scheme. Key aspects of the design include minimizing the measurement time while maximizing the signal-to-noise ratio by mitigating systematic error. This was achieved while maintaining an imaging capability across multiple measurement wavelengths, spanning the blue to near-infrared spectral region (405–730 nm). To this end, we present our optimization procedure, simulations, and calibration methods. Validation results, which were taken in redundant and non-redundant measurement configurations, indicated that the polarimeter provides average absolute errors of (5.3±2.2)×10^-3 and (7.1±3.1)×10^-3 , respectively. Finally, we provide preliminary field data (depolarization, retardance, and diattenuation) to establish baselines of barren and non-barren Zea maize hybrids (G90 variety), as captured from various leaf and canopy positions during our summer 2022 field experiments. Results indicate that subtle variations in retardance and diattenuation versus leaf canopy position may be present before they are clearly visible in the spectral transmission.