Arthur I. Zygielbaum

Seasonal Variation in the NDVI–Species Richness Relationship in a Prairie Grassland Experiment (Cedar Creek)

Species richness generally promotes ecosystem productivity, although the shape of the relationship varies and remains the subject of debate. One reason for this uncertainty lies in the multitude of methodological approaches to sampling biodiversity and productivity, some of which can be subjective. Remote sensing offers new, objective ways of assessing productivity and biodiversity. In this study, we tested the species richness–productivity relationship using a common remote sensing index, the Normalized Difference Vegetation Index (NDVI), as a measure of productivity in experimental prairie grassland plots (Cedar Creek). Our study spanned a growing season (May to October, 2014) to evaluate dynamic changes in the NDVI–species richness relationship through time and in relation to environmental variables and phenology. We show that NDVI, which is strongly associated with vegetation percent cover and biomass, is related to biodiversity for this prairie site, but it is also strongly influenced by other factors, including canopy growth stage, short-term water stress and shifting flowering patterns. Remarkably, the NDVI-biodiversity correlation peaked at mid-season, a period of warm, dry conditions and anthesis, when NDVI reached a local minimum. These findings confirm a positive, but dynamic, productivity–diversity relationship and highlight the benefit of optical remote sensing as an objective and non-invasive tool for assessing diversity–productivity relationships.

Detection and measurement of vegetation photoprotection stress response using PAR reflectance

Optical reflectance from leaf surfaces has been known for decades to increase with decreasing leaf water content. Experimental results show this increase consistently in maize in the visible (photosynthetically active radiation—PAR) and middle infrared (MIR) spectral regions, and with weaker correlation in the near infrared (NIR) region. Changes in chlorophyll concentration have been shown to be too small to substantially contribute to increasing reflectance during the duration of these experiments. Therefore, the reflectance responses to water deficit are perplexing since reflectance in the PAR region is dominated by pigment absorption, while reflectance in the MIR region is dominated by water molecule absorption. We report on recent experiments with maize that indicate that the reflectance changes during water stress in the PAR and MIR regions are due to changing optical absorption, whilst those in the NIR region are due to changing optical scatter. In addition, reflectance in PAR and MIR appears to be ...

Proximal sensing to detect symptoms associated with wheat curl mite-vectored viruses

The wheat curl mite (WCM) is microscopic, and therefore mite movement is difficult to track in the field. However, the virus complex it transmits causes observable and measurable changes to chlorophyll content and biomass. The ability to detect WCM (vectored viruses) with remote sensing was investigated by comparing vegetation indices calculated from proximal sensing data to ground-reference data obtained in the field. Of the 10 vegetation indices evaluated, the red-edge position (REP) provided the best relationship with virus symptoms observed in wheat. There was a significant and high correlation between REP and relative chlorophyll values and biomass and a significant, but lower, correlation between REP and percentage virus infection.

Static Analysis and Dimensional Optimization of a Cable-Driven Parallel Robot

A cable-driven parallel manipulator has been chosen to suspend and navigate instruments over a phenotyping research facility at the University of Nebraska. This paper addresses the static analysis and dimensional optimization of this system. Analysis of the system was performed with catenary simplification to create force equilibrium equations and define a mathematical model. The model incorporates flexibility due to catenary sag of the cables. Cable axial stiffness was not included because stiffness is dominated by catenary flexibility for the expected cable tensions. The model was used to optimize system dimensions, and a twelfth-scale system was constructed to verify the model as well as enable dynamic and control system experimentation during full-scale system construction. Miniature end-effectors were used to obtain end-effector orientation and cable tension measurements which were comparable to model predictions. The mathematical model was thereby shown to be accurate for the purpose of system static analysis.

Stability improvement of a four cable-driven parallel manipulator using a center of mass balance system

A four cable-driven parallel manipulator (CDPM), consisting of sophisticated spectrometers and imagers, is under development for use in acquiring phenotypic and environmental data over an acre-sized crop field. To obtain accurate and high quality data from the instruments, the end effector must be stable during sensing. One of the factors that reduces stability is the center of mass offset of the end effector, which can cause a pendulum effect or undesired tilt angle. The purpose of this work is to develop a system and method for balancing the center of mass of a 12th-scale CDPM to minimize vibration that can cause error in the acquired data. A simple method for balancing the end effector is needed to enable end users of the CDPM to arbitrarily add and remove sensors and imagers from the end effector as their experiments may require. A Center of Mass Balancing System (CMBS) is developed in this study which consists of an adjustable system of weights and a gimbal for tilt mitigation. An electronic circuit board including an orientation sensor, wireless data communication, and load cells was designed to validate the CMBS. To measure improvements gained by the CMBS, several static and dynamic experiments are carried out. In the experiments, the dynamic vibrations due to the translational motion and static orientation were measured with and without CMBS use. The results show that the CMBS system improves the stability of the end-effector by decreasing vibration and static tilt angle.