Development of a Dual-beam Integrating Sphere Spectrophotometer for Measuring Absorption of Diffuse UV-VIS Radiation in Leaves and other Biological Samples

University Of Vermont & State Agricultural College, Burlington VT

Investigators

Abstract

This award is for the development of an integrating sphere spectrometer that will make it possible to measure the optical properties of leaves and other biological samples irradiated with diffuse and partially diffuse light. The instrument will be developed in the following stages: design of optics and electronics, assembly of the instrument, testing and validating the measurements against spectral standards and calculated values, creating a user interface, and making test and demonstration measurements of leaves and other biological samples. This integrating sphere spectrophotometer will make it possible to measure total reflectance (diffuse plus specular), transmittance, and absorptance in samples within the biologically important regions of the spectrum: ultraviolet-B (280-320 nm), ultraviolet-A (320-400 nm), photosynthetically active region (400-700 nm), and far-red near infra-red (700-1000 nm). The new instrument will significantly advance the measurement capability over current instrumentation, which allows for measurements only when samples are irradiated with direct light. The ability to quantify the radiation budget of samples irradiated with diffuse and partially diffuse light should have wide-ranging applications in a variety of disciplines where information about radiation interception and transport are fundamental, such as ecology, plant physiology, photobiology, photosynthesis, and studies of global climate change. The amount of sunlight that reaches the Earth's surface is one of the most important factors determining the productivity of crops, forests, and natural ecosystems. Sunlight is necessary for human and animal health as well, but it can also cause damage, as in the case of sunburn. In order to study the effects of light on plants and animals, it is necessary to accurately measure the amount of light that is absorbed by their tissues. This measurement is easy to make when light travels as a beam but is not possible to make when light is diffuse, as is the case on a cloudy day. Diffuse light represents a significant portion of the light environment on Earth, it enhances ecosystem productivity, and it is expected to increase with global climate change. The goal of this research is to develop new instrumentation that will make it possible to measure how much light is absorbed when plant or animal tissues are irradiated with diffuse light. The project will support the training of graduate and undergraduate students, high school teachers and students; and it presents an opportunity to recruit members of underrepresented groups to science.