reflectivity and color of biological subjects
analysis of uv-vis reflectance and reflected color of biological subjects – birds, insects, fruits, vegetables and more – is
conveniently achieved with a modular sensing system. considerations such as instrument footprint, light source
requirements and power needs are resolved using a configured for field portability.
introduction:
various biological samples exhibit uv-vis reflectivity and color characteristics of interest to researchers. applications are
diverse: for example, among some species of birds, insects and reptiles, uv reflectance and color play a role in mating
behavior, recognizing species and assessing predator risk. color as an indicator of fruit and vegetable ripening is significant;
also, chlorophyll distribution in crops, measured using reflectance, can tell growers something about optimum fertilizer
amounts. many more similar applications, both in the field and in the lab, can be classified as bioreflectance applications.
provides a particularly compelling option for bioreflectance applications in the field, where portability, flexibility and ease
of use are critical. is a modular spectrometer-based system that integrates into a single stack those components that
otherwise would have to be handled separately: the spectrometer, microprocessor with low-power display (in place of a pc),
light source, battery pack and even ethernet capability for remote measurements. reflection probes and other sampling
optics connect easily to the , keeping the overall system footprint compact and manageable.
experimental conditions
a typical configuration for portable uv-vis reflectance comprises the spectrometer set from 200-850 nm, with a 25 µm
slit and l2 detector collection lens. also installed in the stack is the -b battery module, which has two slots for sd card
data storage, and the -px, a high-intensity pulsed xenon light source with up to four hours battery life on a single charge. spectrasuite spectrometer operating software is also recommended. depending on experiment considerations, other options
to consider are the -e ethernet module and the spectrasuite-par add-on software application, which is used to
calculate photosynthetically active radiation (par) values of horticultural samples.
most bioreflectance applications involve diffuse reflection of solid surfaces. our fiber optic reflection/backscattering
probescan measure diffuse or specular reflectance from a surface; a good choice for most uv-vis bioreflectance
applications isour qr600-7-sr/125f, a premium-grade probe with 600 µm core diameter in a six-around-one fiber
configuration. also, theprobe is solarization-resistant and has a 1/8” ferrule.
results
bioreflectance setups using miniature portable spectroscopy have become so simple to perform that even high school
science students have little problem with such setups. in one example, a student measured the reflection at 90º of
philodendron plant leaves, theorizing that reflectance values could be correlated to fertilizer levels. the results suggested
that plant reflectance at wavelengths >700 nm was insensitive to the stress of over-fertilization (at 4x the recommended
amount of fertilizer), while the peak within the 530-630 nm range was noticeably sensitive (i.e., had greater reflectivity) to
stress. the increased reflectivity related to a decrease in chlorophyll and to the effects of osmosis. water collected between
the leaf cell membrane and cell wall and exposed more of the leaf surface, which increased reflectivity.
conclusions
the inherent flexibility of the sensing system can be exploited for a number of uv-vis bioreflectance applications simply
by mixing and matching modules and selecting sampling optics most appropriate for your application. a high-intensity, low-power pulsed xenon source and solutions to system power requirements make an extremely reliable choice for field
and other measurements.
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