The increasing prevalence of three-dimensional (3D) printing of optical housings and mounts necessitates a better understanding of the optical properties of printing materials. This paper describes a method for using multithickness samples of 3D printing materials to measure transmittance spectra at wavelengths from 400 to 2400 nm [visible to short-wave infrared (IR)]. In this method, 3D samples with material thicknesses of 1, 2, 3, and 4 mm were positioned in front of a uniform light source with a spectrometer probe on the opposing side to measure the light transmittance. Transmission depended primarily on the thickness and color of the sample, and multiple scattering prevented the use of a simple exponential model to relate transmittance, extinction, and thickness. A Solidworks file and a 3D printer file are included with the paper to enable measurements of additional materials with the same method.
Harmful and nuisance algal blooms are becoming a greater concern to public health, riparian ecosystems, and recreational uses of inland waterways. Algal bloom proliferation has increased in the Upper Clark Fork River in western Montana, USA, due to a combination of warming water temperatures, naturally high phosphorus levels, and an influx of contaminants through anthropogenic nitrogen enrichment along its banks. To improve understanding of bloom dynamics, such as algal biomass, a UAV-based hyperspectral imaging system was deployed to monitor several locations along the Upper Clark Fork River. Image data were collected across the spectral range of 400 - 1000 nm with 2.1 nm spectral resolution during two field sampling campaigns in 2021. Included are methods to estimate chlorophyll a standing crops using regression analysis of salient wavelength bands, before and after separating the pigments according to growth form. Estimates of total chlorophyll a standing crops generated through a brute-force analysis are compared to in-situ data, resulting in a maximum rsquared of 0.62 for estimating filamentous plus epiphytic chlorophyll a. Estimates of total and epilithic pigment standing crops are also included. The salient wavelengths bands used to estimate these pigments were then used as the basis for creating a low-cost imaging system for identifying algal blooms.
A low-cost multispectral imager is described for routine monitoring of Cladophora nuisance algae and bluegreen algae in narrow rivers that are not spatially resolved by satellites. The goal is to identify algal blooms and estimate the chlorophyll a (chl a) and phycocyanin content from a network of low-cost imagers that can be mounted on bridges, trees, or other convenient objects at key river locations. The preliminary design uses Raspberry Pi cameras and computers with bandpass filters at 568, 671, 700, and 825 nm, based on data gathered with an airborne hyperspectral imager on the Upper Clark Fork River in southwestern Montana USA. This paper summarizes the initial design, calibration measurements, and preliminary reflectance data.
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