A compact field-deployable optical instrument using fluorescence, absorbance, and scattering to identify and quantify contaminants and natural substances in water bodies is described. The instrument is capable of deployment on autonomous underwater and surface vehicles, manned vehicles, fixed platforms such as buoys, or access points in water supply or drainage networks. The instrument comprises (1) a flowcell, (2) multiple optical systems, (3) a data logger, (4) a power control board and computer, and (5) a battery. The instrument has been packaged in a cylindrical pressure case of 200 mm diameter and 300 mm length for electrically and mechanically seamless insertion as a STARFISH AUV payload module. The same module can be fitted with watertight end caps for use aboard other platforms, or simpler packaging can be employed for use in less demanding environments. For spectrofluorometry, the system uses six (expandable to twelve) electronically switchable excitation sources, allowing the construction of fluorescence excitation-emission matrices (EEMs). A deuterium-tungsten light source (185 to 1100 nm) is used in making UV-VIS absorbance measurements. Turbidity can be measured by nephelometry, using observations of light scattering at each excitation wavelength. The absorbance and turbidity capabilities provide useful water quality information and can also be used for correction of inner shielding effects. Validation of the instrument includes (1) comparison with a commercial luminescence spectrometer in measuring both standards and field samples, (2) comparisons of observed spectra with published optical characteristics for several chemicals, and (3) field demonstration aboard an AUV.

The characterization and field testing of a compact in situ optical instrument using fluorescence, absorbance, and scattering to identify and quantify contaminants and natural substances in water bodies are described. The instrument, based on a technology named LEDIF (LED-Induced Fluorescence) developed by Ng et al. (2012a) was configured for in situ long-term continuous monitoring at a fixed location. The optical performance and sensing capabilities of the instrument were assessed by calibrating against laboratory-prepared and commercial standards, and compared with several commercial sensors and published values. The effects on sensor response of temperature, pressure, and particle interference due to turbidity and total suspended solids were assessed and reported. Instrumental baseline shift over time, instrument detection limits, and the capability of LEDIF to determine characteristics such as quantum yield and intramolecular deactivation of fluorescence response, were also assessed. Experimental results match well with results from commercial instruments and published data. To demonstrate field deployment, the LEDIF instrument was installed at Chinese Garden of Singapore for longterm continuous monitoring of chlorophyll a (Chl a) and turbidity at a management-selected location. The analytes were chosen based on management's needs in recording temporal trends of algal biomass and water cloudiness to develop effective controls of inflow and outflow water quality. A monitoring record showing the temporal response of algal biomass to ambient conditions and turbidity variations is presented and discussed.

The LEDIF (LED-induced fluorescence) is an in situ optical instrument that utilizes fluorescence, absorbance, and scattering to identify and quantify substances in water bodies. In this study, matrix effects on fluorescence signals caused by inner filtering, temperature, intramolecular deactivation, turbidity, and pH were investigated, and compensation equations developed to correct measured values and improve accuracy. Multiple simultaneous matrix effect corrections were demonstrated with a laboratory sample subjected to known interferences and physical conditions. In general, compensation was found to be important to improve the accuracy of fluorescence measurements.

Air pollution exposure causes seven million deaths per year, according to the World Health Organization. Possessing knowledge of air quality and sources of air pollution is crucial for managing air pollution and providing early warning so that a swift counteractive response can be carried out. An optical prototype sensor (AtmOptic) capable of scattering and absorbance measurements has been developed to target in situ sensing of fine particulate matter (PM2.5) and volatile organic compounds (VOCs). For particulate matter testing, a test chamber was constructed and the emission of PM2.5 from incense burning inside the chamber was measured using the AtmOptic. The weight of PM2.5 particles was collected and measured with a filter to determine their concentration and the sensor signal-to-concentration correlation. The results of the AtmOptic were also compared and found to trend well with the Dylos DC 1100 Pro air quality monitor. The absorbance spectrum of VOCs emitted from various laboratory chemicals and household products as well as a two chemical mixtures were recorded. The quantification was demonstrated, using toluene as an example, by calibrating the AtmOptic with compressed gas standards containing VOCs at different concentrations. The results demonstrated the sensor capabilities in measuring PM2.5 and volatile organic compounds.

Assessing the aquatic chemistry of water bodies through sample collection is labor- and time-intensive with limits on discrete spatial coverage that may not provide a detailed representation of the system. A practical approach is to develop in situ sensors deployed aboard autonomous underwater vehicles (AUVs) for three-dimensional water chemistry mapping. For this purpose, a compact optical instrument (LEDIF) measuring fluorescence, absorbance, and scattering to quantify contaminants and natural substances in water bodies is packaged inside a pressure hull and attached to a highly modular and flexible AUV (Small Team of Autonomous Robotic FISH (STARFISH)). LEDIF-STARFISH was deployed at a reservoir in Singapore for in situ real-time chlorophyll a and turbidity data collection. Locations of potential algal hot spots were observed, providing unprecedented insight into the plankton biomass distribution of the reservoir at different times. The results showcase the instrument's potential in tracking spatiotemporal variability of substances in large water bodies.