Benchmarking a Portable Low-Cost Spectrometer for Algal Fluorescence: Applications in Remote Sensing and Water Quality Monitoring

Abstract. Philippine inland waters experience increasing pressures of nutrient enrichment and algal blooms which threaten water quality, biodiversity, and human health. Chlorophyll monitoring, the most critical indicator of algal biomass, plays a key role in eutrophication evaluation and identification of harmful algal blooms (HABs). Satellite and unmanned aerial vehicle (UAV)-based remote sensing technology provides large area chlorophyll-a mapping, with accuracy dependent on precise ground-truth measurements for calibration and validation. This paper presents the design and verification of a low-cost fluorescence spectrometer for potential in-situ chlorophyll-a measurement that supports geospatial benchmarking and the validation of remote sensing. The spectrometer consists of a Hamamatsu C12880MA mini spectrometer contained in a Raspberry Pi microcontroller with an LED-based excitation source to detect chlorophyll a fluorescence emission in Chlorella vulgaris samples. Laboratory tests compared the developed spectrometer with a commercial Ocean Optics fluorescence spectrometer, and with a high correlation between excitation spectra (R2 = 0.9304) and moderate correlation between emission spectra (R2 = 0.7269), validating that the system can detect chlorophyll-a fluorescence signals as relevant to the spectral bands used in satellite-based water quality indexes. Though proven under laboratory conditions, the low-cost, compact design provides for prospective field deployment for real-time monitoring. The built fluorescence spectrometer thus provides an emerging, scalable approach to ground-based spectral measurement, bridging laboratory instrumentation and geospatial remote sensing applications to improve the accuracy and temporal resolution of freshwater quality monitoring.