Remote Sensing of Water Quality: HABs and TSS

A decline in water quality can have a devastating impact on surrounding communities, economies, and environments. Poor water quality affects the health of an ecosystem, especially if it causes a harmful algae bloom (HAB). HABs form when a colony of algae becomes too prolific and produces a toxic or harmful impact on the surrounding environment. These blooms can cause eutrophication and fish kills that are devastating to the fish and
plant populations in the area. They are often linked to increased pollution, total suspended solids (TSS), and nutrient-rich runoff. Therefore, it is critical to have a fast, comprehensive, and cost-effective approach to understanding water quality.

Monitoring and identifying water quality can be accomplished using UV-Vis-NIR spectroscopy. These studies are conducted in nearly every aquatic environment (freshwater or marine) to measure total suspended solids (TSS), biomass, dissolved organic matter, micro/macro algae speciation, as well as the mineralogy of suspended sediments. These metrics are useful in determining the origin and causation of HABS and other water quality concerns.

Detecting algae blooms is accomplished by identifying spectral features in the visible and NIR that are indicative of different chlorophylls and pigments in different species of algae. Hyperspectral and multi-spectral satellites are often used to measure water quality in large areas. Various algorithms are applied to satellite images to identify speciation and biomass and map them accordingly.

Striking satellite photos taken from space reveal how the earth’s toxic algae blooms dramatically increased as the climate warmed.

Aquatic radiometric readings are often of a significantly lower magnitude than a terrestrial measurement, emphasizing the benefit of a more sensitive sensor with a higher signal-to-noise ratio. Many spectral features ofminerals and sediments take place outside the visible to NIR, and so there are ambiguities between minerals for identification at the 350-1100nm range. It is beneficial to use a sensor with a higher spectral range and sensitivity, like the Naturaspec™, in studies targeting the minerology of suspended sediments.

Remote sensing reflectance is commonly used in studies to target water quality, Chl-a, sediments, CDOM, and other parameters. NASA has chosen the PSR-1100f for their in-situ measurements in their Delta-X campaign (Fichot et al., 2021). This campaign is aimed at using remote sensing technology to study water quality components in the Mississippi Delta. Using this data, Harringmeyer et al. (2024) have been able to successfully estimate water
quality components like TSS using calculated remote sensing reflectance (Rrs). Here are some figures from their research that demonstrate the ability to use Rrs for water quality monitoring.

Example graphs of estimation of Chl-a from Rrs and Inherent optical properties in water from NASAs applied remote sensing training program on HABs.

Remote sensing reflectance (Rrs) spectra measured during the field campaigns compared to TSS concentration. Rrs spectra colored by TSS from (A) Spring 2021 Delta-X Campaign.

Mass-specific (TSS-normalized) particulate absorption coefficient, ap*, spectra colored by Particulate Organic Carbon POC/TSS from (B) Fall 2021 Delta-X Campaign.

Spectral Evolution’s UV-Vis-NIR field-portable spectroradiometers are rugged and offer the best combination of high resolution and high sensitivity, resulting in the most precise spectral data from any field instrument available on the market. The wide variety of accessories and fore optics make our instruments the most
versatile spectroradiometers for all types of measurements, including reflectance, radiance, irradiance, and transmittance.