The Hyperspectral Advantage in Water Quality

In the expansive waters of Utah Lake near Provo, Utah, the proliferation of harmful algal blooms (HABs) increasingly threatens the balance of aquatic health. HABs are rapid algae growths in water bodies that produce toxins harmful to humans, wildlife, and the environment. These blooms can deplete oxygen in the water, block sunlight, and disrupt aquatic ecosystems, leading to the contamination and eventual death of marine life. Over recent years, HABs have become more frequent and severe, posing significant risks to the lake's ecosystem and surrounding communities dependent on this natural resource.

Utah Lake's eutrophic conditions, characterised by high nutrient levels, create an ideal environment for the rapid growth of harmful algae. Nutrient pollution from agricultural runoff, wastewater discharge, and stormwater primarily drives the lake's HABs. This pollution results in the excessive growth of toxin-producing cyanobacteria, contaminating the water, posing health risks to humans and wildlife, and disrupting recreational activities. As climate change intensifies, temperature and precipitation patterns alter, and conditions in Utah Lake become even more favourable for HABs. Warmer temperatures, combined with increased nutrient runoff from agricultural and urban areas, exacerbate the growth of harmful algae.

Between the early 2000s and now, numerous HAB events have been recorded, leading to water quality advisories and affecting recreational activities, wildlife, and local water supplies. Notable incidents include the extensive bloom in  2014 , which resulted in the death of a dog shortly after it drank water from the lake, and in  2016 , which resulted in the closure of the lake and surrounding areas, as well as significant health warnings. These events have turned Utah Lake into a focal point for scientific research, aiming to understand the complex interactions between nutrient runoff, climate, and algae proliferation.

This trend underscores the urgent need for effective monitoring and management strategies to mitigate the impacts of HABs on the lake's health and the well-being of the surrounding communities. Ongoing research seeks to develop effective mitigation strategies to manage and reduce the occurrence of HABs in the future.

Environmental monitoring agencies often prioritise protecting water resources and ensuring public health, but accurately assessing water quality poses significant challenges.

In response to the challenges in maintaining healthy water quality, end users have turned to advanced remote sensing monitoring techniques, including spaceborne HSI. This approach enables a comprehensive assessment of water bodies, tracking changes over time and developing targeted conservation and remediation strategies.

A primary goal of water quality monitoring is to ensure aquatic ecosystems' safety and health and maintain healthy drinking water supplies. Using HSI, water quality managers can identify contaminants, monitor eutrophication, and detect early warning signs of pollution, enabling prompt intervention and mitigation measures to protect water quality.

Traditional water quality monitoring methods, including MSI and in-situ sampling, often require higher spectral resolution and are dependent on ground infrastructure. However, HSI offers significant advantages. Its capability to capture hundreds of narrow bands enables precise detection of various water quality parameters, such as nutrient concentrations, sediment loads, and the presence of HABs.

Pixxel conducted this study on Utah Lake, a vital ecological and recreational resource in the U.S. State of Utah. Located in the heart of the Utah Valley, it is the largest freshwater lake in the state, covering approximately 148 square miles (383 sq km). Its vast expanse provides diverse habitats for numerous species of flora and fauna, making it a critical ecological asset in the region.

In addition to its environmental importance, Utah Lake serves as a cultural and recreational hub for local communities. Moreover, the lake plays a crucial role in supporting local economies and enhancing the quality of life for nearby residents. It attracts tourists and outdoor enthusiasts, generating revenue and job opportunities.

HSI has emerged as a powerful tool for detecting water quality issues, providing detailed information that surpasses traditional methods. By capturing a broad spectrum of light across numerous narrow bands, HSI allows for precise identification of various water quality parameters.

MSI and HSI are both used to analyse the spectral properties of objects, but they differ significantly in their capabilities:

• Multispectral Imaging (MSI) captures images in limited broad bands, typically around 3 to 10. These bands are often spaced widely apart, covering distant segments of the electromagnetic spectrum. MSI is beneficial for general classification and detection tasks but needs more detailed spectral information for more specific analyses.
• Hyperspectral Imaging (HSI), on the other hand, captures images in hundreds of narrow, contiguous bands across the electromagnetic spectrum. This high spectral resolution allows HSI to detect subtle differences in the spectral signatures of materials, making it particularly effective for identifying specific substances and their concentrations.

Hyperspectral remote sensing offers a higher spectral resolution compared to traditional multispectral imagery. While multispectral sensors capture data across a few distinct bands of the electromagnetic spectrum, hyperspectral sensors capture hundreds of very narrow and contiguous bands. The expanded spectral coverage allows for finer discrimination of spectral signatures associated with various water quality parameters.

The heightened spectral resolution of hyperspectral imagery enables the detection of subtle differences in the reflectance properties of different water constituents. Each substance in the water exhibits distinct spectral characteristics influenced by chemical composition and physical properties. By analysing a more extensive range of spectral bands, hyperspectral data enhances the accuracy and reliability of water quality assessments.

Specific bands in the electromagnetic spectrum are particularly informative for monitoring water quality parameters.

The importance of spectral resolution in HSI cannot be overstated, particularly in the context of water quality monitoring:

• Spatial resolution refers to the size of the smallest object that the sensor can detect. While spatial resolution is essential for mapping and visualising the distribution of water quality parameters across a body of water, it is often less critical than spectral resolution for the detailed analysis of water quality issues.
• Spectral resolution refers to the sensor's ability to distinguish between different wavelengths of light. High spectral resolution means that the sensor can detect minute differences in the spectral signatures of materials, which is crucial for identifying specific water quality parameters such as different types of pollutants or algal species.

In water quality monitoring, the ability to detect and differentiate between various contaminants and biological elements depends on spectral resolution. For example, distinguishing between different types of algae or detecting low concentrations of pollutants requires high spectral resolution. Conversely, while spatial resolution is essential for creating accurate water quality maps, the priority is often on identifying and quantifying specific substances, making spectral resolution the critical factor.

Having established the significance of spectral resolution in HSI for water quality monitoring, we now shift to specific insights for Utah Lake. We explore how nutrient runoff from urban and agricultural areas contributes to HABs. By examining these contributions, we better understand the sources of nutrient inputs on water quality.

Understanding the sources of nutrient runoff from urban and agricultural areas is crucial for addressing the health of Utah Lake. The preceding land cover maps illustrate how land use contributes to the nutrient load in the lake, which results in HABs. To further explore these nutrient inputs' impact, we focus on specific water quality indicators. The following maps of chlorophyll-a concentration, phytoplankton absorption, and phytoplankton carbon provide detailed insights into the lake's algal dynamics. These metrics, derived from Pixxel's HSI data, offer a detailed view of algal biomass activity, helping assess the severity and extent of HABs in Utah Lake.

Collectively, the HSI data presented in this study highlight the critical role of advanced remote sensing in monitoring and mitigating HABs. The nuanced data available from HSI, with its ability to capture detailed spectral information across a wide range of wavelengths, allows for precise detection and analysis of key water quality indicators.

Data products like the ones shown provide water quality managers with a comprehensive understanding of algae dynamics, enabling them to identify hotspots, track bloom development, and assess the effectiveness of intervention strategies in a timely manner. By leveraging HSI data, end users can develop targeted management practices and policy measures to reduce nutrient inputs, mitigate the impacts of HABs, and protect the health and sustainability of vital water resources like Utah Lake.

At Pixxel, we're transforming surface water quality assessments and safeguarding freshwater resources. With our upcoming constellation of high-resolution hyperspectral imaging satellites and analytical tools, we're building a comprehensive health monitor for our planet’s aquatic ecosystems. With pressing climate issues such as droughts and the contamination of freshwater sources, decision-makers and stakeholders must access hyperspectral imagery capabilities. With Pixxel's advanced solutions, they can gain unparalleled insights into water quality, enabling protective management strategies to protect and preserve surface water bodies.  Contact us  to learn how hyperspectral imaging satellites and their comprehensive datasets can benefit your water quality monitoring and management efforts. Alternatively,  download our whitepaper  to explore more applications in water management.

Pixxel is building a constellation of the world's highest-resolution hyperspectral Earth imaging satellites and the analytical tools to mine insights from their datasets.

Upon completion, this constellation will provide global coverage with a daily revisit rate to help detect, monitor, and predict global phenomena across agricultural, mining, environmental, and energy-generation use cases.

Hyperspectral imagery (HSI) presents itself as a valuable tool within environmental monitoring due to its capability to split the electromagnetic spectrum into many very narrow bands instead of the 5-15 bands captured by multispectral imaging (MSI) satellites. This wealth of information means that HSI can detect distinctive variations in spectral signatures of ground objects and scenes, capturing details that exceed beyond the visible spectrum and into the infrared range.

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