Metrics of surface water quality

Although satellite imagery cannot measure all aspects of the physical, chemical, and biological characteristics of lakes, it can efficiently measure several optically related constituents that are key indicators of water quality and ecological status: chlorophyll, phycocyanin (characteristic pigment of cyanobacteria), suspended solids, turbidity, colored dissolved organic matter (CDOM), and water clarity. Clarity, measured as Secchi depth (SD), is affected by all the previously listed indicators. These constituents absorb and/or scatter visible light at different wavelengths and thus affect the amount and spectral character of light reflected to satellite sensors. The reflected light measured
by sensors can be used to measure these constituents.

As the following link explains, the properties of light reflected from inland waters depend primarily on the relative abundance of three important “optical” constituents: plant pigments, CDOM, and turbidity (or suspended matter): Reflectance spectra related to dominant optical constituents. The links below provide background information and key findings from our measurements of water quality metrics by satellite imagery. Expand each term to see the different metrics of surface water quality at a glance, or click on their respective images to dive deeper.

Expand all

Lake Clarity

Water clarity, an indicator of water quality, is a loosely defined term generally related to how far one can see in a water body. Click on the image below to learn more.

Clear water with large rocks on shore.

Colored Dissolved Organic Matter (CDOM)

Colored (or chromophoric) dissolved organic matter (CDOM) is the part of organic matter that absorbs light in the blue and UV part of the electromagnetic spectrum, staining water a “tea-like” yellow-brown color. Click on the image below to learn more.

Bottled water with various levels of CDOM.

Chlorophyll a

Chlorophyll a is the primary pigment that captures light energy during photosynthesis. Click on the image below to learn more.

Chlorophyll under the microscope.

Turbidity and suspended matter

Turbidity is a measure of light scattering caused by suspended particles in natural waters. Click on the image below to learn more.

Mississippi River confluence.


Phycobilins are photosynthetic pigments unique to cyanobacteria (also referred to as blue green algae) and rhodophyta, or red algae. Click on the image below to learn more.

Sampling the surface.