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Artist's image of Landsat 8

Artist's image of Landsat 8 (Image by NASA/Goddard Space Flight Center Conceptual Image Lab)

Contact information
For information on Lakes in Wisconsin, contact:
Wisconsin DNR Lakes
Division of Water
Bureau of Water Quality
Citizen Lake Monitoring Contacts

Future directions

Future remote sensing research activities at the Wisconsin DNR will concentrate on an increase in Earth observation monitoring capabilities. These research activities include the optical and biogeochemical characterization of lakes across Wisconsin and the development of models for the retrieval of the concentrations of algal pigments, suspended solids, and colored dissolved organic matter (CDOM) for future satellite sensors.

Physical principles of the remote sensing of water quality

Models for the remote sensing of water quality depend on the relationship of the light reflected from a lake, called the remote sensing reflectance Rrs(λ), and the inherent optical properties of the constituents, comprised of the absorption coefficient a(λ) and the backscattering coefficient bb(λ). The remote sensing reflectance depends on the solar zenith angle, θ, solar azimuth angle, φ, and wavelength, λ, and the distinctive reflectance features of lakes are the result of variations in a(λ) and bb(λ). The inherent optical properties of the constituents provide information for the development of models for the retrieval of the concentrations of the constituents of interest from the remote sensing reflectance.

Calculation of remote sensing reflectance

Calculation of remote sensing reflectance


This graph is comprised of two panels. The panel to the left shows a picture of Trout Lake in Vilas County overlaid with two sets of white arrows to represent the ratio of downwelling irradiance, Ed(λ), to water leaving radiance, Lw(θ, φ, λ). The panel to the right translates this information to the formula for the calculation of remote sensing reflectance, Rrs(θ, φ, λ).

Remote sensing reflectance spectra of lakes

Remote sensing reflectance spectra represent the spectral signatures of lakes and are determined by the inherent optical properties of the constituents. The distinctive reflectance features of lakes in the blue spectral region are related to the presence of algal pigments, non-algal particles, and CDOM. The spectral features in the red spectral region are mainly related to the presence of algal pigments. The remote sensing reflectance spectrum for Trout Lake from 06/17/2014 is typical for many clear lakes in northern Wisconsin and shows a small reflectance trough at a wavelength of 672 nm related to the presence of chlorophyll-a. This spectral feature is used to differentiate chlorophyll-a from the rest of the constituents and to develop models for the retrieval of the concentration of chlorophyll-a from remote sensing data. The remote sensing reflectance spectrum for the Rainbow Flowage from the same day is typical for the stained flowages of the Wisconsin River. There are several reflectance peaks and troughs in the blue spectral region related to the presence of different algal pigments, non-algal particles, and CDOM. The increase in reflectance in the green spectral region seen in the spectrum for Trout Lake is suppressed by the presence of CDOM. The remote sensing reflectance spectrum for the Rainbow Flowage shows reflectance troughs at wavelengths of 624 and 666 nm related to the presence of phycocyanin and chlorophyll-a.

Remote sensing relectance spectra

Remote sensing reflectance spectra from 06/17/2013 for Trout Lake (left) and the Rainbow Flowage (right)


The graph consists of two line charts and compares two remote sensing reflectance spectra from 06/17/2013. The x-axis of each line chart has values from 400 to 750 nm and the y-axis has values from 0 to 0.005 sr-1. The spectra from Trout Lake (left) and the Rainbow Flowage (right) right have distinctive reflectance features typical for many lakes in Wisconsin and show the importance of specific spectral regions for the retrieval of water quality from remote sensing data.

Development of models for future satellite sensors

Data collection activities for the development of models for the retrieval of the concentrations of algal pigments, suspended solids, and CDOM for future satellite sensors include field measurements of remote sensing reflectance spectra for lakes across Wisconsin. These measurements are used to model the spectral bands of future satellite sensors capable of the differentiation of the constituents of interest and to calibrate and validate models for the retrieval of water quality data for these sensors.