historic and recent Landsat water clarity assessments have been conducted on more
than 20,000 lakes to investigate spatial and temporal patterns and explore factors
that affect water quality. The spatial characteristics of Landsat imagery allow for
the assessment of all lakes larger than ~4 ha, but the broad nature and placement of
its spectral bands have limited assessments largely for water clarity. European
Space Agency (ESA) MERIS imagery with spectral bands that were selected for
water has been used to assess chlorophyll for about 900 of Minnesota’s large lakes
(those > 150 ha). Improvements of the recently launched Landsat 8 and upcoming
ESA Sentinel-2 satellites will expand our capabilities further enabling assessment
of other optically related water quality characteristics, such as chlorophyll, colored
dissolved organic matter (CDOM), and mineral suspended solids for all lakes, and
upcoming Sentinel-3 will continue these capabilities for large lakes.
Keywords CDOM • Chlorophyll a • Lake water quality • Satellite imagery
Landsat • Secchi depth • Sentinel
1 Introduction
Inland water bodies, such as lakes and reservoirs, are important natural resources
for sustenance, recreation, and aesthetic enjoyment, and they add to the economic
vitality and quality of life of regions where they occur. Water quality properties,
such as chlorophyll a, total suspended matter, turbidity, colored dissolved organic
matter (CDOM), and nutrients, are used by regulatory and resource management
agencies to guide management and public safety decisions. In situ point sampling is
the conventional method for collecting information on water quality variables. For
effective lake management, it is important to have long-term water quality information on a synoptic scale. The “big picture” view of water quality allows managers to take into account not only differences among lakes but also changes
through time for the whole lake and surrounding water bodies within a watershed
or typically much larger areas. Unfortunately, only a small percentage of inland
waters are regularly monitored by conventional methods, and historical water
quality data are lacking for most inland waters. The “big picture” view of water
quality is not practical with conventional point sampling methods due to limited
resources, and historic water quality data are sparse. Satellite remote sensing has
become a viable option for current synoptic measurements and historic assessments
of important water quality variables due to improved computer software and
hardware, as well as the availability of free or inexpensive satellite imagery.
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L.G. Olmanson et al.
than 20,000 lakes to investigate spatial and temporal patterns and explore factors
that affect water quality. The spatial characteristics of Landsat imagery allow for
the assessment of all lakes larger than ~4 ha, but the broad nature and placement of
its spectral bands have limited assessments largely for water clarity. European
Space Agency (ESA) MERIS imagery with spectral bands that were selected for
water has been used to assess chlorophyll for about 900 of Minnesota’s large lakes
(those > 150 ha). Improvements of the recently launched Landsat 8 and upcoming
ESA Sentinel-2 satellites will expand our capabilities further enabling assessment
of other optically related water quality characteristics, such as chlorophyll, colored
dissolved organic matter (CDOM), and mineral suspended solids for all lakes, and
upcoming Sentinel-3 will continue these capabilities for large lakes.
Keywords CDOM • Chlorophyll a • Lake water quality • Satellite imagery
Landsat • Secchi depth • Sentinel
1 Introduction
Inland water bodies, such as lakes and reservoirs, are important natural resources
for sustenance, recreation, and aesthetic enjoyment, and they add to the economic
vitality and quality of life of regions where they occur. Water quality properties,
such as chlorophyll a, total suspended matter, turbidity, colored dissolved organic
matter (CDOM), and nutrients, are used by regulatory and resource management
agencies to guide management and public safety decisions. In situ point sampling is
the conventional method for collecting information on water quality variables. For
effective lake management, it is important to have long-term water quality information on a synoptic scale. The “big picture” view of water quality allows managers to take into account not only differences among lakes but also changes
through time for the whole lake and surrounding water bodies within a watershed
or typically much larger areas. Unfortunately, only a small percentage of inland
waters are regularly monitored by conventional methods, and historical water
quality data are lacking for most inland waters. The “big picture” view of water
quality is not practical with conventional point sampling methods due to limited
resources, and historic water quality data are sparse. Satellite remote sensing has
become a viable option for current synoptic measurements and historic assessments
of important water quality variables due to improved computer software and
hardware, as well as the availability of free or inexpensive satellite imagery.
112
L.G. Olmanson et al.