NASA checks coastal waters from space
Using NASA satellite imagery, researchers at the University of South Florida (USF) in St. Petersburg have found that it is possible to monitor coastal water quality. This means that water quality can be checked daily rather than monthly as done by traditional methods which involves expensive boat surveys. This information can be crucial for resource managers devising restoration plans for coastal water ecosystems. According to the researchers, this method can be applied to coastal waters worldwide with little changes -- providing that resource managers have access to data from NASA satellites.
You can see above images showing that water quality of Florida's Tampa Bay decreases in winter months compared to summer. More particles suspended in the water, a measure called turbidity, show up as yellow, orange and red in December (left image) than in July (right). Images are composites of turbidity data collected in December and July, respectively, over a span of three years using NASA's MODIS instrument. (Credit: NASA/USF) Here is a link to a larger version of these pictures.
This research work has been done at the Institute for Marine Remote Sensing (IMaRS) at the University of South Florida in St. Petersburg. The project was led by Frank Müller-Karger, Professor and Director of the Institute, with the help of Chuanmin Hu, Assistant Research Professor and Executive Director, and of Zhiqiang Chen, a Post-doc Research Associate.
Here is how NASA describes the utility of this research work. "The team's findings will help tease out factors that drive changes in coastal water quality. For example, sediments entering the water as a result of coastal development or pollution can cause changes in water turbidity – a measure of the amount of particles suspended in the water. Sediments suspended from the bottom by strong winds or tides may also cause such changes. Knowing where the sediments come from is critical to managers because turbidity cuts off light to the bottom, thwarting the natural growth of plants. 'If we can track the source of turbidity, we can better understand why turbidity is changing. And if the source is human-related, we can try to manage that human activity,' says Frank Muller-Karger."
Observing turpidity was previously done with the help of boat surveys. NASA satellites are changing the process. "Satellites previously have observed turbidity in the open ocean by monitoring how much light is reflected and absorbed by the water. The technique has not had much success in observing turbidity along the coast, however. That’s because shallow coastal waters and Earth’s atmosphere serve up complicated optical properties that make it difficult for researchers to determine which colors in a satellite image are related to turbidity, which to shallow bottom waters, and which to the atmosphere. Now with advances in satellite sensors combined with developments in how the data are analyzed, Chen and colleagues show it is possible to monitor turbidity of coastal waters via satellite."
Now, let's see how the USF researchers have done to check the coastal waters of Tampa Bay. "To determine water clarity in Tampa Bay, the team looked at more than eight years of imagery from GeoEYE's Sea-viewing Wide Field-of-view Sensor (SeaWiFS) instrument, whose data is analyzed, processed and distributed by NASA for research. The images give a measure of how much light is reflected by the water. The data were put through a two-step calculation to arrive at a measure of clarity. Similarly, data from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard the Aqua satellite was compared with measurements of turbidity gathered on the ground and then applied to each whole image to make the maps."
This research work has been published in two separate papers in Remote Sensing of Environment.
- Monitoring turbidity in Tampa Bay using MODIS/Aqua 250-m imagery (Volume 109, Issue 2, Pages 207-220, July 30, 2007)
- Remote sensing of water clarity in Tampa Bay (Volume 109, Issue 2, Pages 249-259, July 30, 2007)
Sources: NASA's Goddard Space Flight Center news release, via EurekAlert!, August 29, 2007; and various websites
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