One Man's Shoes Help NASA Explain Water Clarity
Wearing white sneakers, a cowboy hat and overalls, Bernie Fowler walks into Maryland's Patuxent River every June to see how deep he can go and still see the tops of his shoes. As a young man he could see his feet on the river bottom as he stood chest-deep to net blue crabs. Now in his nineties, he ventures into the river to assess the water clarity. Fowler has been collecting this data point for the past 29 years and counting, calling it "sneaker depth."
Scientists make precise measurements of water clarity from satellite data, but the calculations can be complex and hard to explain to people outside the discipline of oceanography. Now NASA is adopting Fowler's sneaker idea to communicate satellite measurements of water clarity, enabling the observations to be shared easily with interested the general public, local governments or anyone who is interested. NASA scientists calling this algorithm "Fowler's Sneaker Depth" — the depth of water, in meters, at which a person can no longer see their white shoes. The study was published in the April 2017 edition of The Optical Society journal Optics Express.
Retired state senator Fowler has been using "sneaker depth" as a way to communicate local changes in water clarity to his neighbors and community. Water clarity is vital because sunlight must be able to reach deep beyond the surface to help underwater plants grow and maintain a healthy ecosystem. Throughout the world, coastal waters can become murky due to excess of suspended mineral particles (e.g. eroded soil) or abnormally high abundances of phytoplankton (microscopic algae). While these effects occur naturally, they can be exacerbated by human activity in a watershed, such as land clearing, urban development, and the release of under-treated sewage. Poor water clarity can drastically affect human health, the food chain, and the fishing industry.
This natural-color image shows the Patuxent River watershed and was acquired on April 13, 2016, by the Operational Land Imager (OLI) on the Landsat 8 satellite.
Image Credit: NASA's Earth Observatory images by Joshua Stevens, using Landsat data from the U.S. Geological Survey