Satellite data has enabled researchers at the U.S. Geological Survey (USGS) to develop a new way to measure ocean depth. The technique, which uses imagery captured by the Landsat program, works specifically to determine ocean depth, or bathymetry, in shallow, nearshore environments.
Landsat, the longest-running satellite program dedicated to Earth observation, helps monitor environmental changes, urban growth, drought, wildfires, biomass changes and a host of other natural and man-made trends on a global scale.
A joint collaboration between NASA and the USGS, Landsat satellites have provided continuous Earth observation data since 1972. The latest satellite of the program—Landsat 9, developed by American multinational aerospace and defense company Northrop Grumman—launched in 2021.
A coastal bathymetry map shows the ocean’s depth off the Florida Keys. Researchers at the U.S. Geological Survey have developed a new method to measure ocean depth in shallow, near-shore environments.
A coastal bathymetry map shows the ocean’s depth off the Florida Keys. Researchers at the U.S. Geological Survey have developed a new method to measure ocean depth in shallow, near-shore environments.
NASA Earth Observatory/USGS
The newly developed bathymetry technique, described in a study published in the journal Remote Sensing, applies a sophisticated algorithm to Landsat data, namely, observations conducted by the Operational Land Imager and Operational Land Imager-2 sensors on the Landsat 8 and 9 satellites.
There is a significant need for refined shallow-water maps, but producing them is a challenging endeavor. Traditionally, bathymetric mapping has tended to involve ship-based sonar and aircraft-based LiDAR surveys—both of which are costly and labor-intensive.
But for decades researchers have also been trying to refine bathymetric mapping via satellites in an effort to fill in knowledge gaps in some coastal areas.
In the United States alone, coastal waters are only 52 percent mapped, according to Jeff Danielson, one of the authors of the latest study with the USGS.
“It’s one of the hot topics in geospatial sciences right now,” Danielson said in a NASA Earth Observatory press release. “There is a niche to fill in bathymetry gaps with a new tier of data.”
In Alaska, for example, bathymetry mapping is lacking for large swaths of the state’s coastal waters because harsh weather, seasonal sea ice and strong currents have made conventional efforts difficult.
Satellite bathymetry mapping can help to provide critical data for modeling waters movement, tracking coastal changes and studying coral reef habitats, among other applications.
The newly developed technique is based on measurements of sunlight penetrating the water and reflecting off the seafloor, which can provide an indication of water depth in sufficiently shallow seas. This is easier when the water is clear and the seafloor is bright, with the technique capable of mapping depths greater than 65 feet.
But the method becomes more challenging when the water is not as clear, thanks to factors such as sediment or plankton, or the seafloor is not bright—perhaps because it is covered by grass.
In an attempt to address this, the USGS researchers corrected for these kinds of factors when developing the algorithm, although their model becomes less accurate when unusual components are present—such as a bloom of a specific phytoplankton species or a rare kind of dark volcanic seafloor.
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Reference
Kim, M., Danielson, J., Storlazzi, C., & Park, S. (2024). Physics-Based Satellite-Derived Bathymetry (SDB) Using Landsat OLI Images. Remote Sensing, 16(5), 843. https://doi.org/10.3390/rs16050843